This document provides an overview of DNA and genetics. It discusses how DNA was established as the genetic material through experiments in the 1940s-1950s, including Griffith's transformation experiments, Avery et al.'s work demonstrating the transforming principle was DNA, and Hershey and Chase's experiments with bacterial viruses. It also summarizes the discovery of the DNA double helix structure by Watson and Crick in 1953, based on Chargaff's rules and X-ray crystallography data. The key properties of DNA structure, including specific base pairing and semiconservative replication, are briefly outlined.
Frederick Griffith discovered a "transforming principle" in 1928 when live S strain bacteria developed in mice injected with a mixture of heat-killed S strain and live R strain bacteria. Later, Avery, MacLeod and McCarty determined that this transforming principle was DNA through experiments treating bacteria with enzymes that broke down DNA, RNA, and proteins. In 1952, Hershey and Chase conclusively showed through experiments with radioactive labeling of bacteriophages that DNA is the genetic material transferred from viruses to bacteria during infection, not proteins.
Frederick Griffith conducted experiments in 1928 using two strains of Streptococcus pneumoniae bacteria - R strain bacteria that were harmless, and S strain bacteria that were virulent and caused pneumonia. When Griffith combined heat-killed S bacteria with live R bacteria and injected them into mice, the mice unexpectedly developed pneumonia and died, with their blood containing live S bacteria. Griffith concluded the R bacteria must have taken on a "transforming principle" from the S bacteria that allowed them to become virulent. In 1944, Avery, McCarty and MacLeod purified this principle from heat-killed S cells and determined through various tests that it was DNA. However, debate continued until 1952 when Hershey and Chase conclusively identified DNA
Hershey and Chase conducted an experiment in 1952 using bacteriophages (viruses that infect bacteria) to determine whether DNA or protein is the genetic material. They labeled phage particles with either radioactive phosphorus or sulfur and allowed them to infect E. coli bacteria. They found that the radioactive phosphorus from the DNA entered the bacterial cells and was incorporated into the next generation of phages, while the radioactive sulfur from the protein coat did not. This established that DNA, not protein, carries the genetic information required for reproduction.
The document discusses evidence that DNA is the genetic material:
1) Griffith's experiment showed bacterial transformation from non-virulent to virulent strains upon uptake of DNA from heat-killed bacteria.
2) Avery, MacLeod and McCarty's experiment showed transformation only occurred when DNA was present, as DNase treatment prevented transformation.
3) Hershey and Chase's experiment using radioactive labels showed that only bacteriophage DNA, not protein, entered bacteria to produce new phage particles.
The document summarizes several key experiments that helped establish DNA as the genetic material:
- Griffith's experiment showed a "transforming principle" in dead bacteria could change live bacteria;
- Avery, McCarty and MacLeod purified and identified this principle as DNA;
- Hershey and Chase showed that DNA, not protein, was injected by viruses into infected bacteria;
- Fraenkel-Conrat's experiment proved that RNA could also act as genetic material.
Rosalind Franklin's X-ray crystallography work provided evidence of DNA's double-helix structure, though she did not receive full credit due to gender biases of the time.
Frederick Griffith's experiments in 1928 showed that a transforming principle could pass from dead virulent pneumonia bacteria to live avirulent bacteria, making them deadly. Oswald Avery later purified this principle and through chemical and enzymatic tests determined it was DNA, not protein as previously believed. In 1952, Hershey and Chase used radioactive labeling to track the entry of DNA and proteins from bacteriophages into infected bacteria. They found that only the labeled DNA entered the bacterial cells, providing definitive evidence that DNA is the genetic material.
DNA as a Genetic Material - Dr. P. Saranraj, Assistant Professor, Department of Microbiology, Sacred Heart College (Autonomous), Tirupattur, Vellore District, Tamil Nadu, India.
Frederick Griffith discovered a "transforming principle" in 1928 when live S strain bacteria developed in mice injected with a mixture of heat-killed S strain and live R strain bacteria. Later, Avery, MacLeod and McCarty determined that this transforming principle was DNA through experiments treating bacteria with enzymes that broke down DNA, RNA, and proteins. In 1952, Hershey and Chase conclusively showed through experiments with radioactive labeling of bacteriophages that DNA is the genetic material transferred from viruses to bacteria during infection, not proteins.
Frederick Griffith conducted experiments in 1928 using two strains of Streptococcus pneumoniae bacteria - R strain bacteria that were harmless, and S strain bacteria that were virulent and caused pneumonia. When Griffith combined heat-killed S bacteria with live R bacteria and injected them into mice, the mice unexpectedly developed pneumonia and died, with their blood containing live S bacteria. Griffith concluded the R bacteria must have taken on a "transforming principle" from the S bacteria that allowed them to become virulent. In 1944, Avery, McCarty and MacLeod purified this principle from heat-killed S cells and determined through various tests that it was DNA. However, debate continued until 1952 when Hershey and Chase conclusively identified DNA
Hershey and Chase conducted an experiment in 1952 using bacteriophages (viruses that infect bacteria) to determine whether DNA or protein is the genetic material. They labeled phage particles with either radioactive phosphorus or sulfur and allowed them to infect E. coli bacteria. They found that the radioactive phosphorus from the DNA entered the bacterial cells and was incorporated into the next generation of phages, while the radioactive sulfur from the protein coat did not. This established that DNA, not protein, carries the genetic information required for reproduction.
The document discusses evidence that DNA is the genetic material:
1) Griffith's experiment showed bacterial transformation from non-virulent to virulent strains upon uptake of DNA from heat-killed bacteria.
2) Avery, MacLeod and McCarty's experiment showed transformation only occurred when DNA was present, as DNase treatment prevented transformation.
3) Hershey and Chase's experiment using radioactive labels showed that only bacteriophage DNA, not protein, entered bacteria to produce new phage particles.
The document summarizes several key experiments that helped establish DNA as the genetic material:
- Griffith's experiment showed a "transforming principle" in dead bacteria could change live bacteria;
- Avery, McCarty and MacLeod purified and identified this principle as DNA;
- Hershey and Chase showed that DNA, not protein, was injected by viruses into infected bacteria;
- Fraenkel-Conrat's experiment proved that RNA could also act as genetic material.
Rosalind Franklin's X-ray crystallography work provided evidence of DNA's double-helix structure, though she did not receive full credit due to gender biases of the time.
Frederick Griffith's experiments in 1928 showed that a transforming principle could pass from dead virulent pneumonia bacteria to live avirulent bacteria, making them deadly. Oswald Avery later purified this principle and through chemical and enzymatic tests determined it was DNA, not protein as previously believed. In 1952, Hershey and Chase used radioactive labeling to track the entry of DNA and proteins from bacteriophages into infected bacteria. They found that only the labeled DNA entered the bacterial cells, providing definitive evidence that DNA is the genetic material.
DNA as a Genetic Material - Dr. P. Saranraj, Assistant Professor, Department of Microbiology, Sacred Heart College (Autonomous), Tirupattur, Vellore District, Tamil Nadu, India.
