DNA replication, transcription, and translation are essential biological processes. DNA replication involves unwinding the DNA double helix and using each strand as a template to synthesize new strands through the actions of enzymes like DNA polymerase and ligase. Transcription copies the information in DNA to messenger RNA (mRNA) in the cell nucleus. Translation then uses the mRNA template to assemble a protein from amino acids on ribosomes based on the genetic code. These processes are precisely coordinated to allow genetic information to direct the synthesis of proteins.
DNA replication in eukaryotes occurs semi-conservatively, with each parental DNA strand serving as a template to create new daughter strands. It begins at origins of replication and proceeds bidirectionally. Enzymes such as helicase unwind the DNA double helix, while DNA polymerase adds complementary nucleotides to the leading and lagging strands. The lagging strand is synthesized discontinuously in short segments called Okazaki fragments. Telomeres protect chromosome ends from degradation during replication, and the telomerase enzyme maintains telomere length.
The nucleus is a membrane-bound organelle that houses the genetic material in eukaryotic cells. It was discovered in 1831 and named by Robert Brown. The nucleus stores DNA and RNA, enables protein synthesis, and houses the nucleolus where ribosomes are produced. It occupies about 10% of the cell volume and is surrounded by a double membrane with nuclear pores that regulate transport. The nuclear lamina provides structure and chromatin contains the genome. Within the nucleus, the nucleolus is the site of ribosome biogenesis through rRNA transcription and processing.
Tommy was born small and had frequent illnesses as a child. He remained short as an adult and was diagnosed with intestinal cancer at age 22. Additional unrelated tumors appeared over the next 10 years. Testing revealed Tommy had Bloom syndrome, a rare genetic disorder characterized by short stature, facial rashes from sun exposure, small head size, and high risk of multiple cancers. Bloom syndrome results from a defective gene that encodes a DNA helicase enzyme, causing errors in DNA replication and increased mutations.
A nonsense mutation is a point mutation that introduces a premature stop codon into the coding region of a gene. This results in only a partial protein being produced, as the stop codon signals the ribosome to terminate translation early. These truncated proteins are often nonfunctional or defective.
The lac operon regulates genes involved in lactose metabolism in E. coli. It is negatively regulated by the lac repressor protein, which binds to the operator region and blocks transcription when lactose is absent. However, in the presence of lactose or another inducer molecule, the repressor dissociates from the DNA, allowing transcription and expression of the genes required to break down and utilize lactose.
Gene regulation in prokary
DNA is composed of nucleotides that contain nitrogen bases, sugars, and phosphates. The order of these nucleotides determines the genetic code. DNA exists as a double helix structure with two complementary strands joined by hydrogen bonds between nitrogen bases on each strand. This double helix structure allows DNA to efficiently store and replicate genetic information.
DNA replication is a complex process that involves unwinding of the DNA double helix, synthesis of new strands that are complementary to the original strands, and enzymes such as DNA polymerase and helicase. There are multiple origins of replication in eukaryotes that allow bidirectional replication from many starting points along DNA molecules. Enzymes involved include DNA polymerase alpha that works with primase to initiate DNA synthesis, and DNA polymerases delta and epsilon that carry out leading and lagging strand elongation. Telomeres prevent shortening of chromosomes with each round of replication through the action of telomerase.
Nucleic acids are biopolymers composed of nucleotides as repeating units. DNA contains the genetic instructions for living organisms, while RNA assists in decoding this information. A nucleotide contains a phosphate group, a sugar (ribose in RNA and deoxyribose in DNA), and a nitrogenous base. DNA exists as a double helix with base pairing between adenine-thymine and guanine-cytosine. It undergoes replication to make copies for cell division. During transcription, RNA is synthesized from a DNA template, and translation follows to produce proteins from mRNA instructions. Mutation, control of gene expression, and the central dogma of molecular biology maintain and regulate the flow of genetic information.
This power point presentation explains double helical structure of DNA as proposed by Watson and Crick (1953).Attempts have also been made to high light the valuable contributions made by Rosalind Franklin and Wilkins. Brief details of different types of DNA have also been included.
DNA replication in eukaryotes occurs semi-conservatively, with each parental DNA strand serving as a template to create new daughter strands. It begins at origins of replication and proceeds bidirectionally. Enzymes such as helicase unwind the DNA double helix, while DNA polymerase adds complementary nucleotides to the leading and lagging strands. The lagging strand is synthesized discontinuously in short segments called Okazaki fragments. Telomeres protect chromosome ends from degradation during replication, and the telomerase enzyme maintains telomere length.
The nucleus is a membrane-bound organelle that houses the genetic material in eukaryotic cells. It was discovered in 1831 and named by Robert Brown. The nucleus stores DNA and RNA, enables protein synthesis, and houses the nucleolus where ribosomes are produced. It occupies about 10% of the cell volume and is surrounded by a double membrane with nuclear pores that regulate transport. The nuclear lamina provides structure and chromatin contains the genome. Within the nucleus, the nucleolus is the site of ribosome biogenesis through rRNA transcription and processing.
Tommy was born small and had frequent illnesses as a child. He remained short as an adult and was diagnosed with intestinal cancer at age 22. Additional unrelated tumors appeared over the next 10 years. Testing revealed Tommy had Bloom syndrome, a rare genetic disorder characterized by short stature, facial rashes from sun exposure, small head size, and high risk of multiple cancers. Bloom syndrome results from a defective gene that encodes a DNA helicase enzyme, causing errors in DNA replication and increased mutations.
A nonsense mutation is a point mutation that introduces a premature stop codon into the coding region of a gene. This results in only a partial protein being produced, as the stop codon signals the ribosome to terminate translation early. These truncated proteins are often nonfunctional or defective.
The lac operon regulates genes involved in lactose metabolism in E. coli. It is negatively regulated by the lac repressor protein, which binds to the operator region and blocks transcription when lactose is absent. However, in the presence of lactose or another inducer molecule, the repressor dissociates from the DNA, allowing transcription and expression of the genes required to break down and utilize lactose.
Gene regulation in prokary
DNA is composed of nucleotides that contain nitrogen bases, sugars, and phosphates. The order of these nucleotides determines the genetic code. DNA exists as a double helix structure with two complementary strands joined by hydrogen bonds between nitrogen bases on each strand. This double helix structure allows DNA to efficiently store and replicate genetic information.
DNA replication is a complex process that involves unwinding of the DNA double helix, synthesis of new strands that are complementary to the original strands, and enzymes such as DNA polymerase and helicase. There are multiple origins of replication in eukaryotes that allow bidirectional replication from many starting points along DNA molecules. Enzymes involved include DNA polymerase alpha that works with primase to initiate DNA synthesis, and DNA polymerases delta and epsilon that carry out leading and lagging strand elongation. Telomeres prevent shortening of chromosomes with each round of replication through the action of telomerase.
Nucleic acids are biopolymers composed of nucleotides as repeating units. DNA contains the genetic instructions for living organisms, while RNA assists in decoding this information. A nucleotide contains a phosphate group, a sugar (ribose in RNA and deoxyribose in DNA), and a nitrogenous base. DNA exists as a double helix with base pairing between adenine-thymine and guanine-cytosine. It undergoes replication to make copies for cell division. During transcription, RNA is synthesized from a DNA template, and translation follows to produce proteins from mRNA instructions. Mutation, control of gene expression, and the central dogma of molecular biology maintain and regulate the flow of genetic information.
This power point presentation explains double helical structure of DNA as proposed by Watson and Crick (1953).Attempts have also been made to high light the valuable contributions made by Rosalind Franklin and Wilkins. Brief details of different types of DNA have also been included.
1. DNA replication is the process where parental DNA is used as a template to produce identical copies of DNA or daughter DNA. It ensures faithful transmission of genetic material to offspring.
