This document provides an overview of gene expression from DNA to protein. It discusses how genes code for proteins, the process of transcription of DNA to mRNA, and translation of mRNA to amino acid sequences to form proteins. Key points covered include:
- Genes contain the code for proteins and a change in the gene results in a change to the protein's amino acid sequence.
- Transcription involves copying a gene's DNA sequence into a complementary mRNA sequence. Translation then converts the mRNA sequence into the amino acid sequence of a protein.
- The genetic code specifies which three-letter codon in mRNA corresponds to each amino acid. Translation uses this code to build proteins from mRNA instructions.
Recombination
Breaking and rejoining of two parental DNA molecules to produce new DNA molecules
Types of recombination
Definition of recombination
Gene Conversion – Characteristics
Holliday model
Holliday junction cleavage
Recombination
Breaking and rejoining of two parental DNA molecules to produce new DNA molecules
Types of recombination
Definition of recombination
Gene Conversion – Characteristics
Holliday model
Holliday junction cleavage
Introduction
Defination
Nitrogenous Bases
Components of nucleotide
Structure of nucleotide
Synthesis of nucleotide
Function
Length unit
Importance of nucleotide sequence
Biological significanc
Recent research
Conclusion
References
chloroplast being the second semi-autonomous organelle of the plant cell also harbours its genome. the presentation includes various characteristic features of this organelle genome along with its functional pecularities and significance
a two page pdf showing the role of organisms who had rna as their genetic materials and how it lead to the evolution of organisms. by Dr. Tithi Parija (asst professor) from KIIT school of biotechnology
Introduction
Defination
Nitrogenous Bases
Components of nucleotide
Structure of nucleotide
Synthesis of nucleotide
Function
Length unit
Importance of nucleotide sequence
Biological significanc
Recent research
Conclusion
References
chloroplast being the second semi-autonomous organelle of the plant cell also harbours its genome. the presentation includes various characteristic features of this organelle genome along with its functional pecularities and significance
a two page pdf showing the role of organisms who had rna as their genetic materials and how it lead to the evolution of organisms. by Dr. Tithi Parija (asst professor) from KIIT school of biotechnology
Brief Concepts and Questions EXAM 2 Chapter 8 DNA RNA Protein What i.pdfmckenziecast21211
Brief Concepts and Questions EXAM 2 Chapter 8: DNA RNA Protein What is DNA? a
phosphate Structure of DNA: Building blocks are called nucleotides Each nucleotide is
composed of three br uithofenas bee. What makes DNA so special? Provide 4 reasons, below
DNA DNA (Replication): Where does DNA replication take place? When does DNA replication
take place? Explain steps involved in DNA replication: DNA RNA Protein (Gene Expression)
Involves 2 processes: 1. Transcription 2. Translation Explain the Synthesis of Proteins (Gene
Expression): o DNA RNA Protein What is RNA? What is \"codon What is \"anticodon\" What is
a protein molecule? DNA mutation; Change in nucleotide bases of DNA Duplex Point mutation
Frame shift mutation
Solution
Question
Answer
Where does DNA replication take place:
It takes place in the nucleus in case of eukaryotic cells and in the cytoplasm in case of
prokaryotic cells
When does DNA replication take place:
DNA replication occurs during the S-phase during cell cycle, so that cell can make an extra copy
of genetic material.
Explain steps involved in DNA replication:
Initiation: During initiation, the proteins will bind to the origin of replication; helicase unwinds
the DNA helix which results in the formation of two replication forks.
Elongation: A RNA primer sequence will be added to this the DNA pol III will add the
nucleotides in 5’ to 3’ direction and chain will elongate.
Termination: In case of bacteria, termination of replication occurs whenever two replication
forks meet each other from the opposite end of the parental chromosome.
Transcription
Gene expression first step is transcription, here a particular segment of DNA will be copied into
RNA with the help of the enzyme RNA polymerase
Translation
Translation is the final step of the gene expression. Here mRNA will be used to synthesize the
polypeptide chain. The information present in the mRNA in the form of codon will code for the
amino acids needed for polypeptide chain synthesis.