Discovery of dna as the universal genetic materialRupal Agrawal
Gregor Mendel discovered genes in 1866. Friedrich Miescher isolated DNA in 1868. In the 1940s, Avery, MacLeod and McCarty conducted experiments showing that DNA is the genetic material. They found that only DNA from one type of pneumonia bacteria could transform another type of the bacteria. Similarly, Hershey and Chase showed in 1952 that when viruses infect bacteria, only the viral DNA, not proteins, enters the host cell, proving DNA is the genetic material in viruses too. These experiments established DNA as the universal genetic material.
1) Griffith discovered a "transforming principle" that allowed non-virulent bacteria to become virulent after exposure to heat-killed virulent bacteria.
2) Avery, MacLeod, and McCarty determined that the transforming principle was DNA through experiments treating components with DNAses, RNAses, and proteases.
3) Hershey and Chase provided definitive evidence that DNA is the genetic material through experiments using bacteriophages containing radioactive DNA or protein to infect bacteria, showing that only DNA was transferred.
Hershey and chase experiment-the blender experimentbiOlOgyBINGE
It was performed by Alfred Hershey and Martha Chase in 1952.
It led to confirmation of the genetic nature of DNA came from an experiment with E.coli phage T2.
for more details visit our youtube channel.
Frederick Griffith discovered the principle of transformation through experiments with Streptococcus pneumoniae bacteria. He found that heat-killed virulent S-strain bacteria could make non-virulent R-strain bacteria transform and become virulent. Later, Oswald Avery, Colin MacLeod and Maclyn McCarty discovered that DNA alone from S bacteria could transform R bacteria. Alfred Hershey and Martha Chase provided conclusive evidence that DNA, not protein, is the genetic material through experiments using bacteriophages infecting E. coli bacteria. They found that radioactive DNA, but not protein, passed from the bacteriophages into the bacterial cells.
Frederick Griffith discovered in 1928 that heat-killed bacteria contained a transforming factor that could change harmless bacteria into disease-causing bacteria. Oswald Avery and colleagues in 1944 determined that this transforming factor was DNA. Rosalind Franklin's x-ray crystallography work in 1952 provided evidence that DNA has a helical structure, which James Watson and Francis Crick used to propose their double helix model of DNA structure in 1953.
Transduction is a mode of genetic transfer between bacteria mediated by bacteriophages. During viral replication, fragments of bacterial DNA can become packaged within viral particles. These particles may then infect other bacteria and insert the donor DNA into the recipient genome. There are two types of transduction - generalized, where any bacterial DNA fragment can be transferred, and specialized, where only DNA near the site of viral integration is transferred. Cotransduction frequencies can also be used to map the relative locations of bacterial genes, as genes closer together are more likely to be cotransferred within the same viral particle. Transduction is useful for genetic engineering and mapping bacterial chromosomes.
The document summarizes the history of discoveries leading to the understanding that DNA is the molecule of heredity. It describes early experiments in the 1900s and 1920s by scientists like Griffith who found that traits could be transferred between bacteria. Further work by Avery in 1944 found that DNA was responsible for this transformation. Chargaff discovered proportional relationships between DNA bases within species. Experiments in the 1950s by Hershey and Chase and the work of Franklin, Wilkins, Watson and Crick ultimately revealed DNA's double helix structure and its role in storing and transmitting genetic information from parents to offspring.
The document provides a history of molecular biology, describing how it emerged from the union of biochemistry, genetics, microbiology, and virology in the 1930s. It summarizes several major discoveries and events, including identifying DNA as the genetic material in 1944, determining the double helix structure of DNA in 1953, cracking the genetic code in the 1960s, and using new technologies like X-ray crystallography to study macromolecules. The document traces how molecular biology aims to explain life at the molecular level starting from nucleic acids and proteins.
Lectut btn-202-ppt-l1. introduction and historical background part i (1)Rishabh Jain
1. In 1972, Paul Berg constructed the first recombinant DNA molecule in vitro by combining DNA from different organisms, marking the birth of recombinant DNA technology.
2. In 1973, Stanley Cohen and Herbert Boyer developed the first successful method of gene cloning by inserting the kanamycin resistance gene into a bacterial plasmid.
3. Recombinant DNA technology allows scientists to modify the genetic makeup of organisms and has led to important discoveries such as the production of human insulin in bacteria in 1982.
Genetic Engineering and the future of EvolutiomRicha Khatiwada
Genetic engineering will allow humans to direct their own evolution for the first time in history. By arranging the four bases of DNA - A, T, G, C - genetic instructions can be changed, altering organisms. CRISPR is a new, faster, cheaper, and more precise genetic engineering tool that can edit live cells and has reduced the cost of genetic engineering by 99%. If guided with caution, genetic engineering has the potential to cure diseases like HIV and cancer, extend human lifespans by borrowing genes from immortal species, and enhance humans for space travel by engineering plants and stronger bodies. However, there are also risks like the rise of "designer babies", dictators forcing genetic changes, and the creation of super soldiers
Horizantal gene transfer in evolution of nematodespriyank mhatre
This is a presentation on Horizontal gene transfer(HGT) in evolution of nematodes which gives us idea about importance of HGT in evolution of nematode parasitism. Here I have covered the historical events about HGT as well.
This is my First seminar in Div of Nematology.
This document discusses evidence that DNA is the genetic material that is passed from parents to offspring. It describes three key experiments:
1. Frederick Griffith's 1928 experiment on bacteria transformation showed that heat-killed bacteria could transfer genetic material to live bacteria.
2. Avery, Macleod, and McCarty's 1944 experiment purified the transforming material from Griffith's experiment and found that removal of proteins did not affect transformation, but DNA digestion did, proving DNA was the genetic material.
3. Hershey and Chase's 1952 experiment on bacteriophages, using radioactive labeling, showed that only DNA entered bacteria cells during infection, while proteins remained outside, proving DNA was the genetic material of phages.
This document discusses the Central Dogma of Biology and the discovery of DNA as the genetic material. It summarizes that:
1) Early experiments showed that chromosomes behaved like Mendel's hereditary factors and were linked to specific traits. The Hershey-Chase experiment provided definitive evidence that DNA, not protein, was the genetic material.
2) Watson and Crick discovered the double helix structure of DNA in 1953, explaining Chargaff's rules of base pairing. Semiconservative replication of DNA was demonstrated by Meselson and Stahl in 1957.
3) DNA replication requires several enzymes including DNA polymerase, helicase, ligase and primase to unwind and copy the DNA, adding
The document provides an overview of genetic engineering and its history. It discusses the basics of genetic engineering, which involves isolating and copying genetic material of interest using molecular cloning methods and inserting new DNA into the host genome. The history of genetic engineering is then explored, from early discoveries like Mendel's work with inheritance in peas to more modern developments like recombinant DNA techniques, PCR, and the creation of the first transgenic animal. A number of influential scientists in the field are also highlighted. The document aims to inform the reader about genetic engineering, related techniques, and its progression over time.
i have included terminology, types, methods, process, applications of trangenic technology.
all the pics are collected from different websites and some text books shown in reference. pictures and matter copyrights doesn't belong to me.
This lecture introduces concepts of bacterial genetics and virulence. It defines key genetic terms and describes how bacteria differ from eukaryotes in their genetics. Mobile genetic elements often facilitate the acquisition of virulence genes via horizontal gene transfer. Virulence factors do not always benefit the bacterium directly but may aid bacteriophages. Genetic methods like signature-tagged mutagenesis and Tn-seq can identify genes required for virulence in model infections.