2. Replication starts at specific origins of replication and involves initiation, elongation, and termination phases. Enzymes involved include DNA polymerases, helicases, primases, ligases and more.
3. Eukaryotic replication is more complex, with multiple polymerases and regulated initiation. Telomerase is required for end-replication and chromosome integrity.
4. DNA repair mechanisms include base excision, nucleotide excision, mismatch and double-strand break repair to fix errors and damage via pathways like non-homologous
DNA supercoiling occurs when the DNA double helix is over- or under-wound, known as positive and negative supercoiling respectively. The degree of supercoiling is numerically expressed using the linking number which accounts for twists and writhes in the DNA helix. Topoisomerases are enzymes that relieve torsional strain in supercoiled DNA by introducing nicks in one or both strands, allowing the strands to pass through one another and change the linking number.
The document summarizes key aspects of the cell cycle and cell division. It discusses the phases of the cell cycle including interphase and mitosis. It describes chromosome structure and duplication. It explains the process of mitosis and cytokinesis. It also discusses regulation of the cell cycle through checkpoints at the G1/S and G2/M transitions to ensure DNA integrity before cell division.
DNA repair mechanisms are essential for maintaining genomic integrity. There are several pathways for repairing different types of DNA damage: mismatch repair fixes errors during DNA replication, base excision repair removes damaged bases, nucleotide excision repair replaces larger sections of damaged DNA, and double-strand break repair fixes breaks in both DNA strands. Defects in DNA repair genes can lead to increased cancer risks and genetic disorders like xeroderma pigmentosum and Fanconi anemia. Overall, DNA repair helps prevent mutations from being passed to new cells.
DNA is maintained in a compressed, supercoiled state.
But basis of replication is the formation of strands based on specific bases pairing with their complementary bases
This document discusses exon shuffling, which is a mechanism by which new genes can form through the rearrangement of exons from different genes. Exon shuffling was first proposed in 1978 and involves recombination within introns that allows exons to be assorted independently, generating new exon combinations. There are three main types of exon shuffling: exon duplication, insertion, and deletion. Exon shuffling generates genetic variation and mosaic proteins, and it has played a major role in evolution. The mechanisms involved are crossover during sexual recombination and transposon-mediated movements that can cut, paste, or copy and paste exons into new locations.
DNA replication is the process where a cell makes an identical copy of its DNA before cell division. It occurs in S phase of the cell cycle. DNA polymerase enzymes add nucleotides to each DNA strand based on complementary base pairing. This results in two identical DNA double helices, each with one original strand and one newly synthesized strand. In eukaryotes, DNA replication is more complex, involving multiple origins of replication and DNA polymerases. Mechanisms like proofreading and DNA repair help ensure high-fidelity copying of the genome.
DNA replication is the process by which a cell makes an identical copy of its DNA. There are three proposed models of replication: conservative, semi-conservative, and dispersive. Meselson-Stahl experiments provided evidence supporting the semi-conservative model. DNA replication involves unwinding of the DNA double helix, synthesis of an RNA primer, and elongation of the DNA strands by DNA polymerase. Telomeres protect chromosome ends from degradation during replication. Cancer cells maintain telomere length through expression of telomerase. Maintaining healthy lifestyle habits can help lengthen telomeres and delay aging.
DNA repair systems are essential for maintaining the integrity of genetic information. There are multiple pathways for repairing different types of DNA damage:
1) Mismatch repair corrects errors made during DNA replication by using methylation patterns to distinguish the template strand.
2) Base-excision repair involves DNA glycosylases that remove damaged bases, leaving abasic sites that are then repaired.
3) Nucleotide-excision repair removes larger distortions in the DNA double helix.
4) Direct repair mechanisms like photoreactivation can directly reverse some types of damage using light or chemical processes, without removing nucleotides. DNA repair pathways help prevent mutations and ensure fidelity of genetic information.
This document provides an outline and summary of a presentation on DNA replication in prokaryotes. The presentation was assigned by Mam Fatima and involved several participants who discussed:
1) DNA replication in prokaryotes begins at the origin of replication site (oriC) where DnaA protein binds and unwinds the DNA. Bidirectional replication forks are formed.
2) Enzymes such as helicase, primase, DNA polymerase III and ligase are involved in semi-conservative DNA replication. The leading strand replicates continuously while the lagging strand replicates discontinuously in Okazaki fragments.
3) Elongation occurs as DNA polymerases add nucleotides to the growing DNA strands in
The genetic material must produce a large number of copies of itself during the life cycle of an organism. The process by which a DNA molecule makes its identical copies is called DNA replication. The DNA molecule that undergoes replication may be termed as ‘parent molecule or template molecule, while the two molecules produced by replication may be called progeny molecules or daughter molecules.
The central dogma describes the flow of genetic information from DNA to RNA to protein. DNA is first replicated to produce two identical DNA molecules. Transcription then produces mRNA from DNA, which differs in that only one DNA strand is used as a template. Translation follows, using the mRNA to direct protein synthesis on ribosomes with the help of tRNA. Mutations can occur in genes and chromosomes, altering DNA sequences and potentially changing protein functions or structures. Common gene mutations include substitutions, insertions, deletions, duplications, and frameshifts, while chromosome mutations involve translocations, deletions, duplications, inversions, and isochromosomes.
The document discusses DNA replication and transcription. It describes the structure of DNA and RNA, how DNA replicates semiconservatively, and how transcription occurs. DNA replication takes place during the S phase of the cell cycle in the nucleus. It involves unwinding of the DNA double helix, synthesis of new leading and lagging strands of DNA in the 5' to 3' direction, and joining of Okazaki fragments. Transcription involves unwinding of the DNA helix, RNA polymerase binding to the promoter and synthesizing RNA complementary to one DNA strand in three phases - initiation, elongation, and termination.
DNA replication is the process by which DNA copies itself for transmission to daughter cells. In the late 1950s, three models were proposed for how DNA replicates: conservative, semi-conservative, and dispersive. Experiments showed that the semi-conservative model is correct, where each parental DNA strand acts as a template to replicate a new partner strand. DNA replication requires DNA and RNA polymerases, helicase, topoisomerases, primase, ligase and other proteins. It occurs through initiation, elongation and termination steps in both prokaryotes and eukaryotes, though eukaryotes have multiple replication origins and use RNA primers on the lagging strand.
The document provides information on the structure of DNA and RNA. It discusses how DNA was discovered to have a double helix structure by Watson and Crick in 1953 based on prior work by scientists like Franklin, Wilkins, Chargaff and Pauling. It describes the key components of DNA including the sugar-phosphate backbone, nitrogenous bases, and how the bases pair up in the double helix structure. It also discusses different DNA structures like A, B and Z-DNA and how DNA packages into nucleosomes and chromosomes. For RNA, it notes that it is similar to DNA but contains the sugar ribose and base uracil instead of thymine.
DNA repair mechanisms identify and correct damage to DNA that occurs due to normal cellular processes and environmental factors. There are two main types of DNA damage: endogenous damage caused by normal cellular processes and exogenous damage caused by external agents like UV radiation and chemicals. The main repair mechanisms are base excision repair, nucleotide excision repair, direct repair via photolyases, and error-prone repair systems like SOS repair. Together, these pathways maintain genome integrity by repairing different types of DNA lesions.
DNA can be damaged by physical, chemical, and environmental agents through various types of alterations including single or double base changes, breaks in the DNA chain, or cross-linkages between bases. The cell has multiple DNA repair mechanisms to correct damage including base excision repair, nucleotide excision repair, mismatch repair, and double-strand break repair. Base excision repair removes single damaged bases while nucleotide excision repair removes larger segments of damaged DNA. Mismatch repair corrects errors that occur during DNA replication. Double-strand break repair repairs more severe breaks in both strands of the DNA that can lead to chromosomal abnormalities. Defects in DNA repair pathways can result in increased cancer risks.