What is RNA?
RNA is ribonucleic acid and is found in all living cells. It acts as the messenger carrying
instructions from DNA for the synthesis of proteins.
Few viruses will have RNA as their genetic material.
What is codon?
Codon is a sequence of three nucleotides and they together form a unit of genetic code in either
DNA or RNA.
What is anticodon?
It is found on tRNA and it is a sequence of three nucleotides which forms a genetic code on
tRNA, and these anticodon is complementary to the codons found on messenger RNA.
What is a protein molecule?
During translation, when amino acids are added in a sequential manner, the condensation of
amino acids will form a peptide bond in between them and finally forms a polypeptide chain. It
is the DNA through mRNA directs the protein synthesis.
Point mutation
In point mutation, only one or very few nucleotides will be affected or mutated in a gene
sequence.
Frame shift mutation
Either insertions or deletion can result in frame shift mutation, due to th.
Chapter 8:
Microbial Genetics
*
Plasmids Exist in Cells Separate from Chromosomes
Big Picture: Genetics
The science of heredity
Central dogma of molecular biology
Mutations
Gene expression controlled by operons
Alteration of bacterial genes and/or gene expression
Cause of disease
Prevent disease treatment
Manipulated for human benefit
Big Picture: Genetics
Structure and Function of the Genetic Material
Learning Objectives
8-1 Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics.
8-2 Describe how DNA serves as genetic information.
8-3 Describe the process of DNA replication.
8-4 Describe protein synthesis, including transcription, RNA processing, and translation.
8-5 Compare protein synthesis in prokaryotes and eukaryotes.
Structure and Function of the Genetic Material
Genetics: the study of genes, how they carry information, how information is expressed, and how genes are replicated
Chromosomes: structures containing DNA that physically carry hereditary information; the chromosomes contain genes
Genes: segments of DNA that encode functional products, usually proteins
Genome: all the genetic information in a cell
Structure and Function of the Genetic Material The genetic code is a set of rules that determines how a nucleotide sequence is converted to an amino acid sequence of a proteinCentral dogma:
Genotype and Phenotype
Genotype: the genetic makeup of an organism
Phenotype: expression of the genes
DNA and Chromosomes
Bacteria usually have a single circular chromosome made of DNA and associated proteins
Short tandem repeats (STRs): repeating sequences of noncoding DNA
Figure 8.1 A Prokaryotic Chromosome
Chromosome
The Flow of Genetic Information
Vertical gene transfer: flow of genetic information from one generation to the next
Horizontal gene transfer: flow of genetic information between individuals of the SAME generation (see the middle portion of the next slide!)
Figure 8.2 The Flow of Genetic Information
Parent cell
DNA
Genetic information is used
within a cell to produce the
proteins needed for the cell
to function.
Genetic information can be
transferred horizontally between
cells of the same generation.
Genetic information can be
transferred vertically to the
next generation of cells.
New combinations
of genes
Translation
Cell metabolizes and grows
Recombinant cell
Offspring cells
Transcription
DNA Replication
DNA forms a double helix
“Backbone” consists of deoxyribose-phosphate
Two strands of nucleotides are held together by hydrogen bonds between A-T and C-G
Strands are antiparallel
Order of the nitrogen-containing bases forms the genetic instructions of the organism
DNA Replication
One strand serves as a template for the production of a second strand
Topoisomerase and gyrase relax the strands
Helicase separates the strands
A replication fork is created
DNA Replication
DNA poly ...
This presentation deals with the ‘Central Dogma’ which is briefly the process by which the instructions in DNA are converted into a functional product. It was first proposed in 1958 by Francis Crick, discoverer of the structure of DNA.