1) The document provides an overview of DNA structure and function. It describes DNA as the genetic material that carries hereditary information from one generation to the next in the form of genes.
2) The key experiments that proved DNA is the genetic material are described, including Griffith's transformation experiment, Avery's work showing the transforming principle is DNA, and Hershey and Chase's experiment using radioactive labeling of DNA and proteins in bacteriophages.
3) Watson and Crick are credited with discovering the double helix structure of DNA in 1953 based on Chargaff's rules of base pairing and X-ray crystallography data. Their model explained DNA's ability to self-replicate semiconserv
The document provides an overview of DNA structure and function. It discusses early experiments that established DNA as the genetic material, including Griffith's experiments showing transformation in bacteria and Avery, Macleod and McCarty's experiments proving that DNA is the transforming principle. It describes Chargaff's rules, Watson and Crick's proposal of the double helix model based on X-ray diffraction data, and semiconservative DNA replication demonstrated by Meselson and Stahl's experiment using nitrogen isotopes.
Discovery of dna as the universal genetic materialRupal Agrawal
Gregor Mendel discovered genes in 1866. Friedrich Miescher isolated DNA in 1868. In the 1940s, Avery, MacLeod and McCarty conducted experiments showing that DNA is the genetic material. They found that only DNA from one type of pneumonia bacteria could transform another type of the bacteria. Similarly, Hershey and Chase showed in 1952 that when viruses infect bacteria, only the viral DNA, not proteins, enters the host cell, proving DNA is the genetic material in viruses too. These experiments established DNA as the universal genetic material.
1) Griffith discovered a "transforming principle" that allowed non-virulent bacteria to become virulent after exposure to heat-killed virulent bacteria.
2) Avery, MacLeod, and McCarty determined that the transforming principle was DNA through experiments treating components with DNAses, RNAses, and proteases.
3) Hershey and Chase provided definitive evidence that DNA is the genetic material through experiments using bacteriophages containing radioactive DNA or protein to infect bacteria, showing that only DNA was transferred.
Hershey and chase experiment-the blender experimentbiOlOgyBINGE
It was performed by Alfred Hershey and Martha Chase in 1952.
It led to confirmation of the genetic nature of DNA came from an experiment with E.coli phage T2.
for more details visit our youtube channel.
Frederick Griffith discovered the principle of transformation through experiments with Streptococcus pneumoniae bacteria. He found that heat-killed virulent S-strain bacteria could make non-virulent R-strain bacteria transform and become virulent. Later, Oswald Avery, Colin MacLeod and Maclyn McCarty discovered that DNA alone from S bacteria could transform R bacteria. Alfred Hershey and Martha Chase provided conclusive evidence that DNA, not protein, is the genetic material through experiments using bacteriophages infecting E. coli bacteria. They found that radioactive DNA, but not protein, passed from the bacteriophages into the bacterial cells.
Frederick Griffith discovered in 1928 that heat-killed bacteria contained a transforming factor that could change harmless bacteria into disease-causing bacteria. Oswald Avery and colleagues in 1944 determined that this transforming factor was DNA. Rosalind Franklin's x-ray crystallography work in 1952 provided evidence that DNA has a helical structure, which James Watson and Francis Crick used to propose their double helix model of DNA structure in 1953.
Transduction is a mode of genetic transfer between bacteria mediated by bacteriophages. During viral replication, fragments of bacterial DNA can become packaged within viral particles. These particles may then infect other bacteria and insert the donor DNA into the recipient genome. There are two types of transduction - generalized, where any bacterial DNA fragment can be transferred, and specialized, where only DNA near the site of viral integration is transferred. Cotransduction frequencies can also be used to map the relative locations of bacterial genes, as genes closer together are more likely to be cotransferred within the same viral particle. Transduction is useful for genetic engineering and mapping bacterial chromosomes.
The document summarizes the history of discoveries leading to the understanding that DNA is the molecule of heredity. It describes early experiments in the 1900s and 1920s by scientists like Griffith who found that traits could be transferred between bacteria. Further work by Avery in 1944 found that DNA was responsible for this transformation. Chargaff discovered proportional relationships between DNA bases within species. Experiments in the 1950s by Hershey and Chase and the work of Franklin, Wilkins, Watson and Crick ultimately revealed DNA's double helix structure and its role in storing and transmitting genetic information from parents to offspring.
The document provides a history of molecular biology, describing how it emerged from the union of biochemistry, genetics, microbiology, and virology in the 1930s. It summarizes several major discoveries and events, including identifying DNA as the genetic material in 1944, determining the double helix structure of DNA in 1953, cracking the genetic code in the 1960s, and using new technologies like X-ray crystallography to study macromolecules. The document traces how molecular biology aims to explain life at the molecular level starting from nucleic acids and proteins.
Lectut btn-202-ppt-l1. introduction and historical background part i (1)Rishabh Jain
1. In 1972, Paul Berg constructed the first recombinant DNA molecule in vitro by combining DNA from different organisms, marking the birth of recombinant DNA technology.
2. In 1973, Stanley Cohen and Herbert Boyer developed the first successful method of gene cloning by inserting the kanamycin resistance gene into a bacterial plasmid.
3. Recombinant DNA technology allows scientists to modify the genetic makeup of organisms and has led to important discoveries such as the production of human insulin in bacteria in 1982.
Genetic Engineering and the future of EvolutiomRicha Khatiwada
Genetic engineering will allow humans to direct their own evolution for the first time in history. By arranging the four bases of DNA - A, T, G, C - genetic instructions can be changed, altering organisms. CRISPR is a new, faster, cheaper, and more precise genetic engineering tool that can edit live cells and has reduced the cost of genetic engineering by 99%. If guided with caution, genetic engineering has the potential to cure diseases like HIV and cancer, extend human lifespans by borrowing genes from immortal species, and enhance humans for space travel by engineering plants and stronger bodies. However, there are also risks like the rise of "designer babies", dictators forcing genetic changes, and the creation of super soldiers
Horizantal gene transfer in evolution of nematodespriyank mhatre
This is a presentation on Horizontal gene transfer(HGT) in evolution of nematodes which gives us idea about importance of HGT in evolution of nematode parasitism. Here I have covered the historical events about HGT as well.
This is my First seminar in Div of Nematology.
This document discusses evidence that DNA is the genetic material that is passed from parents to offspring. It describes three key experiments:
1. Frederick Griffith's 1928 experiment on bacteria transformation showed that heat-killed bacteria could transfer genetic material to live bacteria.
2. Avery, Macleod, and McCarty's 1944 experiment purified the transforming material from Griffith's experiment and found that removal of proteins did not affect transformation, but DNA digestion did, proving DNA was the genetic material.
3. Hershey and Chase's 1952 experiment on bacteriophages, using radioactive labeling, showed that only DNA entered bacteria cells during infection, while proteins remained outside, proving DNA was the genetic material of phages.
This document discusses the Central Dogma of Biology and the discovery of DNA as the genetic material. It summarizes that:
1) Early experiments showed that chromosomes behaved like Mendel's hereditary factors and were linked to specific traits. The Hershey-Chase experiment provided definitive evidence that DNA, not protein, was the genetic material.