DNA replication is the process by which DNA copies itself. It involves unwinding the double helix and using each strand as a template to synthesize new complementary strands. Key enzymes involved include helicase, primase, DNA polymerase III, and ligase. DNA polymerase III is responsible for adding nucleotides to the new strands, while helicase unwinds the DNA and primase adds RNA primers. The process is semi-conservative, producing two DNA molecules each with one original and one new strand. Replication occurs through initiation, elongation, and termination stages and proofreading ensures high-fidelity copying of the genetic material.
DNA replication occurs through a semi-conservative process in both prokaryotes and eukaryotes. In prokaryotes, replication is bidirectional from a single origin and the replication forks meet, while in eukaryotes there are multiple origins of replication activated sequentially. Key enzymes involved include DNA polymerase, helicase, primase and ligase. Replication ensures the accurate transfer of genetic information between generations.
DNA replication is the process whereby a cell makes an identical copy of its DNA during cell division. It involves unwinding the DNA double helix into single strands, which then serve as templates for new strands to be synthesized in the opposite direction by DNA polymerases. The DNA polymerases can only add nucleotides to the 3' end of the growing strand, so replication occurs in both the 5' to 3' direction on one strand (the leading strand) and in short fragments joined together on the other (the lagging strand). Telomeres protect chromosome ends from erosion during replication. A complex team of enzymes including DNA polymerases, helicase, primase, ligase and single-stranded binding proteins work together to efficiently and
Watson and Crick discovered the double helix structure of DNA in 1953, suggesting a copying mechanism for genetic material. DNA replication involves unwinding the DNA helix, building new strands using existing strands as templates, and ensuring accurate copying. Several enzymes work together at the replication fork to copy DNA semi-conservatively. DNA polymerase adds nucleotides to growing strands using energy from nucleoside triphosphates. Okazaki fragments are produced on the lagging strand and joined by ligase. Telomeres prevent chromosome erosion after each replication. Together, this complex process copies the genome with high fidelity in a matter of hours.
1. DNA replication is the process where parental DNA is used as a template to produce identical copies of DNA or daughter DNA. It ensures faithful transmission of genetic material to offspring.
2. Replication starts at specific origins of replication and involves initiation, elongation, and termination phases. Enzymes involved include DNA polymerases, helicases, primases, ligases and more.
3. Eukaryotic replication is more complex, with multiple polymerases and regulated initiation. Telomerase is required for end-replication and chromosome integrity.
4. DNA repair mechanisms include base excision, nucleotide excision, mismatch and double-strand break repair to fix errors and damage via pathways like non-homologous
DNA supercoiling occurs when the DNA double helix is over- or under-wound, known as positive and negative supercoiling respectively. The degree of supercoiling is numerically expressed using the linking number which accounts for twists and writhes in the DNA helix. Topoisomerases are enzymes that relieve torsional strain in supercoiled DNA by introducing nicks in one or both strands, allowing the strands to pass through one another and change the linking number.
The document summarizes key aspects of the cell cycle and cell division. It discusses the phases of the cell cycle including interphase and mitosis. It describes chromosome structure and duplication. It explains the process of mitosis and cytokinesis. It also discusses regulation of the cell cycle through checkpoints at the G1/S and G2/M transitions to ensure DNA integrity before cell division.
DNA repair mechanisms are essential for maintaining genomic integrity. There are several pathways for repairing different types of DNA damage: mismatch repair fixes errors during DNA replication, base excision repair removes damaged bases, nucleotide excision repair replaces larger sections of damaged DNA, and double-strand break repair fixes breaks in both DNA strands. Defects in DNA repair genes can lead to increased cancer risks and genetic disorders like xeroderma pigmentosum and Fanconi anemia. Overall, DNA repair helps prevent mutations from being passed to new cells.
DNA is maintained in a compressed, supercoiled state.
But basis of replication is the formation of strands based on specific bases pairing with their complementary bases
This document discusses exon shuffling, which is a mechanism by which new genes can form through the rearrangement of exons from different genes. Exon shuffling was first proposed in 1978 and involves recombination within introns that allows exons to be assorted independently, generating new exon combinations. There are three main types of exon shuffling: exon duplication, insertion, and deletion. Exon shuffling generates genetic variation and mosaic proteins, and it has played a major role in evolution. The mechanisms involved are crossover during sexual recombination and transposon-mediated movements that can cut, paste, or copy and paste exons into new locations.
DNA replication is the process where a cell makes an identical copy of its DNA before cell division. It occurs in S phase of the cell cycle. DNA polymerase enzymes add nucleotides to each DNA strand based on complementary base pairing. This results in two identical DNA double helices, each with one original strand and one newly synthesized strand. In eukaryotes, DNA replication is more complex, involving multiple origins of replication and DNA polymerases. Mechanisms like proofreading and DNA repair help ensure high-fidelity copying of the genome.
DNA replication is the process by which a cell makes an identical copy of its DNA. There are three proposed models of replication: conservative, semi-conservative, and dispersive. Meselson-Stahl experiments provided evidence supporting the semi-conservative model. DNA replication involves unwinding of the DNA double helix, synthesis of an RNA primer, and elongation of the DNA strands by DNA polymerase. Telomeres protect chromosome ends from degradation during replication. Cancer cells maintain telomere length through expression of telomerase. Maintaining healthy lifestyle habits can help lengthen telomeres and delay aging.
DNA repair systems are essential for maintaining the integrity of genetic information. There are multiple pathways for repairing different types of DNA damage:
1) Mismatch repair corrects errors made during DNA replication by using methylation patterns to distinguish the template strand.
2) Base-excision repair involves DNA glycosylases that remove damaged bases, leaving abasic sites that are then repaired.
3) Nucleotide-excision repair removes larger distortions in the DNA double helix.
4) Direct repair mechanisms like photoreactivation can directly reverse some types of damage using light or chemical processes, without removing nucleotides. DNA repair pathways help prevent mutations and ensure fidelity of genetic information.
This document provides an outline and summary of a presentation on DNA replication in prokaryotes. The presentation was assigned by Mam Fatima and involved several participants who discussed:
1) DNA replication in prokaryotes begins at the origin of replication site (oriC) where DnaA protein binds and unwinds the DNA. Bidirectional replication forks are formed.
2) Enzymes such as helicase, primase, DNA polymerase III and ligase are involved in semi-conservative DNA replication. The leading strand replicates continuously while the lagging strand replicates discontinuously in Okazaki fragments.
3) Elongation occurs as DNA polymerases add nucleotides to the growing DNA strands in
The genetic material must produce a large number of copies of itself during the life cycle of an organism. The process by which a DNA molecule makes its identical copies is called DNA replication. The DNA molecule that undergoes replication may be termed as ‘parent molecule or template molecule, while the two molecules produced by replication may be called progeny molecules or daughter molecules.
The central dogma describes the flow of genetic information from DNA to RNA to protein. DNA is first replicated to produce two identical DNA molecules. Transcription then produces mRNA from DNA, which differs in that only one DNA strand is used as a template. Translation follows, using the mRNA to direct protein synthesis on ribosomes with the help of tRNA. Mutations can occur in genes and chromosomes, altering DNA sequences and potentially changing protein functions or structures. Common gene mutations include substitutions, insertions, deletions, duplications, and frameshifts, while chromosome mutations involve translocations, deletions, duplications, inversions, and isochromosomes.