Resources of DNA synthesis and Protein synthesis are here: I got them from youtube,
https://www.youtube.com/watch?v=TNKWgcFPHqw
https://www.youtube.com/watch?v=2BwWavExcFI
Read| The latest issue of The Challenger is here! We are thrilled to announce that our school paper has qualified for the NATIONAL SCHOOLS PRESS CONFERENCE (NSPC) 2024. Thank you for your unwavering support and trust. Dive into the stories that made us stand out!
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
This presentation includes basic of PCOS their pathology and treatment and also Ayurveda correlation of PCOS and Ayurvedic line of treatment mentioned in classics.
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In Odoo, the chatter is like a chat tool that helps you work together on records. You can leave notes and track things, making it easier to talk with your team and partners. Inside chatter, all communication history, activity, and changes will be displayed.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
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How to Build a Module in Odoo 17 Using the Scaffold MethodCeline George
Odoo provides an option for creating a module by using a single line command. By using this command the user can make a whole structure of a module. It is very easy for a beginner to make a module. There is no need to make each file manually. This slide will show how to create a module using the scaffold method.
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Thinking of getting a dog? Be aware that breeds like Pit Bulls, Rottweilers, and German Shepherds can be loyal and dangerous. Proper training and socialization are crucial to preventing aggressive behaviors. Ensure safety by understanding their needs and always supervising interactions. Stay safe, and enjoy your furry friends!
2. Chapter 10 From DNA to Protein: Gene Expression
Key Concepts
• 10.1 Genetics Shows That Genes Code for
Proteins
• 10.2 DNA Expression Begins with Its
Transcription to RNA
• 10.3 The Genetic Code in RNA Is
Translated into the Amino Acid Sequences
of Proteins
3. Chapter 10 From DNA to Protein: Gene Expression
• 10.4 Translation of the Genetic Code is
Mediated by tRNA and Ribosomes
• 10.5 Proteins Are Modified after
Translation
4. Chapter 10 Opening Question
How do antibiotics such as tetracycline
target bacterial protein synthesis?
5. Concept 10.1 Genetics Shows That Genes Code for Proteins
Identification of a gene product as a protein
began with a mutation.
Garrod saw a disease phenotype—
alkaptonuria—occurring in children who
shared more alleles as first cousins.
A substance in their blood (HA)
accumulated—was not catalyzed—and the
gene for the enzyme was mutated.
Garrod correlated one gene to one enzyme.
6. Concept 10.1 Genetics Shows That Genes Code for Proteins
Phenylketonuria is another genetic disease
that involves this pathway.
The enzyme that converts phenylalanine to
tyrosine is nonfunctional.
Untreated, it can lead to mental retardation,
but is easily detected in newborns.
9. Concept 10.1 Genetics Shows That Genes Code for Proteins
Phenotypic expression of alkapatonuria and
phenylketonuria led to the one gene–one
protein hypothesis.
A mutant phenotype arises from a change in
the protein’s amino acid sequence.
However, the one gene–one protein
hypothesis proved too simple in studies of
human mutations.
10. Concept 10.1 Genetics Shows That Genes Code for Proteins
The gene–enzyme relationship has since
been revised to the one gene–one
polypeptide relationship.
Example: In hemoglobin, each polypeptide
chain is specified by a separate gene.
Other genes code for RNA but are not
translated to polypeptides; some genes
are involved in controlling other genes.
12. Concept 10.1 Genetics Shows That Genes Code for Proteins
Molecular biology is the study of nucleic
acids and proteins,and often focuses on
gene expression.