2) Watson and Crick discovered the double helix structure of DNA in 1953, explaining Chargaff's rules of base pairing. Semiconservative replication of DNA was demonstrated by Meselson and Stahl in 1957.
3) DNA replication requires several enzymes including DNA polymerase, helicase, ligase and primase to unwind and copy the DNA, adding
The document provides an overview of genetic engineering and its history. It discusses the basics of genetic engineering, which involves isolating and copying genetic material of interest using molecular cloning methods and inserting new DNA into the host genome. The history of genetic engineering is then explored, from early discoveries like Mendel's work with inheritance in peas to more modern developments like recombinant DNA techniques, PCR, and the creation of the first transgenic animal. A number of influential scientists in the field are also highlighted. The document aims to inform the reader about genetic engineering, related techniques, and its progression over time.
i have included terminology, types, methods, process, applications of trangenic technology.
all the pics are collected from different websites and some text books shown in reference. pictures and matter copyrights doesn't belong to me.
This lecture introduces concepts of bacterial genetics and virulence. It defines key genetic terms and describes how bacteria differ from eukaryotes in their genetics. Mobile genetic elements often facilitate the acquisition of virulence genes via horizontal gene transfer. Virulence factors do not always benefit the bacterium directly but may aid bacteriophages. Genetic methods like signature-tagged mutagenesis and Tn-seq can identify genes required for virulence in model infections.
1) The document provides an overview of DNA structure and function. It describes DNA as the genetic material that carries hereditary information from one generation to the next in the form of genes.
2) The key experiments that proved DNA is the genetic material are described, including Griffith's transformation experiment, Avery's work showing the transforming principle is DNA, and Hershey and Chase's experiment using radioactive labeling of DNA and proteins in bacteriophages.
3) Watson and Crick are credited with discovering the double helix structure of DNA in 1953 based on Chargaff's rules of base pairing and X-ray crystallography data. Their model explained DNA's ability to self-replicate semiconserv
The document provides an overview of DNA structure and function. It discusses early experiments that established DNA as the genetic material, including Griffith's experiments showing transformation in bacteria and Avery, Macleod and McCarty's experiments proving that DNA is the transforming principle. It describes Chargaff's rules, Watson and Crick's proposal of the double helix model based on X-ray diffraction data, and semiconservative DNA replication demonstrated by Meselson and Stahl's experiment using nitrogen isotopes.
1. In the early 1950s, scientists including Rosalind Franklin, Maurice Wilkins, James Watson, and Francis Crick were working to determine the structure of DNA. Franklin's X-ray crystallography photos provided key evidence of a double helix structure.
2. In 1953, Watson and Crick published a paper proposing that DNA consists of two intertwined strands coiled around each other in the shape of a double helix, with bases on the inside pairing according to Chargaff's rules. This successfully described DNA's structure and how it can replicate.
3. Their model built upon prior discoveries including Griffith's transformation experiments, Avery's finding that DNA is the genetic material, Chargaff
The document summarizes key evidence and discoveries that led to the acceptance of DNA as the genetic material:
1) Chargaff's rule showed equal amounts of certain DNA base pairs and hinted at DNA's structure.
2) Franklin and Wilkins' X-ray crystallography provided clues to Watson and Crick, whose 1953 double helix model explained DNA's structure.
3) Griffith's experiment showed one type of bacteria could transform another through some "transforming principle," later shown by Avery, MacLeod and McCarty to be DNA. Hershey and Chase's experiment confirmed DNA is the genetic material of viruses.
Frederick Griffith conducted an experiment in 1928 demonstrating that genetic information could be transferred between bacteria strains. He found that mice survived when injected with a non-virulent strain or heat-killed virulent strain, but died when injected with a mixture of both. This showed that the non-virulent strain acquired some "transforming principle" making it virulent. Later experiments by Avery, MacLeod and McCarty purified components from the bacteria and found that only DNA was responsible for the transformation, identifying DNA as the genetic material.
This document provides an overview of DNA and genetics. It discusses how DNA was established as the genetic material through experiments in the 1900s and 1950s. It describes the structure of DNA as a double helix based on the work of Watson, Crick, Wilkins and Franklin. It also summarizes Mendel's laws of inheritance and how chromosomes package and transmit genetic information from one generation to the next. The document traces the history of genetics from early Greek philosophers through modern discoveries that have revolutionized our understanding of heredity and molecular biology.
1. Frederick Griffith discovered in 1928 that a "rough" non-pathogenic strain of pneumonia bacteria could be transformed into a "smooth" pathogenic strain through exposure to heat-killed pathogenic bacteria.
2. Hershey and Chase provided evidence in 1952 that DNA, not protein, was the genetic material through experiments using radioactive labeling of bacteriophages.
3. Watson and Crick deduced the double-helix structure of DNA in 1953 based on Chargaff's rules of DNA composition and Rosalind Franklin's X-ray crystallography photos of DNA.
Basic concepts & scope of recombinant DNA technologyRavi Kant Agrawal
Recombinant DNA technology involves combining DNA molecules from different sources and introducing them into host cells. Key developments include the discovery that DNA carries genetic information (Avery, 1944), determining DNA's structure (Watson and Crick, 1953), developing techniques to cut and join DNA (restriction enzymes and ligase, 1970s), and creating the first recombinant DNA molecules by combining bacterial plasmid and phage DNA (Cohen and Boyer, 1973). These advances laid the foundation for genetic engineering.
The document summarizes the central dogma of biology and the discovery of DNA as the genetic material. It describes key experiments that showed DNA replicates in a semiconservative manner, with each parental strand serving as a template for a new complementary daughter strand. The process of DNA replication requires several enzymes including DNA polymerase, helicase, ligase and primase to unwind, copy and join new DNA strands.
1) Bacterial transformation experiments by Griffith and Avery's team showed that DNA is the genetic material that can be transferred between bacteria to alter traits like disease-causing ability.
2) Hershey and Chase's experiments with bacteriophages demonstrated that viral DNA, not the protein coat, enters bacterial cells to transmit the viral genes.
3) DNA functions to store, copy, and transmit genetic information from parent to daughter cells and between generations through its molecular structure and role in heredity.
research done to prove DNA a genetic materialPartha Sarathi
1. Genetic inheritance refers to the transmission of traits from parents to offspring through genetic material. DNA was identified as the genetic material based on its ability to stably replicate and mutate over generations.
2. Experiments in the early 20th century identified DNA as the substance within chromosomes that determines inheritance. Key experiments included Avery, MacLeod and McCarty demonstrating transformation is caused by DNA.
3. The structure of DNA was elucidated in 1953 when Watson and Crick proposed the double helix model based on X-ray crystallography data from Franklin and Chargaff's rules regarding nucleotide base ratios. This established DNA as the molecule of heredity.
The document summarizes several key experiments that helped establish DNA as the genetic material:
1) Griffith's transforming principle experiment in 1928 demonstrated that something from heat-killed bacteria could transform live bacteria, indicating the presence of a "transforming principle."
2) Avery, McCarty, and MacLeod purified this principle in 1944 and showed that it was DNA through a series of tests.
3) Hershey and Chase's 1952 experiment using bacteriophage proved that the genetic material injected into bacteria was DNA, not protein.
4) Chargaff formulated his rules in 1950 showing equal concentrations of DNA bases adenine and thymine and guanine and cytosine.