The document discusses DNA replication and transcription. It describes the structure of DNA and RNA, how DNA replicates semiconservatively, and how transcription occurs. DNA replication takes place during the S phase of the cell cycle in the nucleus. It involves unwinding of the DNA double helix, synthesis of new leading and lagging strands of DNA in the 5' to 3' direction, and joining of Okazaki fragments. Transcription involves unwinding of the DNA helix, RNA polymerase binding to the promoter and synthesizing RNA complementary to one DNA strand in three phases - initiation, elongation, and termination.
DNA replication is the process by which DNA copies itself for transmission to daughter cells. In the late 1950s, three models were proposed for how DNA replicates: conservative, semi-conservative, and dispersive. Experiments showed that the semi-conservative model is correct, where each parental DNA strand acts as a template to replicate a new partner strand. DNA replication requires DNA and RNA polymerases, helicase, topoisomerases, primase, ligase and other proteins. It occurs through initiation, elongation and termination steps in both prokaryotes and eukaryotes, though eukaryotes have multiple replication origins and use RNA primers on the lagging strand.
The document provides information on the structure of DNA and RNA. It discusses how DNA was discovered to have a double helix structure by Watson and Crick in 1953 based on prior work by scientists like Franklin, Wilkins, Chargaff and Pauling. It describes the key components of DNA including the sugar-phosphate backbone, nitrogenous bases, and how the bases pair up in the double helix structure. It also discusses different DNA structures like A, B and Z-DNA and how DNA packages into nucleosomes and chromosomes. For RNA, it notes that it is similar to DNA but contains the sugar ribose and base uracil instead of thymine.
DNA repair mechanisms identify and correct damage to DNA that occurs due to normal cellular processes and environmental factors. There are two main types of DNA damage: endogenous damage caused by normal cellular processes and exogenous damage caused by external agents like UV radiation and chemicals. The main repair mechanisms are base excision repair, nucleotide excision repair, direct repair via photolyases, and error-prone repair systems like SOS repair. Together, these pathways maintain genome integrity by repairing different types of DNA lesions.
DNA can be damaged by physical, chemical, and environmental agents through various types of alterations including single or double base changes, breaks in the DNA chain, or cross-linkages between bases. The cell has multiple DNA repair mechanisms to correct damage including base excision repair, nucleotide excision repair, mismatch repair, and double-strand break repair. Base excision repair removes single damaged bases while nucleotide excision repair removes larger segments of damaged DNA. Mismatch repair corrects errors that occur during DNA replication. Double-strand break repair repairs more severe breaks in both strands of the DNA that can lead to chromosomal abnormalities. Defects in DNA repair pathways can result in increased cancer risks.
DNA replication is the process by which DNA copies itself. It involves unwinding the double helix and using each strand as a template to synthesize new complementary strands. Key enzymes involved include helicase, primase, DNA polymerase III, and ligase. DNA polymerase III is responsible for adding nucleotides to the new strands, while helicase unwinds the DNA and primase adds RNA primers. The process is semi-conservative, producing two DNA molecules each with one original and one new strand. Replication occurs through initiation, elongation, and termination stages and proofreading ensures high-fidelity copying of the genetic material.
DNA replication occurs through a semi-conservative process in both prokaryotes and eukaryotes. In prokaryotes, replication is bidirectional from a single origin and the replication forks meet, while in eukaryotes there are multiple origins of replication activated sequentially. Key enzymes involved include DNA polymerase, helicase, primase and ligase. Replication ensures the accurate transfer of genetic information between generations.
DNA replication is the process whereby a cell makes an identical copy of its DNA during cell division. It involves unwinding the DNA double helix into single strands, which then serve as templates for new strands to be synthesized in the opposite direction by DNA polymerases. The DNA polymerases can only add nucleotides to the 3' end of the growing strand, so replication occurs in both the 5' to 3' direction on one strand (the leading strand) and in short fragments joined together on the other (the lagging strand). Telomeres protect chromosome ends from erosion during replication. A complex team of enzymes including DNA polymerases, helicase, primase, ligase and single-stranded binding proteins work together to efficiently and
Watson and Crick discovered the double helix structure of DNA in 1953, suggesting a copying mechanism for genetic material. DNA replication involves unwinding the DNA helix, building new strands using existing strands as templates, and ensuring accurate copying. Several enzymes work together at the replication fork to copy DNA semi-conservatively. DNA polymerase adds nucleotides to growing strands using energy from nucleoside triphosphates. Okazaki fragments are produced on the lagging strand and joined by ligase. Telomeres prevent chromosome erosion after each replication. Together, this complex process copies the genome with high fidelity in a matter of hours.
DNA replication in prokaryotes occurs through a semi-discontinuous process at the replication fork. It begins with initiation proteins binding to the origin of replication and unwinding the DNA into single strands. DNA helicase then loads and unwinds the DNA further as single-strand binding proteins coat the exposed DNA. DNA primase adds RNA primers at the replication fork for DNA polymerase to begin DNA synthesis in the 5' to 3' direction. This results in continuous synthesis of the leading strand but discontinuous synthesis of the lagging strand as primers are repeatedly added. DNA ligase then seals the resulting Okazaki fragments on the lagging strand, completing replication of the bacterial chromosome.
1) DNA replication is the process by which DNA copies itself during cell division. It involves unwinding the DNA double helix and using each strand as a template to build new partner strands.
2) Key enzymes involved in DNA replication include helicase, which unwinds the DNA; DNA polymerase, which builds the new strands; and ligase, which seals the DNA.
3) The two strands of DNA replicate in opposite directions from a replication fork. One strand replicates continuously while the other replicates in fragments that are later joined.
DNA replication and repair involve complex multi-step processes. DNA is copied through semiconservative replication during S phase. This requires unwinding of the DNA double helix by helicase, synthesis of new strands by DNA polymerase using the parental strands as templates, and ligation by ligase. DNA polymerase can only add nucleotides to the 3' end, so the leading strand is continuously synthesized while the lagging strand involves discontinuous Okazaki fragments. Telomerase protects chromosome ends from shortening during replication. DNA repair pathways such as base excision repair and nucleotide excision repair help correct errors and damage to maintain genome integrity.
- DNA replication involves DNA copying itself exactly through a semi-conservative process that begins at the origin of replication and proceeds bidirectionally.
- The key enzymes involved are DNA helicase, topoisomerases, primase, DNA polymerase, and DNA ligase. DNA polymerase synthesizes new strands in the 5' to 3' direction using existing strands as templates.
- In eukaryotes, replication of the lagging strand occurs through discontinuous Okazaki fragments that are later ligated together. DNA polymerase also has a proofreading function.
- DNA damage can occur from chemicals, radiation, and replication errors but cells have multiple repair mechanisms like base excision repair, nucleotide excision repair, and
DNA replication involves the synthesis of daughter DNA strands using parental DNA as a template. It occurs through a semi-conservative process whereby each new DNA molecule contains one original and one newly synthesized strand. Replication is bidirectional, with replication forks moving in opposite directions from an origin of replication. The leading strand is synthesized continuously while the lagging strand involves the discontinuous synthesis of Okazaki fragments. DNA polymerases and other proteins such as helicases, primases, ligases and topoisomerases work together to facilitate the replication process.
DNA replication occurs semi-conservatively, with each parental strand serving as a template for synthesis of a new complementary strand. This results in two identical DNA molecules, each with one original parental strand and one newly synthesized strand. Replication is initiated at the origin of replication and proceeds bidirectionally around the circular bacterial chromosome. Enzymes such as helicase unwind the parental DNA, topoisomerases relieve supercoiling, and DNA polymerase adds complementary nucleotides using the parental strands as templates.
DNA replication is semi-conservative and involves many enzymes. It begins at a replication origin where the DNA unwinds. RNA primers are added and DNA polymerase adds nucleotides to the 3' end of the primers to synthesize new DNA strands. The leading strand is synthesized continuously while the lagging strand is synthesized in fragments that are later joined. Transcription and translation then convert gene information into proteins.