Gene expression to form a specific
polypeptide occurs in two steps:
• Transcription—copies information from a
DNA sequence (a gene) to a
complementary RNA sequence
• Translation—converts RNA sequence to
amino acid sequence of a polypeptide
13. Concept 10.1 Genetics Shows That Genes Code for Proteins
Roles of three kinds of RNA in protein
synthesis:
• Messenger RNA (mRNA) and
transcription—carries copy of a DNA
sequence to the site of protein synthesis at
the ribosome
• Ribosomal RNA (rRNA) and translation—
catalyzes peptide bonds between amino
acids
• Transfer RNA (tRNA) mediates between
mRNA and protein—carries amino acids
for polypeptide assembly
15. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Transcription—the formation of a specific
RNA sequence from a specific DNA
sequence—requires some components:
• A DNA template for base pairings—one of
the two strands of DNA
• Nucleoside triphosphates
(ATP,GTP,CTP,UTP) as substrates
• An RNA polymerase enzyme
16. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Besides mRNAs, other types of RNA are
produced by transcription:
• tRNA
• rRNA
• Small nuclear RNAs
• microRNAs
RNAs may have other functions in the cell
besides protein synthesis.
17. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
RNA polymerases catalyze synthesis of
RNA from the DNA template.
RNA polymerases are processive—a single
enzyme-template binding results in
polymerization of hundreds of RNA bases.
Unlike DNA polymerases, RNA
polymerases do not need primers.
19. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Transcription occurs in three phases:
• Initiation
• Elongation
• Termination
20. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Initiation requires a promoter—a special
sequence of DNA.
RNA polymerase binds to the promoter.
Promoter tells RNA polymerase two things:
• Where to start transcription
• Which strand of DNA to transcribe
Part of each promoter is the transcription
initiation site.
23. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Elongation: RNA polymerase unwinds DNA
about 13 base pairs at a time; reads
template in 3′-to-5′ direction.
RNA polymerase adds nucleotides to the 3′
end of the new strand.
The first nucleotide in the new RNA forms
its 5′ end and the RNA transcript is
antiparallel to the DNA template strand.
RNA polymerases can proofread, but allow
more mistakes.
25. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Termination is specified by a specific DNA
base sequence.
Mechanisms of termination are complex and
varied.
For some genes, the transcript falls away
from the DNA template and RNA
polymerase—for others a helper protein
pulls it away.
27. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Coding regions are sequences of a DNA
molecule that are expressed as proteins.
Eukaryotic genes may have noncoding
sequences—introns (intervening
regions).
The coding sequences are exons
(expressed regions).
Introns and exons appear in the primary
mRNA transcript—pre-mRNA; introns are
removed from the final mRNA.
30. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Nucleic acid hybridization reveals introns.
Target DNA is denatured, then incubated
with a probe—a nucleic acid strand from
another source.
If the probe has a complementary
sequence, a probe–target double helix—
called a hybrid—forms.
32. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Researchers using mature mRNA as the
probe saw loops where base pairing did
not occur in the DNA–RNA hybrid.
If pre-mRNA was used, the result was a
linear matchup—complete hybridization.
Introns were a part of the pre-mRNA, but
were removed before primary mRNA was
made.
34. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Introns interrupt, but do not scramble, the
DNA sequence that encodes a
polypeptide.
Sometimes, the separated exons code for
different domains (functional regions) of
the protein.
35. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
RNA splicing removes introns and splices
exons together.
Newly transcribed pre-mRNA is bound at
ends by snRNPs—small nuclear
ribonucleoprotein particles.
Consensus sequences are short
sequences between exons and introns,
bound by snRNPs.
36. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
Besides the snRNPs, other proteins are
added to form an RNA–protein complex,
the spliceosome.
The complex cuts pre-mRNA, releases
introns, and splices exons together to
produce mature mRNA.
38. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
In the disease β-thalassemia, a mutation
may occur at an intron consensus
sequence in the β-globin gene—the pre-
mRNA can not be spliced correctly.
Non-functional β-globin mRNA is produced,
which shows how mutations are used to
elucidate cause-and-effect relationships.
Alternative splicing results in different
mRNAs and different polypeptides from a
single gene.
39. Concept 10.2 DNA Expression Begins with Its Transcription to
RNA
While the pre-mRNA is in the nucleus it
undergoes two processing steps:
A 5′ cap (or G cap) is added to the 5′ end as
it is transcribed and facilitates binding and
prevents breakdown by enzymes.