5) Mesel
DNA is made of two linked strands that wind around each other to resemble a twisted ladder — a shape known as a double helix. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T).
Fredrick Griffith discovered that heat-killed pneumonia bacteria could transform harmless bacteria into deadly disease-causing bacteria when mixed together and injected into mice. This led researchers like Oswald Avery to determine that DNA was the molecule responsible for transformation. Further experiments by Hershey and Chase showed that the genetic material of viruses that infect bacteria is DNA. Together, these findings established DNA as the genetic material that gets passed from parents to offspring and controls inheritance.
The document discusses the hierarchy of knowledge in biochemistry, molecular biology, and biotechnology. It begins by explaining how biochemistry initially focused on proteins and enzymes, while molecular biology focused on nucleic acids and the structure and function of genes. Biotechnology emerged due to advances in molecular biology and recombinant DNA techniques. The key areas of each discipline are defined, including how molecular biology studies how organisms are made from simple molecules at the cellular level.
DNA replication is semiconservative and bidirectional. It involves unwinding the parental DNA strands at an origin of replication followed by synthesis of new complementary strands. Each parental strand serves as a template for a new daughter strand. DNA polymerase adds nucleotides to the 3' end of the growing strand based on complementary base pairing. The leading strand is synthesized continuously while the lagging strand is synthesized discontinuously in short segments called Okazaki fragments. RNA primers are required for initiation and DNA polymerase proofreads and corrects errors to ensure high fidelity. Telomeres and the telomerase enzyme allow complete replication of linear chromosomes.
Historical development of genetics finalHotaru Imai
This document summarizes the historical development of genetics from early concepts to modern understanding. It describes key figures and their contributions, including:
- Mendel who established basic laws of inheritance through pea plant experiments.
- Watson and Crick who discovered the double helix structure of DNA.
- Chargaff who found regular proportions of DNA bases between species.
- Nirenberg who helped discover the genetic code.
- Berg who created the first recombinant DNA molecules.
The document traces the progression of genetics from early theories to establishing DNA as the molecule of inheritance and cracking the genetic code.
Introduction to Genetic Material, Physical and Chemical properties of the same and various types of coiling mechanisms as well as information about chromosomal and extra-chromosomal DNA.
MOLECULAR BASIS OF INHERITANCE -DNA AS GENETIC MATERIAL
Dna an overview
1. DNA – An overview
Dr. Siva Ramamoorthy
School of Biosciences and Technology
VIT University
India
email: rsiva77in@rediffmail.com
2. WHAT IS GENE?
2005
2003
DNA Double Helix,
Watson & Crick
Human genome
Nature, 1953 Project
Inactivation of different X genes
3. • The physical and functional unit of heredity
that carries information from one generation
to the next
• DNA sequence necessary for the synthesis
of a functional protein or RNA molecule.
4.
5. GENE
• Gene were first detected and analyzed by Mendel and
subsequently by many other scientist (Mendel stated that
physical traits are inherited as “particles”)
Mendel did not know that the “particles” were actually
Chromosomes & DNA
• Subsequent studies shows the correlation between transmission
of genes from one generation to generation (Segregation and
independent assortment) and the behavior of chromosomes
during sexual reproduction, specifically the reduction division
of meiosis and fertilization.
• These and related expt. provided a strong early evidence that
genes are usually located on chromosomes.
6. What are the requirements to fulfill as a genetic
material?
• 1. The genotype function or replication:
• The genetic material must be capable of storing genetic
information and transmitting this information faithfully
from parents to progeny, generation after generation.
• 2. The phenotype function or gene expression
• The genetic material must control the development of
phenotype of the organism, be it a virus, a bacterium, a
plant or animal.
• That is, the genetic material must dictate the growth and
differentiation of the organism from single celled zygote to
the mature adult.
7. • Chromosomes are composed of two types of large organic
molecules (macromolecules) called proteins and nucleic acids.
• The NA are of two types: DNA and RNA
• For many years there was considerable disagreement among
scientists as to which of these macromolecules carries genetic
information.
• During the 1940s and early 1950s, several elegant experiments
were carried out that clearly shows that NA is genetic material
rather than protein.
• More specifically these expt. shows that DNA is genetic material
for all living organism except for RNA viruses.
8. DNA , The Genetic material
• The first direct evidence showing that the genetic
material is DNA rather than RNA or protein was
published by O.T. Avery, Macleod and C.M.
Mccarty in 1944.
• They demonstrated that the component of the cell
responsible for the phenomenon of transformation
in the bacterium Diplococcus pneumoniae is
DNA.
9. Griffith experiment
• The phenomenon of transformation was first discovered by
Frederick Griffith in 1928.
• Pneumococci, like all other living organisms, exhibit genetic
variability that can be exhibit with different phenotype
• The two phenotypic characteristic of importance in Griffith
experiment were:
• 1. presence or absence of a surrounding polysaccharide
capsule, and
• 2. the type of capsule, that is, the specific molecular
composition of the polysaccharide present in the capsules.
10. • When grown in appropriate media in petri
dishes, pneumococci with capsule form
large, smooth colonies and thus designated
as Type S.
• Such encapsulated pneumococci are quite
pathogenic to mammals, so they are
Smooth
virulent
• The other type is nonpathogenic
(nonvirulent) has no polysaccharide
capsule.
• Such a non-encapsulated, nonvirulent
pneumococci form small, rough-surfaced
colonies when grown on medium and are Rough
thus designated as Type R.
11. Colony morphology Reaction with Antiserum
prepared against
Type Appearance Size Capsule Virulence Type IIS Type IIIS
IIR Rough Small Absent Non-virulent none none
IIS Smooth Large Present Virulent Agglutination none
IIIR Rough Small Absent Non-virulent none none
IIIS Smooth Large Present Virulent none
Agglutina
12.
13. • Griffith unexpected discovery was that if he injected heat-
killed Type IIIS pneumococci (Virulent when alive) plus
live Type IIR pneumococci (nonvirulent) into mice, many
of the mice died.
• But when mice were injected with heat-killed Type IIIS
pneumococci alone none of the mice died.
• Thus, the “transformation” of nonvirulent Type IIR cells to
virulent Type IIIS cells cannot be explained by mutation,
rather some component of dead Type IIIS cells (the
“transforming principle”) must convert living Type IIR to
Type IIIS.
• Subsequent expt. Showed the phenomenon described by
Griffith now called “transformation”.
14. Proof That the “Transforming
Principle” is DNA
In 1944, Avery, Macleod, and McCarty published the
results of extensive and laborious expt.
They confirmed through the experiments that
“transforming particle is DNA”.
In a highly purified DNA from Type IIIS cells was
treated with:
1. Deoxyribonuclease (DNase)
2. Ribonuclease (RNase)
3. Protease.
15.
16. The Hershey – Chase Experiment
• Additional direct evidence indicating that DNA is the
genetic material was published in 1952 by A.D. Hershey
(1969 Nobel Prize winner) and M.Chase.
• These experiments showed that the genetic information of a
particular bacterial virus (bacteriophage T2) was present in
DNA.
• T2 Phages infects the E.coli bacterium
17. • Bacteriophage T2 is composed of 50% protein and
about 50% DNA.