A reaction in which daughter DNAs are synthesized using the parental DNAs as the template.
Transferring the genetic information to the descendant generation with a high fidelity
Semi-conservative replication
Bidirectional replication
Semi-continuous replication
High fidelity
Replication starts from unwinding the dsDNA at a particular point (called origin), followed by the synthesis on each strand.
The parental dsDNA and two newly formed dsDNA form a Y-shape structure called replication fork.
This document summarizes DNA replication. It begins by listing the objectives of describing the process. DNA replication duplicates the entire genome before cell division so each daughter cell receives a complete copy. It proceeds in a semi-conservative, bidirectional manner starting from the origin. Several enzymes are involved including helicase, DNA polymerase, primase, ligase and topoisomerases. DNA polymerase builds new strands using the old strands as templates while primase lays down RNA primers. The leading strand is synthesized continuously but the lagging strand requires discontinuous Okazaki fragments joined by ligase. Proofreading ensures high fidelity through exonuclease activity. Eukaryotes differ in having multiple origins and using RNAse H to remove primers.
This document provides an overview of gene expression and DNA replication. It discusses:
1) Gene expression in prokaryotes, which linearly transfers genetic information from DNA to mRNA to protein.
2) Additional complexities in eukaryotic gene expression, including intron splicing, adding a 5' cap and 3' poly-A tail to mRNA.
3) DNA replication, which uses the original DNA as a template to copy its sequence accurately via semi-conservative replication before cell division. DNA polymerase synthesizes new DNA in the 5' to 3' direction, creating leading and lagging strands.
- DNA replication involves unwinding the DNA double helix at the replication fork and using each single strand as a template to build new complementary strands in a semi-conservative manner, where each new double helix contains one original and one new strand.
- Replication proceeds bidirectionally from an origin of replication as the replication fork moves along the DNA in both directions. The leading strand is synthesized continuously while the lagging strand is synthesized discontinuously in fragments called Okazaki fragments.
- Several DNA polymerases and other proteins work together accurately and efficiently to copy the billions of bases in human DNA within a few hours during cell division.
The document provides an overview of the history and process of DNA replication. Some key points include:
- Early scientists thought protein was the genetic material, but experiments showed DNA was responsible for transformation and inheritance of traits.
- The structure of DNA was discovered in the 1950s by Watson and Crick based on Rosalind Franklin's X-ray crystallography photos, revealing the double helix structure with bases pairing on the inside.
- DNA replication involves unwinding the double helix at origins of replication, synthesizing new strands in opposite directions using DNA polymerase and RNA primers, and joining fragments on the lagging strand. This semiconservative process produces two DNA molecules, each with one original and
This document discusses various enzymes used for gene cloning. It describes restriction endonucleases that cut DNA at specific recognition sequences, leaving sticky or blunt ends. DNA ligase joins compatible DNA ends. DNA polymerases synthesize new DNA strands. Other enzymes mentioned include DNA modifying enzymes, topoisomerases, and enzymes for tailing DNA ends. The document provides examples of various restriction enzymes and their recognition sequences. It explains how enzymes are used in gene cloning techniques.
How does DNA replicate itself to form your genes...Sithembiso
DNA replication: The double helix is un'zipped' and unwound, then each separated strand (turquoise) acts as a template for replicating a new partner strand (green). Nucleotides (bases) are matched to synthesize the new partner strands into two new double helices.
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. This process occurs in all living organisms and is the basis for biological inheritance. The cell possesses the distinctive property of division, which makes replication of DNA essential..
The document discusses DNA replication in prokaryotes and eukaryotes. It explains that replication involves initiation at an origin of replication, followed by unwinding of the DNA double helix by helicase. RNA primers are synthesized by primase and DNA polymerase adds nucleotides to the primers to elongate DNA strands. In prokaryotes, leading and lagging strands are synthesized continuously and discontinuously respectively to form Okazaki fragments. Enzymes like DNA polymerase, ligase, and topoisomerase ensure high fidelity and processivity of replication. Telomerase maintains telomere integrity in eukaryotes during DNA replication.
DNA structure replication transcription translationAman Ullah
DNA is made up of four nucleotides that form a double helix structure. Watson and Crick discovered that DNA replicates in a semi-conservative manner, with each new DNA molecule composed of one original strand and one newly synthesized strand. DNA replication is highly regulated and involves several enzymes that unwind, proofread, and repair the DNA to replicate it with high fidelity. The information stored in DNA is used to direct the synthesis of proteins according to the central dogma of biology, with DNA being transcribed into RNA which is then translated into proteins.
Dna replication and enzymes involved in dna replicationNarayan Prahlad
DNA replication is the process by which DNA copies itself. It requires DNA polymerase enzymes, primers, and deoxynucleotide triphosphates. DNA polymerase adds nucleotides to the 3' end of the primer according to the DNA template. Replication occurs through the coordinated action of helicase, DNA polymerase, primase, ligase, and other proteins. DNA polymerase proofreads newly synthesized DNA to ensure high fidelity. The coordinated actions of these enzymes and proteins precisely duplicate the genome during semi-conservative replication.
DNA replication in prokaryotes occurs through a semi-conservative process whereby the parental DNA strands serve as templates for the production of new daughter strands. It begins with the unwinding of DNA at the origin of replication by helicase to form a replication fork. Primase then synthesizes an RNA primer to initiate leading and lagging strand DNA synthesis by DNA polymerase. While the leading strand is synthesized continuously, the lagging strand involves the formation of Okazaki fragments that are later joined by ligase. Polymerases also proofread and correct any errors to maintain high-fidelity replication. Replication terminates when the replication forks from opposite directions meet.
Similar to Cytogenetics 2 replication, transcription and translation (20)
3. Proposed Models of DNA Replication
• In the late 1950s, three different mechanisms
were proposed for the replication of DNA
– Conservative model
• Both parental strands stay together after DNA replication
– Semi-conservative model
• The double-stranded DNA contains one parental and one
daughter strand following replication
– Dispersive model
• Parental and daughter DNA are interspersed in both strands
following replication
Dr. SAHAR ABO ELFADL 3
4. Three models for DNA replication
The most accepted
Dr. SAHAR ABO ELFADL 4
5. Directionality of DNA
PO4 nucleotide
• You need to
number the
carbons! N base
– it matters!
5′ CH2
This will be O
IMPORTANT!!
4′ ribose 1′
3′ 2′
OH
Dr. SAHAR ABO ELFADL 5
6. The DNA backbone 5′
PO4
• Putting the DNA base
5′ CH2
backbone together O
– refer to the 3′ and 5′ ends 4′
C
1′
of the DNA 3′ 2′
O
• the last trailing carbon –
O P O
Sounds trivial, but…
O base
this will be 5′ CH2
IMPORTANT!! O
4′ 1′
3′ 2′
OH
Dr. SAHAR ABO ELFADL 6 3′
7. Anti-parallel strands
• Nucleotides in DNA
backbone are bonded from
phosphate to sugar
5′ 3′
between 3′ & 5′ carbons
– DNA molecule has “direction”
– complementary strand runs in
opposite direction
Dr. SAHAR ABO ELFADL 7 3′ 5′
8. Bonding in DNA
hydrogen
bonds
5′ 3′
covalent
phosphodiester
bonds
3′
5′
….strong or weak bonds?
Dr. SAHAR ABO ELFADL 8
How do the bonds fit the mechanism for copying DNA?
9. Copying DNA
• Replication of DNA
– base pairing allows
each strand to serve as
a template for a new
strand
– new strand is 1/2
parent template &
1/2 new DNA (semi-
conservative).