A poly A tail is added to the 3′ end at the
end of transcription and assists in export
from the nucleus and aids stability.
40. Concept 10.3 The Genetic Code in RNA Is Translated into the
Amino Acid Sequences of Proteins
The genetic code—specifies which amino
acids will be used to build a protein
Codon—a sequence of three bases; each
codon specifies a particular amino acid
Start codon—AUG—initiation signal for
translation
Stop codons—UAA, UAG, UGA—stop
translation and polypeptide is released
43. Concept 10.3 The Genetic Code in RNA Is Translated into the
Amino Acid Sequences of Proteins
For most amino acids, there is more than
one codon; the genetic code is redundant.
The genetic code is not ambiguous—each
codon specifies only one amino acid.
The genetic code is nearly universal: the
codons that specify amino acids are the
same in all organisms.
Exceptions: Within mitochondria,
chloroplasts, and some protists, there are
differences.
44. Concept 10.3 The Genetic Code in RNA Is Translated into the
Amino Acid Sequences of Proteins
This common genetic code is a common
language for evolution.
The code is ancient and has remained intact
throughout evolution.
The common code also facilitates genetic
engineering.
45. Concept 10.3 The Genetic Code in RNA Is Translated into the
Amino Acid Sequences of Proteins
Mutations can also be defined in terms of
their effects on polypeptide sequences.
Silent mutations have no effect on amino
acids—often found in noncoding regions of
DNA.
A base substitution does not always affect
amino acid sequence, which may be
repaired in translation.
47. Concept 10.3 The Genetic Code in RNA Is Translated into the
Amino Acid Sequences of Proteins
Missense mutations are substitutions by one
amino acid for another in a protein.
Example: Sickle-cell disease—allele differs
from normal by one base pair
Missense mutations may result in a
defective protein, reduced protein
efficiency, or even a gain of function as in
the TP53 gene.
49. Concept 10.3 The Genetic Code in RNA Is Translated into the
Amino Acid Sequences of Proteins
Nonsense mutations involve a base
substitution that causes a stop codon to
form somewhere in the mRNA.
This results in a shortened protein, which is
usually not functional—if near the 3' end it
may have no effect.
51. Concept 10.3 The Genetic Code in RNA Is Translated into the
Amino Acid Sequences of Proteins
Frame-shift mutations are insertions or
deletions of bases in DNA.
These mutations interfere with translation
and shift the “reading-frame.”
Nonfunctional proteins are produced.
53. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
tRNA links information in mRNA codons
with specific amino acids.
For each amino acid, there is a specific type
or “species” of tRNA.
Two key events to ensure that the protein
made is the one specified by the mRNA:
• tRNAs must read mRNA codons correctly.
• tRNAs must deliver amino acids
corresponding to each codon.
54. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Each tRNA has three functions, made
possible by its structure and base
sequence:
• tRNAs bind to a particular amino acid, and
become “charged.”
• tRNAs bind at their midpoint—anticodon-to
mRNA molecules.
• tRNAs interacts with ribosomes.
56. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Wobble—specificity for the base at the 3′
end of the codon is not always observed.
Example: Codons for alanine—GCA, GCC,
and GCU—are recognized by the same
tRNA.
Wobble allows cells to produce fewer tRNA
species, but does not allow the genetic
code to be ambiguous.
58. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Activating enzymes—aminoacyl-tRNA
synthetases—charge tRNA with the
correct amino acids.
Each enzyme is highly specific for one
amino acid and its corresponding tRNA.
The enzymes have three-part active sites—
they bind a specific amino acid, a specific
tRNA, and ATP.
59. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Experiment by Benzer and others:
Cysteine already bound to tRNA was
chemically changed to alanine.
Which would be recognized—the amino
acid or the tRNA in protein synthesis?
Answer: Protein synthesis machinery
recognizes the anticodon, not the amino
acid
60. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
The translation of mRNA by tRNA is
accomplished at the ribosome—the
workbench—and holds mRNA and
charged tRNAs in the correct positions to
allow assembly of polypeptide chain.