• Experiments prior to 1952 had shown that all
bacteriophage T2 reproduction takes within E.coli
cell.
• Therefore, when Hershey and Chase showed that
the DNA of the virus particle entered the cell,
where as most of the protein of the virus remained
absorbed to the outside cell.
• This is strongly implied that the genetic
information necessary for viral reproduction was
present in DNA.
18. • The basis of the Hershey –Chase experiment is that
DNA contains Phosphorous but no sulfur, where as
Proteins contain sulfur but not phosphorous.
• Thus, they were able to specifically label either
(1) the phage DNA by growth in a medium containing
the radioactive isotope of Phosphorous, P32 , in the place
of normal isotope P31
• Or (2) the phage protein coats by growth in a medium
containing radioactive sulfur S35, in the place of normal
S32
19. • T2 phages labeled with S35 were mixed with E.coli
cells for few minutes.
• It was then subjected to shearing forces by placing
infected cells in a Waring blender
• It was found that most of the radioactivity could
be removed from the cells without affecting
progeny production.
• When T2 phages labeled with P32, radioactivity was
found inside the cells, that is, it was not subject to
removal by shearing in a blender.
21. What was their conclusion regarding the source
of genetic material in phages?
22. RNA as genetic material in small viruses
• H.Fraenkel- Conrat and B.Singer in 1957 conduct experiment on TMV.
• By using the appropriate chemical treatment one can separate the protein
coats of TMV from the RNA.
• Moreover, this process is reversible; by mixing the proteins and the RNA
under appropriate conditions, “reconstitution” will occur.
• They took two different strains of TMV, separated the RNAs from the
protein coat.
• Reconstituted “mixed” viruses by mixing the proteins of one strain with
the RNA of the second strain, and vice versa.
• When these mixed viruses were infected with tobacco leaves, the progeny
was phenotypically and genotypically identical like parent from where
RNA had been obtained.
23.
24. DNA STRUCTURE
Nucleic acids first called “nuclein” because they were
isolated from cell nuclei by F. Miescher in 1869
• Each nucleotide is composed
of
(1) a Phosphate group
(2) a five – carbon sugar (or
Pentose), and
(3) a cyclic nitrogen containing
compound called a base.
25. In DNA, the sugar is 2-deoxyribose (thus the name
deoxyribonucleic acid)
In RNA, the sugar is ribose (thus ribonucleic acid).
26. • There are four different bases commonly found in DNA:
Adenine
Guanine
Thymine and
Cytosine.
• RNA also contains adenine, guanine and cytosine, but has
different base, uracil in the place of thymine.
27. Adenine and Guanine are double ring base called Purines
6-aminopurine 2-amino-6-oxypurine
Cytosine, thymine, and uracil are single-ring base called Pyrimidines.
4-amino-2-
oxypyrimidine 2,4-oxypyrimidine 2,4-oxy-5-pyrimidine
28. The Watson and Crick DNA Double helix
• The correct structure of DNA was first
deduced by J.D. Watson and F.H.C.Crick in
1953.
• Their double helix model of DNA structure
was based on two major kind of evidence.
1. Chargaff’s rule
2. X – ray diffraction patterns.
29. Chargaff’s rule
• The composition of DNA from many different organisms was
analyzed by E.Chargaff and his colleagues.
• It was observed that concentration of thymine was always equal to
the concentration of adenine (A = T)
• And the concentration of cytosine was equal to the concentration
of guanine (G = C).
• This strongly suggest that thymine and adenine as well as cytosine
and guanine were present in DNA with fixed interrelationship.
• Also the total concentration of purines (A +G) always equal to the
total concentration of pyrimidine (T +C). However, the (T+ A)/
(G+C) ratio was found to vary widely in DNAs of different
species.
30.
31. X ray diffraction
• When X rays are focused through isolated macromolecules or
crystals of purified molecules, the X ray are deflected by the atom of
the molecules in specific patterns called diffraction patterns.
• It provides the information about the organization of the components
of the molecules.
• Watson and Crick had X ray crystallographic data on DNA structure
from the studies of Wilkins and Franklin and their coworkers.
• These data indicated that DNA was a highly ordered, multiple
stranded structure with repeating sub structures spaced every 3.4 Ao
(1 Angstrom = 10-10 m )
32. X-ray diffraction patterns of DNA
– Rosalind Franklin and Maurice Wilkins
The central cross shaped pattern as indicative of a helical structure.
The heavy dark patterns (top and bottom) indicate that the bases
are stacked perpendicular to the axis of the molecule.
33. Double Helix
• Watson and Crick proposed that DNA exists as a double helix in
which two polynucleotide chains are coiled above one another in
a spiral.
• Each polynucleotide chain consists of a sequence of nucleotide
linked together by Phosphodiester bonds.
• The two polynucleotide strands are held together in their helical
configurations by hydrogen bonding.
• The base pairing is specific
• That is, adenine is always paired with thymine and guanine is
always paired with cytosine
• Thus, all base-pairs consists of one purine and one pyrimidine.
• Once the sequence of bases in one strand of DNA double helix is
known, it is possible to know the other strand sequence of base
because of specific base pairing.
34.
35. • In their most structural configuration,
adenine and thymine form two hydrogen
bonds, where as guanine and cytosine
form three hydrogen bonds.
• The two strands of a DNA are
complementary (not identical) to each
other. It is this property, that makes
DNA uniquely suited to store and
transmitting the genetic information.
• The base-pairs in DNA are stacked 34Ao
apart with 10 base-pairs per turn (3600)
of the double helix
• The sugar – phosphate backbones of the
two complementary strands are
antiparallel, that is they have opposite
chemical polority.
36. • As one move unidirectionally along a
DNA double helix, the phosophodiester
bonds in one bonds in one strand go from a
3’Carbon of one nucleotide to a 5’Carbon
of the adjacent nucleotide.
• Where as those in complementary strand
go from 5’Carbon to a 3’carbon.
• This opposite polarity of the
complementary strands is very important
in considering the mechanism of
replication of DNA.
• The high degree of stability of DNA
double helices results in part from the large
number of hydrogen bonds between base
pairs.
37. • Although each hydrogen bond by itself quite
weak, since no. of hydrogen bonds are more, it
can withstand.
• The planar sides of the base pair are relatively non
polar and thus tend to be water insoluble
(hydrophobic).
• The hydrophobic core stacked base-pairs
contributes considerable stability to DNA
molecules present in the aqueous protoplasms of
living cells.
38. Conformational Flexibility of DNA Molecule
• The vast majority of the DNA molecules present in the
aqueous protoplasms of living cells almost certainly exists
in the Watson – Crick double helix from just described.
– This is the B form of DNA
• B form represent the 92% relative humidity.
• In fact, intracellular B-form DNA appears to have an
average of 10.4 nucleotide-pairs per turn, rather than 10.
39. • In high concentration of salts
or in a dehydrated state,
(75% humidity) DNA exists
in the A- form, which has 11
nucleotide-pairs per turn.
• Recently, certain DNA
sequences have been shown
to exist in a unique left
B-DNA A-DNA Z-DNA
handed, double helical form
called Z-DNA. Form Residues Pitch
Per Turn A0
• The helices of A and B form
DNA are wound in a right A 11 24.6
handed manner.
B 10 33.2
Z 12 45.6
40.