Dr. SAHAR ABO ELFADL 9
10. DNA Replication Let’s meet
the team…
• Large team of enzymes coordinates replication
Dr. SAHAR ABO ELFADL 10
11. Replication: 1st step
• Unwind DNA
– helicase enzyme
• unwinds part of DNA helix
• stabilized by single-stranded binding proteins
helicase
single-stranded binding proteins ABO ELFADL replication fork
Dr. SAHAR 11
12. Replication: 2nd step
Build daughter DNA
strand
add new
complementary bases
DNA polymerase III
But…
Where’s the
We’re missing
ENERGY
DNA something!
for the bonding!
Polymerase III What?
Dr. SAHAR ABO ELFADL 12
13. Energy of Replication
Where does energy for bonding usually come from?
We come
with our own
energy!
You
remember energy
ATP!
Are there
other ways
to get energy
out of it?
And we
leave behind a
GTP
TTP
ATP nucleotide! TMP
GMP
AMP
ADP
modified nucleotide ELFADL
Dr. SAHAR ABO 13
14. Okazaki
Leading & Lagging strands
Limits of DNA polymerase III
can only build onto FREE 3′
end of an existing DNA 5′
ents
3′
strand Okaza
ki fragm
5′
3′
5′
3′ 5′ 5′
3′
Lagging strand
ligase
growing 3′
replication fork
5′
Leading strand
Lagging strand
3′ 5′
3′
DNA polymerase III
Okazaki fragments
joined by ligase Leading strand
Dr. SAHAR ABO ELFADL 14
“spot welder” enzyme continuous synthesis
15. Replication fork / Replication
5′
bubble
3′
5′ 3′
DNA polymerase III
leading strand
5′
3′ 3′ 5′
5′ 5′
5′ 3′ 3′
lagging strand
3′ 5′
5′
3′ lagging strand leading strand
5′ growing
3′ replication fork 5′
5′ growing
replication fork 5′
leading strand 3′
lagging strand
3′
5′
5′ 5′
Dr. SAHAR ABO ELFADL 15
16. Starting DNA synthesis: RNA primers
Limits of DNA polymerase III
can only build onto 3′ end of
an existing DNA strand 5′
3′ 5′ 3′
5′
3′
3′ 5′
growing 3′ primase
replication fork DNA polymerase III
5′
RNA 5′
RNA primer 3′
built by primase
serves as starter sequence
for DNA polymerase SAHAR ABO ELFADL
Dr. III 16
17. Replacing RNA primers with DNA
DNA polymerase I
removes sections of RNA DNA polymerase I
primer and replaces with 5′
DNA nucleotides 3′
3′
5′ ligase
growing 3′
replication fork
5′
RNA 5′
3′
But DNA polymerase I still
can only build onto 3′ end of
Dr. SAHAR ABO ELFADL
an existing DNA strand 17
18. Houston, we
Chromosome erosion have a problem!
All DNA polymerases can
only add to 3′ end of an DNA polymerase I
existing DNA strand 5′
3′
3′
5′
growing 3′
replication fork DNA polymerase III
5′
RNA 5′
Loss of bases at 5′ ends 3′
in every replication
chromosomes get shorter with each replication
Dr. SAHAR ABO ELFADL 18
limit to number of cell divisions?
19. Telomeres
Repeating, non-coding sequences at the end
of chromosomes = protective cap
5′
limit to ~50 cell divisions
3′
3′
5′
growing 3′ telomerase
replication fork
5′
5′
Telomerase
TTAAGGG TTAAGGG TTAAGGG
enzyme extends telomeres 3′
can add DNA bases at 5′ end
different level of activity in different cells
Dr. SAHAR ABO ELFADL 19
high in stem cells & cancers -- Why?
20. Replication fork
DNA
polymerase III lagging strand
DNA
polymerase I
3’
Okazaki primase
fragments 5’
5’ ligase
SSB
3’ 5’
3’ helicase
DNA
polymerase III
5’ leading strand
3’
direction of replication
Dr. SAHAR ABO ELFADL 20
SSB = single-stranded binding proteins
21. Fast & accurate!
Human cell
• copies its 6 billion
bases
• Completes mitosis in
only few hours
• remarkably accurate
• only ~1 error per 100
million bases
• ~30 errors per cell cycle
Dr. SAHAR ABO ELFADL 21
22. NOW
Let us see together this video about
DNA REPLICATION
Dr. SAHAR ABO ELFADL 22
23. DNA Replication
• Origins of replication
1. Replication Forks: hundreds of Y-shaped
Forks
regions of replicating DNA molecules
where new strands are growing.
3’
5’ Parental DNA Molecule Replication
Fork
3’
Dr. SAHAR ABO ELFADL 23
5’
24. DNA Replication
• Origins of replication
2. Replication Bubbles:
Bubbles
a. Hundreds of replicating bubbles
(Eukaryotes).
(Eukaryotes)
b. Single replication fork (bacteria).
Bubbles Bubbles
Dr. SAHAR ABO ELFADL 24
25. DNA Replication
• Strand Separation:
Separation
1. Helicase: enzyme which catalyze the
Helicase
unwinding and separation (breaking H-
Bonds) of the parental double helix.
2. Single-Strand Binding Proteins: proteins
Proteins
which attach and help keep the separated
strands apart.
Dr. SAHAR ABO ELFADL 25
26. DNA Replication
• Priming:
1. RNA primers: before new DNA strands can
primers
form, there must be small pre-existing
primers (RNA) present to start the addition of
new nucleotides (DNA Polymerase).
Polymerase)
2. Primase: enzyme that polymerizes
Primase
(synthesizes) the RNA Primer.
Dr. SAHAR ABO ELFADL 26
27. DNA Replication
• Synthesis of the new DNA Strands:
1. DNA Polymerase: with a RNA primer in
Polymerase
place, DNA Polymerase (enzyme) catalyze
the synthesis of a new DNA strand in the 5’
to 3’ direction.
direction
5’ 3’
RNA
5’
DNA Polymerase Primer
Nucleotide Dr. SAHAR ABO ELFADL 27
28. DNA Replication
2. Leading Strand: synthesized as a
Strand
single polymer in the 5’ to 3’ direction.
direction
5’ 3’
5’
RNA
Nucleotides DNA Polymerase Primer
Dr. SAHAR ABO ELFADL 28
29. DNA Replication
3. Lagging Strand: also synthesized in
Strand
the 5’ to 3’ direction, but discontinuously
direction
against overall direction of replication.
Leading Strand
5 3’
’
3’ 5’
DNA Polymerase RNA Primer
5’ 3’
3’ 5’
Lagging Strand
Dr. SAHAR ABO ELFADL 29
30. DNA Replication
4. Okazaki Fragments: series of short
Fragments
segments on the lagging strand.
Okazaki Fragment
Okazaki Fragment
DNA
Polymerase
RNA
Primer
5’ 3’
3’ 5’
Lagging Strand
Dr. SAHAR ABO ELFADL 30
31. DNA Replication
5. DNA ligase: a linking enzyme that
ligase
catalyzes the formation of a covalent bond
from the 3’ to 5’ end of joining stands.
Example: joining two Okazaki fragments together.