Ribosomes are not specific; they can make
any type of protein.
61. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Ribosomes have two subunits, large and
small.
In eukaryotes, the large subunit has three
molecules of ribosomal RNA (rRNA) and
49 different proteins in a precise pattern.
The small subunit has one rRNA and 33
proteins.
63. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Large subunit has three tRNA binding sites:
A (amino acid) site binds with anticodon of
charged tRNA.
P (polypeptide) site is where tRNA adds its
amino acid to the growing chain.
E (exit) site is where tRNA sits before being
released from the ribosome.
64. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Ribosome has a fidelity function: when
proper binding occurs, hydrogen bonds
form between the base pairs.
Small subunit rRNA validates the match—if
hydrogen bonds have not formed between
all three base pairs, the tRNA must be an
incorrect match for that codon and the
tRNA is rejected.
65. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Like transcription, translation also occurs in
three steps:
• Initiation
• Elongation
• Termination
66. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Initiation:
An initiation complex consists of a
charged tRNA and small ribosomal
subunit, both bound to mRNA.
After binding, the small subunit moves along
the mRNA until it reaches the start codon,
AUG.
The first amino acid is always methionine,
which may be removed after translation.
67. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
The large subunit joins the complex; the
charged tRNA is now in the P site of the
large subunit.
Initiation factors are responsible for
assembly of the initiation complex from
mRNA, two ribosomal subunits and
charged tRNA.
70. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Elongation: The second charged tRNA
enters the A site
Large subunit catalyzes two reactions:
It breaks bond between tRNA in P site and
its amino acid.
A peptide bond forms between that amino
acid and the amino acid on tRNA in the A
site.
71. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
When the first tRNA has released its
methionine, it moves to the E site and
dissociates from the ribosome—it can then
become charged again.
Elongation occurs as the steps are
repeated, assisted by proteins called
elongation factors.
72. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
The large subunit has peptidyl transferase
activity—if rRNA is destroyed, the activity
stops.
The component with this activity is an rRNA
in the ribosome.
The catalyst is an example of a ribozyme
(from ribonucleic acid and enzyme).
75. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Termination—translation ends when a stop
codon enters the A site.
Stop codon binds a protein release factor—
allows hydrolysis of bond between
polypeptide chain and tRNA on the P site.
Polypeptide chain separates from the
ribosome—C terminus is the last amino
acid added.
79. Concept 10.4 Translation of the Genetic Code Is Mediated by
tRNA and Ribosomes
Several ribosomes can work together to
translate the same mRNA, producing
multiple copies of the polypeptide.
A strand of mRNA with associated
ribosomes is called a polyribosome, or
polysome.
80. Concept 10.5 Proteins Are Modified after Translation
Posttranslational aspects of protein
synthesis:
Polypeptide emerges from the ribosome and
folds into its 3-D shape.
Its conformation allows it to interact with
other molecules—it may contain a signal
sequence (or signal peptide) indicating
where in the cell it belongs.
81. Concept 10.5 Proteins Are Modified after Translation
In the absence of a signal sequence, the
protein will remain where it was made.
Some proteins contain signal sequences
that “target” them to the nucleus,
mitochondria, or other places.
Signal sequence binds to a receptor protein
on the organelle surface—a channel forms
and the protein moves into the organelle.
85. Concept 10.5 Proteins Are Modified after Translation
Protein modifications:
Proteolysis—cutting of a long polypeptide
chain, or polyprotein, into final products, by
proteases
Glycosylation—addition of carbohydrates
to form glycoproteins
Phosphorylation—addition of phosphate
groups catalyzed by protein kinases—
charged phosphate groups change the
conformation of the protein
87. Answer to Opening Question
Tetracyclines kill bacteria by interrupting
translation.
They bind to the small subunit of the
ribosome, which changes the ribosome
structure.
Charged tRNAs can no longer bind to the A
site on the ribosome.