41. Did you know?
• Each cell has about 2 m of
DNA.
• The average human has 75
trillion cells.
• The average human has
enough DNA to go from
the earth to the sun more
The earth is 150 billion m
than 400 times. or 93 million miles from
• DNA has a diameter of the sun.
only 0.000000002 m.
42. Semiconservative Replication of DNA
• Living organism perpetuate their kind reproduction.
• This may simple fission as in bacteria or complex
mode of reproduction as in higher plants or animals.
• In all cases, however reproduction entails the
faithful transmission of genetic information of the
progeny.
• Since the genetic information is stored in DNA, the
replication of DNA is central to all biology
43. Semiconservative Replication of DNA
• When Watson and Crick proposed the double helical structure of
DNA with its complementary base pairing, they immediately
recognized that base pairing specificity could provide the basis for
duplication.
• If the two complementary strands of a double helix separated, (by
breaking the H2 bond) each parental strand could direct the
synthesis of a new complementary strand.
• That is each parental strand could serve as a template for a new
complementary strand.
• Adenine for e.g., in the parent strand synthesis of Thymine in
complementary strand.
• This mechanism of DNA replication is called semiconservative
replication
44. • In considering possible
mechanism of DNA replication,
three different hypothetical
modes are apparent.
• 1. Semiconservative
• 2. Conservative
• 3. Dispersive
45. Conservative: parental double
helix remain intact (is totally
conserved) and somehow
directs the synthesis of a
“progeny” double helix
composed of two newly
synthesized strand.
Dispersive: Here, parental
strand and progeny strand
become interspersed through
some kind of a
fragmentation, synthesis,
and rejoining process.
46. The Meselson – Stahl Experiment
• They proved that DNA replicates semiconservatively in
1958 by the common bacteium E.coli.
• Meselson and Stahl grew E.coli cells for many
generations in a medium in which the heavy isotope of
nitrogen N15 had been substituted for the normal, light
isotope, N14.
• The purine and pyrimidines bases in DNA contain
nitrogen.
• Thus the DNA grown on N15 will have a greater density
(Wt. per vol.) than cells grown in N14.
• Since molecules of different densities can be separated by
equilibrium density gradient centrifugation, they proved .
47. • The density of most DNAs is about same as that of
heavy salts such as CsCl.
• For e.g., the density of 6M CsCl is about 1.7g/cm3
• E.coli DNA containing N14 has density about 1.710
g/cm3
• Where as E.coli DNA containing N15 has density
about 1.724 g/cm3
• When a heavy salt solution such as 6M CsCl
centrifuged at very high speed (30,000-50,000 rpm)
for 48-72 hrs, an equilibrium density gradient is
formed.
48. • Meselson and Stahl took cells that had been growing in
medium containing N15 for several generation (thus
contained “heavy” DNA).
• They transferred them to medium containing N14.
• After allowing cells to grow in the presence of N14 for
varying periods of time, the DNA was extracted and
analyzed in CsCl equilibrium density gradient.
• The results of their expt. are only consistent with
semiconservative model.
49. • All the DNA isolated from cells after one
generation of growth in medium containing N14
had a density halfway between the densities of
‘heavy’ and ‘light’ DNA.
• This intermediate referred to as ‘hybrid’
• After 2 generations of growth in medium
containing N14 , half of the DNA was of “hybrid”
and half was “light”
• This prove Semiconservative
53. Cairn’s Experiment
• The visualization of replicating chromosome was first
accomplished by J. Cairns in 1963 using the technique called
autoradiography.
• Autoradiography is a method of detecting and localizing
radioactive isotopes in macromolecules by exposure to
photographic emulsion that is sensitive to low energy radiation.
• Autoradiography is particularly useful in studying DNA
metabolism because DNA can be specifically labeled by growing
cells on [H3]thymidine, the tritiated deoxyribonucleoside of
thymidine.
• Thymidine is incorporated exclusively into DNA; it is not present
in any other major component of the cell.
54. • Cairns grew E.coli cells in medium containing [H3]thymidine for
varying period of time.
• He lysed the cell very gently so as not to break the chromosomes
and he carefully collected the chromsomes on membrane filter.
• These filters are affixed to glass slides, coated with emulsion
sensitive to β – particles (the low energy electrons emitted
during decay of tritium) and store in dark for radioactive decays.
• The autoradiograph observed when the films were developed.
• It showed that the chromosomes of E.coli are circular
structures that exist as θ shaped intermediates during
replication.
55. John Cairns
Bacterial
culture
*T *T
*T *T
Grow cells for several generations *T
in media with low Small amounts of 3 H thymidine
*T *T
concentration of are incorporated into new DNA
3
H- thymidine All DNA is lightly
labeled with radioactivity
Add a high
concentration
Grow for of 3 H- thymidine
brief period
*T *T
*T *T
*T
*T *T
*T
*T
*T
*T
*T
*T of time
*T *T
*T *T *T
*T
*T *T *T *T *T *T *T *T
Dense label at the replication fork
where new DNA is being made
Cairns then isolated the chromosomes by lysing the cells very very
gently and placed them on an electron micrograph (EM) grid which
he exposed to X-ray film for two months.
56. • These autoradiograph further indicated that the unwinding of the
complementary strands and their semiconservative replication
occurs simultaneously or closely coupled.
• Cairns interpretation of the autoradiographs was the
semiconservative replication started at a site on the chromosome,
which he called the, “origin” and proceeded unidirectionally
around circular structure.
• Subsequent evidence has shown his interpretation is incorrect on
one point: replication actually proceeds bidirectionally , not
unidirectionally.
57. Unique origin and Bidirectional replication
• Cairn’s result provided no information as to whether the origin
(the site at which replication is initiated) of replication is unique
or occurs at random on the chromosome.
• Moreover his results did not allow him to differentiate between
uni - and bidirectional replication.
• We now have direct evidence showing that replication in E.coli
and several other organisms proceeds bidirectionally from a
unique origin.
• These features of DNA replication can be illustrated most simply
and convincingly by experiments with some of the small bacterial
virus.
58. Unique origin and Bidirectional replication
• Bacteriophage lambda is like T2 a virus that grows in E.coli.
• It has a small chromosome consisting of a single linear molecule
of DNA only 17.5 µm long.
• The phage λ chromosome has 12 nucleotides long at 5’end of
each complementary strand.
• These single stranded ends called, “cohesive” or “sticky” ends,
are complementary to each other.
3’ 5’
G
GGGCGGCGACCTC
5’ 3’
60. • The cohesive ends of a λ chromosome can thus base-pair to
form a hydrogen bonded circular structure.
• This conversion from the H2 bonded circular form to the
covalently closed circular form is catalyzed by
polynucleotide ligase, a very important enzyme that seals ss
breaks in DNA double helices.
• λ chromosome when replicates to circular form via θ -
shaped intermediates.
• Bidirectional replication was shows different at different
segments like the region rich in AT and CG.
• Schnos and Inman conducted an experiment on it using a
technique called “denaturation mapping”.
61. • When the DNA molecules are exposed to 1000 C or high pH
(11.4), the hydrogen and hydrophobic bonds that hold the
complementary strands are broken and two strands are
separate.
• This process is called denaturation.