DNA ligase
Okazaki Fragment 1 Okazaki Fragment 2
5’ 3’
3’ Lagging Strand Dr. SAHAR ABO ELFADL
5’
31
33. The Link Between DNA and
Protein
• DNA contains the molecular blueprint of
every cell
• Proteins are the “molecular workers” of the
cell
• Proteins control cell shape, function,
reproduction, and synthesis of biomolecules
• The information in DNA genes must
therefore be linked to the proteins that run
the cell
Dr. SAHAR ABO ELFADL 33
34. Transcription
• Process by which
genetic information Translation
encoded in DNA is • Process by which
copied onto information encoded
messenger RNA in mRNA is used to
• Occurs in the nucleus assemble a protein at
• DNA mRNA a ribosome
• Occurs on a
Ribosome
• mRNA protein
Dr. SAHAR ABO ELFADL 34
35. Three Types of RNA
mRNA
A
A
A
A
U
U
U
U
U
U
U
U
messenger G GC G G GG
catalytic site
Large
subunit
rRNA 1 2
ribosomal
Small
subunit tRNA docking sites
Met
tRNA Attached amino acid
transfer
A
anticodon
Dr. SAHAR ABO ELFADL 35
G
U
36. Transcription and Translation
• DNA directs protein synthesis in a two-
step process
1. Information in a DNA gene is copied into
mRNA in the process of transcription
2. mRNA, together with tRNA, amino acids,
and a ribosome, synthesize a protein in
the process of translation
Dr. SAHAR ABO ELFADL 36
37. Information
Flow:
DNA
RNA
Protein
Dr. SAHAR ABO ELFADL 37
38. The Genetic Code
• The base sequence in a DNA gene
dictates the sequence and type of amino
acids in translation
• Bases in mRNA are read by the ribosome
in triplets called codons
• Each codon specifies a unique amino acid
in the genetic code
• Each mRNA also has a start and a stop
codon
Dr. SAHAR ABO ELFADL 38
40. Overview of Transcription
• Transcription of a
DNA gene into RNA
has three stages
– Initiation
– Elongation
– Termination
Dr. SAHAR ABO ELFADL 40
41. Initiation
• Initiation phase of transcription
1. DNA molecule is unwound and strands are
separated at the beginning of the gene
sequence
2. RNA polymerase binds to promoter
region at beginning of a gene on template
strand
Dr. SAHAR ABO ELFADL 41
43. Elongation
1. RNA polymerase synthesizes a sequence
of RNA nucleotides along DNA template
strand
2. Bases in newly synthesized RNA strand
are complementary to the DNA template
strand
3. RNA strand peels away from DNA
template strand as DNA strands repair
and wind up
Dr. SAHAR ABO ELFADL 43
45. Elongation
• As elongation proceeds, one end of the
RNA drifts away from the DNA; RNA
polymerase keeps the other end
temporarily attached to the DNA
template strand
Dr. SAHAR ABO ELFADL 45
50. mRNA
– The DNA is in the nucleus and the ribosomes
are in the cytoplasm
– The genes that encode the proteins for a
biochemical pathway are not clustered together
on the same chromosome
Each gene consists of multiple segments of
DNA that encode for protein, called exons
Exons are interrupted by other segments that
are not translated, called introns
Dr. SAHAR ABO ELFADL 50
51. DNA exons
introns
promoter
Transcription from DNA to RNA
Initial
transcript
s
Splicing In tron ut
so
ped ut
it n
snnpro d o
I pe
completed
snip
mRNA transcript Dr. SAHAR ABO ELFADL 51
52. mRNA
– Transcription of a gene produces a very
long RNA strand that contains introns
and exons
– Enzymes in the nucleus cut out the
introns and splice together the exons to
make true mRNA
– mRNA exits the nucleus through a
membrane pore and associates with a
ribosome
Dr. SAHAR ABO ELFADL 52
53. Ribosomes
• Ribosomes are large complexes of
proteins and rRNA
Dr. SAHAR ABO ELFADL 53
54. Ribosomes
• Ribosomes are composed of two
subunits
– Small subunit has binding sites for mRNA
and a tRNA
– Large subunit has binding sites for two
tRNA molecules and catalytic site for
peptide bond formation
Dr. SAHAR ABO ELFADL 54
55. Transfer RNAs
• Transfer RNAs hook up to and bring amino
acids to the ribosome
• There is at least one type of tRNA assigned
to carry each of the twenty different amino
acids
• Each tRNA has three exposed bases called
an anticodon
• The bases of the tRNA anticodon pair with
an mRNA codon within a ribosome binding
site
Dr. SAHAR ABO ELFADL 55
56. Translation
• Ribosomes, tRNA, and mRNA
cooperate in protein synthesis, which
begins with initiation:
1. The mRNA binds to the small ribosomal
subunit
2. The mRNA slides through the subunit
until the first AUG (start codon) is
exposed in the first tRNA binding site…
Dr. SAHAR ABO ELFADL 56
57. Translation
3. The first tRNA carrying methionine (and
anticodon UAC) binds to the mRNA start
codon completing the initiation
complex
4. The large ribosomal subunit joins the
complex
Dr. SAHAR ABO ELFADL 57
58. Translation:Initiation (1)
A tRNA with an
attached methionine
amino acid binds to a
small ribosomal
subunit, forming an
initiation complex.
Dr. SAHAR ABO ELFADL 58
59. Translation:Initiation (2)
The initiation
complex binds to
end of mRNA and
travels down until it
encounters an AUG
codon in the mRNA.
The anticodon of the
tRNA in the initiation
complex forms base
pairs with the AUG
codon.
Dr. SAHAR ABO ELFADL 59
60. Translation:Initiation (3)
The large
ribosomal subunit
binds to the small
subunit, with the
mRNA between the
two subunits.
The methionine
tRNA is in the first
tRNA site on the
large subunit.
Dr. SAHAR ABO ELFADL 60
61. Translation:Elongation 1
The second tRNA enters the
second tRNA site on the large
ribosomal subunit.
Which tRNA binds depends
on the ability of its anticodon
(CAA in this example) to base
pair with the codon (GUU in
this example) in the mRNA.
tRNAs with a CAA anticodon
carry an attached valine
amino acid, which was added
to it by enzymes in the
cytoplasm.
Dr. SAHAR ABO ELFADL 61
62. Translation:Elongation 2
The "empty" tRNA is
released and the ribosome
moves down the mRNA,
one codon to the right.
The tRNA that is attached
to the two amino acids is
now in the first tRNA
binding site and the
second tRNA binding site
is empty.
Dr. SAHAR ABO ELFADL 62
63. Translation:Elongation 3
The catalytic site on
the large subunit
catalyzes the
formation of a peptide
bond linking the amino
acids methionine to
valine.
The two amino acids
are now attached to
the tRNA in the
second binding
position.
Dr. SAHAR ABO ELFADL 63
64. Translation:Elongation 4
Another tRNA enters the
second tRNA binding site
carrying its attached
amino acid.
The tRNA has an
anticodon that pairs with
the codon. (Here, the CAU
mRNA codon pairs with a
GUA tRNA anticodon.)
The tRNA molecule carries
the amino acid histidine
(his).
Dr. SAHAR ABO ELFADL 64
65. Translation:Elongation 5
Binding of tRNAs, &
formation of peptide
bonds continues.
Ribosome reaches
STOP codon (UAG).
Protein "release
factors" signal the
ribosome to release
the protein.
The mRNA is also
released and large &
small subunits
Dr. SAHAR ABO ELFADL
separate.
65
66. Translation:Termination
The catalytic site forms
a new peptide bond, in
this example, between
the valine and the
histidine.
A three-amino acid
chain is now attached
to the tRNA in the
second tRNA binding
site.
The empty tRNA in the
first site is released
and the ribosome
Dr. SAHAR ABO ELFADL
moves one codon to
66
the right.
67. Complementary Base Pairing
gene
(a) complementary C
etc.
T
T
T
A
A
DNA strand G G G G G
template
C C C C C
A
A
A
C C C C C
T
G
T
T
DNA strand etc.
codons
G
G G
G G
G G
G G
G
(b) mRNA C
C
A
A
U
U
U
U
U
U
etc.
U anticodons
C
C
C
C
(c) tRNA A A
C
C
U
U etc.
A
C
C
amino acids
Dr. SAHAR ABO ELFADL 67
(d) protein Methionine Glycine Valine etc.
69. Effects of Mutations on Proteins
• Recall that mutations are changes in
the base sequence of DNA
• Most mutations are categorized as
– Substitutions
– Deletions
– Insertions
– Inversions
– Translocations
Dr. SAHAR ABO ELFADL 69
70. Effects of Mutations on Proteins
• Inversions and translocations
– When pieces of DNA are broken apart
and reattached in different orientation or
location
– Not problematic if entire gene is moved
– If gene is split in two it will no longer code
for a complete, functional protein
Dr. SAHAR ABO ELFADL 70
71. Effects of Mutations on Proteins
• Insertions or deletions
– Nucleotides are added or subtracted from
a gene
– Reading frame of RNA codons is
changed
• THEDOGSAWTHECAT is changed by
deletion of the letter “S” to
THEDOGAWTHECAT
– Resultant protein has very different amino
acid sequence; almost always is non-
functional
Dr. SAHAR ABO ELFADL 71
72. Effects of Mutations on
Proteins
• Nucleotide substitutions (point
mutations)
– An incorrect nucleotide takes the place of
a correct one
– Protein structure and function is
unchanged because many amino acids
are encoded by multiple codons
– Protein may have amino acid changes
that are unimportant to function (neutral
mutations)
Dr. SAHAR ABO ELFADL 72
73. Effects of Mutations on
Proteins
• Effects of nucleotide substitutions
– Protein function is changed by an altered
amino acid sequence (as in gly val in
hemoglobin in sickle cell anemia)
– Protein function is destroyed because
DNA mutation creates a premature stop
codon
Dr. SAHAR ABO ELFADL 73
75. Mutations Fuel Evolution
• Mutations are heritable changes in the DNA
• Approx. 1 in 105-106 eggs or sperm carry a
mutation
• Most mutations are harmful or neutral
• Mutations create new gene sequences and
are the ultimate source of genetic variation
• Mutant gene sequences that are beneficial
may spread through a population and become
common
Dr. SAHAR ABO ELFADL 75
76. How Are Genes Regulated?
• The human genome contains ~ 30,000
genes
• A given cell “expresses” (transcribes)
only a small number of genes
• Some genes are expressed in all cells
• Other genes are expressed only
– In certain types of cells
– At certain times in an organism’s life
– Under specific environmental conditions
Dr. SAHAR ABO ELFADL 76
Enzymes more than a dozen enzymes & other proteins participate in DNA replication
09/29/12
09/29/12
09/29/12
09/29/12
09/29/12
09/29/12
09/29/12
09/29/12
09/29/12
09/29/12 Figure: 10.2 Title: Cells synthesize three major types of RNA Caption: RNA consists of a single nucleotide strand whose bases are complementary to the bases within the template strand of the gene. There are three major types of RNA: (a) Messenger RNA (mRNA) carries within its base sequence the information for the amino acid sequence of a protein. (b) Ribosomes contain both ribosomal RNA (rRNA) and proteins. The ribosome is divided into a small and large subunit that join together during protein synthesis. The small subunit binds the mRNA; the large subunit binds tRNA and catalyzes the formation of bonds between amino acids to form a protein. (c) One side of transfer RNA contains an anticodon, which is a sequence of three nucleotides that can form base pairs with a codon in mRNA. Enzymes within the cytoplasm attach a specific amino acid to the opposite side of the tRNA so that it can carry the proper amino acid to the ribosome for incorporation into a new protein.
09/29/12 Figure: 10.3 Title: Genetic information flows from DNA to RNA to protein Caption: Cellular information is stored within the base sequence of DNA. Transcription, the process of RNA synthesis, occurs in the nucleus. During transcription, the nucleotide sequence in a gene specifies the nucleotide sequence in a complementary RNA molecule. For protein-encoding genes, the product is an mRNA molecule that exits from the nucleus and enters the cytoplasm where translation occurs. During translation, the sequence in an mRNA molecule specifies the amino acid sequence in a protein.
Table 10-3 The Genetic Code (Codons of mRNA)
FIGURE 10-4a Transcription is the synthesis of RNA from instructions in DNA A gene is a segment of a chromosome's DNA. One of the DNA strands will serve as the template for the synthesis of an RNA molecule with bases complementary to the bases in the DNA strand.
FIGURE 10-4b Transcription is the synthesis of RNA from instructions in DNA A gene is a segment of a chromosome's DNA. One of the DNA strands will serve as the template for the synthesis of an RNA molecule with bases complementary to the bases in the DNA strand.
FIGURE 10-5 RNA transcription in action This colorized electron micrograph shows the progress of RNA transcription in the egg of an African clawed toad. In each treelike structure, the central "trunk" is DNA (blue) and the "branches" are RNA molecules (red). A series of RNA polymerase molecules (too small to be seen in this micrograph) are traveling down the DNA, synthesizing RNA as they go. The beginning of the gene is on the left. The short RNA molecules on the left have just begun to be synthesized; the long RNA molecules on the right are almost finished.
FIGURE 10-4c Transcription is the synthesis of RNA from instructions in DNA A gene is a segment of a chromosome's DNA. One of the DNA strands will serve as the template for the synthesis of an RNA molecule with bases complementary to the bases in the DNA strand.
FIGURE 10-4d Transcription is the synthesis of RNA from instructions in DNA A gene is a segment of a chromosome's DNA. One of the DNA strands will serve as the template for the synthesis of an RNA molecule with bases complementary to the bases in the DNA strand.
09/29/12 Figure: 10.E4 Title: Eukaryotic genes contain introns and exons Caption: Eukaryotic genes contain introns and exons
09/29/12 Figure: 19-2 part a Title: Viral structure and replication part a Caption: (a) A cross section of the virus that causes AIDS. Inside, genetic material is surrounded by a protein coat and molecules of reverse transcriptase, an enzyme that catalyzes the transcription of DNA from the viral RNA template after the virus enters the host cell. This virus is among those that also have an outer envelope that is formed from the host cell's plasma membrane. Spikes made of glycoprotein (protein and carbohydrate) project from the envelope and help the virus attach to its host cell.
09/29/12 Figure: 19-2 part a Title: Viral structure and replication part a Caption: (a) A cross section of the virus that causes AIDS. Inside, genetic material is surrounded by a protein coat and molecules of reverse transcriptase, an enzyme that catalyzes the transcription of DNA from the viral RNA template after the virus enters the host cell. This virus is among those that also have an outer envelope that is formed from the host cell's plasma membrane. Spikes made of glycoprotein (protein and carbohydrate) project from the envelope and help the virus attach to its host cell.
09/29/12 Figure: 10.6abc Title: Initiation of protein synthesis Caption: Initiation of protein synthesis
09/29/12 Figure: 10.6def Title: Elongation during protein synthesis Caption: Elongation during protein synthesis
09/29/12 Figure: 10.6ghi Title: Termination of protein synthesis Caption: Termination of protein synthesis
09/29/12 Figure: 10.7 Title: Complementary base pairing is critical at each step in decoding genetic information Caption: (a) DNA contains two strands: the template strand is used by RNA polymerase to synthesize an RNA molecule; the other strand, which is complementary to the template strand, is needed for DNA replication. (b) Bases in the template strand of DNA are transcribed into a complementary mRNA. Codons are sequences of three bases that specify an amino or a stop during protein synthesis. (c) Unless it is a stop codon, each mRNA codon forms base pairs with the anticodon of a tRNA molecule that carries a specific amino acid. (d) The ribosome links the amino acids together, forming the protein.
Table 10-4 Effects of Mutations in the Hemoglobin Gene