• Since, A-T region contains only 2 Hydrogen bonds it denature
more easily than C-G
• It denature to form “denaturation bubbles” which are
detectable by electron microscopy, while C-G remain in the
duplex state.
• These denaturation bubbles uses as a physical markers
whether the lambda chromosome is in its mature linear form
or circular form or its θ -shaped intermediate .
62.
63. The origin of replication is
located at 14.3 µm from the left
end of the chromosome.
Four chromosomes are shown
at different stage of replication
64. The Replication of DNA
• The in vitro synthesis of DNA was first accomplished
by Arthur Kornberg and his coworkers in 1957.
• Kornberg received the Nobel prize in 1959 for this
work.
• He isolated an enzyme from E.coli that catalyzes the
covalent addition of nucleotides to preexisting DNA
chains.
• Initially this enzyme is called DNA Polymerase or
Kornberg enzyme, now known as DNA Polymerase I.
65. DNA POLYMERASES
• After Kornberg’s discovery and extensive work with DNA
polymerase I of E.coli, a large number of DNA polymerases
have been isolated.
• Three different Polymerases (I,II, and III) have been identified
and studied in E.coli and B.subtilis.
• The precise functions of some of the polymerases are still not
clear.
• Early it was believed that Polymerase I was considered as the
major replicative enzyme.
• But while study with the mutant Pol A ( where the Polymerase
enzyme cannot synthesis) shows, replication same as that of
Normal rates.
66. • However these mutants are defective in their capacity to repair
damage to DNA (e.g., caused from UV radiation)
• This and other evidence suggest that major function of
polymerase I is DNA repair.
• Still other evidence indicates that DNA polymerase I
responsible for the excision (removal) of RNA primers used in
the initiation of DNA synthesis.
• DNA Polymerase II function is uncertain, but it expect involve
in DNA repair in the absence of DNA Polymerase I and III.
• DNA Polymerase III, plays an essential role in DNA
replication, because mutant growing under conditions where no
functional polymerase III is synthesized, DNA synthesis stops.
67. • Most of the prokaryotic DNA polymerases studied so far not
only exhibit 5’ to 3’ polymerase activity , but also 3’ to 5’
exonuclease activity.
• An exonuclease is an enzyme that degrades nucleic acid.
• Both activities are present in the same macromolecule.
• The 3’ to 5’exonuclease activity catalyzes the removal of
nucleotides, one by one, from 3’ends of polynucleotide chains.
• Some polymerases, such as DNA polymerase I of E.coli also
have 5’ to 3’ exonuclease activity.
• In fact, the 3’ to 5’ exonuclease activity of DNA polymerases
carries out a critical “Proof reading” or “editing” function that is
necessary for DNA replication.
68. • When an unpaired or incorrectly paired base are
clip off by exonucleases.
• When an appropriate base-paired terminus results,
polymerase begins resynthesis by adding
nucleotides to the 3’ end.
• The 5’ to 3’ exonuclease activity of many
prokaryotic DNA polymerases is also very
important.
• It functions in the removal of segments of DNA
damaged by UV and other agents.
69. • Analogous to RNA, DNA is synthesized from
deoxynucleoside 5-triphosphate precursors (dNTPs).
• The enzyme requires the 5’triphosphates of each of
the four deoxyribonucleosides:
• dATP : deoxyadenosine triphosphate
dTTP: deoxythymidine triphosphate (TTP)
dGTP: deoxyguanosine triphosphate
dCTP: deoxycytidine triphosphate
70. This enzyme is active only in the presence of Mg+ ions and
preexisting DNA.
This DNA must provide two essential components, one serving a
primer function and other a template function.
1. Primer DNA: DNA polymerase I cannot initiate the synthesis of
de novo. It has an absolute requirement for a free 3’hydroxyl on
preexisting DNA chain.
DNA Polymerase I catalyzes the formation of a phosphodiester
bridge between the 3’OH at the end of the primer DNA chain and
5’phosphate of the incoming deoxyribonucelotide.
The direction of synthesis is always 5’ to 3’
2. Template provides ssDNA that will direct the addition of each
complementary deoxynuceotide
71. “Replicating Apparatus” is complex
• DNA replication is complex.
• It is carried out by multienzyme complex, often
called, replication apparatus or the replisome.
• In eukaryotes, the components of replication
machinery are just beginning to be identified.
• Even in prokaryotes, DNA replication requires
many different proteins
72. • Replication fork: The junction between the newly separated
strands and unreplicated double stranded DNA
• Leading and Lagging strand: Due to the anti-parallel nature of
DNA, one strand will synthesis continuously towards replication
fork and other strand will synthesis discontinuously away from the
replication fork.
• The continuously synthesizing strand is called leading strand and
discontinuously synthesizing strand is called lagging strand.
• Okazaki fragment: A short fragment of DNA formed on the
lagging strand during replication is called Okazagi fragment. It will
be around 100 – 1000 bp in length. In eukaryotes it identified about
100-200 nucleotides length.
• Processivity: The ability of an enzyme to catalyze many reactions
before releasing its substrate is called processsivity
73. • To prepare DNA for replication, many proteins are involved
in replication
• These proteins are required because DNA must be single-
stranded before replication can proceed.
• The following are important Protein and enzyme required for
DNA replication:
1. DNA helicases
2. Single stranded DNA binding proteins (SSB)
3. Topoisomerases / DNA gyrase
4.Primase
5. DNA Polymerases 6. Sliding DNA clamps
7. RNAse H 8. DNA ligase
74. • DNA Helicases - These proteins bind to the double
stranded DNA and stimulate the separation of the two
strands.
• DNA single-stranded binding proteins - These
proteins bind to the ssDNA as a tetramer and stabilize
the single-stranded structure that is generated by the
action of the helicases.
• Their binding exhibits cooperativity (the binding of
one tetramer stimulates the biding of additional
tetramers)
• Replication is 100 times faster when these proteins
are attached to the single-stranded DNA.
75. • DNA Gyrase - This enzyme catalyzes the formation of
negative supercoils that is thought to aid with the unwinding
process.
• It catalyzes the removal of Positively supercoils in DNA,
which considered to be essential for replication and are
believed to play a key role in unwinding process .
• Primase – DNA replication require RNA primers to begin.
• Primase is a specialized RNA polymerase which make short
RNA primers using ssDNA as a template
• Primase activity requires the formation of complex of primase
and at least six other proteins.
• This complex is called Primosome
76. • DNA Polymerase: The synthesis of DNA is catalyzed by
DNA Polymerase.
• It can add only dNTPs to the 3’ and form polynucleotide.
• Sliding DNA Clamps: It is to increase the degree of
processivity of the DNA Polymerase sliding DNA clamps
surrounds the DNA and binds to the DNA polymerase and
holding them together.
• RNAse H: To complete the DNA replication, RNA primers
must be removed.
• RNAse H Specifically degrade RNA that base paired with
DNA. (H stands for Hybrid as RNA – DNA Hybrid)
77. • DNA Ligase - Nicks occur in the
developing molecule because the RNA
primer is removed and synthesis proceeds in
a discontinuous manner on the lagging
strand.
78.
79. This powerpoint was kindly donated to
www.worldofteaching.com
http://www.worldofteaching.com
Is home to well over a thousand powerpoints
submitted by teachers. This a free site. Please visit
and I hope it will help in your teaching