Genetic Code Overview
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Genetic Code Overview

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Questions and Answers

What is the total number of codons in the genetic code?

  • 32
  • 20
  • 64 (correct)
  • 61

    • Which of the following statements about the genetic code is NOT true?

  • The genetic code is universal across organisms.
  • Each codon codes for only one amino acid.
  • Codons can contain punctuation for clarity. (correct)
  • Some amino acids are coded by more than one codon.

    • What feature of the genetic code allows for some amino acids to be represented by multiple codons?

  • Non-ambiguity
  • Linearity
  • Degeneracy (correct)
  • Universality

    • What type of codons do UAA, UAG, and UGA represent in the genetic code?

    <p>Nonsense codons</p> Signup and view all the answers

    How are the codons organized in a complete genetic code?

    <p>In order of their nucleotide sequence</p> Signup and view all the answers

    Which characteristic of the genetic code ensures that no codon overlaps with another?

    <p>Non-overlapping</p> Signup and view all the answers

    What is the purpose of the translation process in protein synthesis?

    <p>To translate nucleotide sequences into amino acid sequences</p> Signup and view all the answers

    What is the sequence direction in which codons are read during protein synthesis?

    <p>5' to 3'</p> Signup and view all the answers

    What is the initiation codon in the genetic code?

    <p>AUG</p> Signup and view all the answers

    Which of the following statements accurately describes a key feature of the genetic code?

    <p>The code is non-overlapping.</p> Signup and view all the answers

    How many codons in the genetic code do not code for amino acids?

    <p>3</p> Signup and view all the answers

    What is meant by the term 'degenerate code' in the context of the genetic code?

    <p>Multiple codons can code for the same amino acid.</p> Signup and view all the answers

    Which of the following characteristics is NOT associated with the genetic code?

    <p>It is a four-letter code.</p> Signup and view all the answers

    Which codon always initiates protein synthesis in eukaryotes?

    <p>AUG</p> Signup and view all the answers

    What does it mean for the genetic code to be 'commaless'?

    <p>There are no spaces between codons.</p> Signup and view all the answers

    In prokaryotes, what is the modified form of methionine involved in protein synthesis?

    <p>Formylmethionine</p> Signup and view all the answers

    Which statement regarding triplet codons is correct?

    <p>Each codon consists of three bases.</p> Signup and view all the answers

    What is meant by the degeneracy of the genetic code?

    <p>An amino acid can be coded by multiple codons.</p> Signup and view all the answers

    Which of the following codons functions as the initiator codon in protein synthesis?

    <p>AUG</p> Signup and view all the answers

    What characteristic do all codons share across different species?

    <p>They are the same for the same amino acid.</p> Signup and view all the answers

    What role do terminator codons play in protein synthesis?

    <p>They signal the end of protein synthesis.</p> Signup and view all the answers

    How does the Wobble Hypothesis explain certain codons encoding the same amino acid?

    <p>By varying the third position of the codon.</p> Signup and view all the answers

    Which of the following statements best describes the characteristic of the genetic code being 'unambiguous'?

    <p>One codon specifies only one amino acid.</p> Signup and view all the answers

    Why is redundancy in the genetic code advantageous?

    <p>Redundancy prevents mutations from affecting protein function.</p> Signup and view all the answers

    Which mitochondrial codon exceptions indicate amino acids instead of termination?

    <p>AUA - methionine</p> Signup and view all the answers

    What is the result when the RNA sequence AAAAAA is used in the experiments?

    <p>Peptide of lysine</p> Signup and view all the answers

    What role do release factors play in protein synthesis termination?

    <p>They bind to stop codons</p> Signup and view all the answers

    In Nirenberg and Matthaei's experiments, what was used to determine the amino acids specified by different codons?

    <p>RNA sequences made up of varying bases</p> Signup and view all the answers

    What happens to the polypeptide chain during the termination of translation?

    <p>It is released from the ribosome</p> Signup and view all the answers

    Which of the following codons is a termination codon in the cytoplasm?

    <p>UGA</p> Signup and view all the answers

    What was the significance of studying codons composed of only one type of base in the experiments?

    <p>To clarify the relationship between codon and amino acid</p> Signup and view all the answers

    Which amino acid corresponds to the RNA sequence CCCCCC according to the experiments?

    <p>Peptide for proline</p> Signup and view all the answers

    What is the role of initiation factor 3 (IF-3) in the initiation of translation?

    <p>It prevents the large subunit from associating with the small subunit.</p> Signup and view all the answers

    Which component forms a complex with initiation factor 2 (IF-2) during the initiation of translation?

    <p>A tRNA charged with N-formylmethionine</p> Signup and view all the answers

    What occurs when GTP is hydrolyzed during the initiation of translation?

    <p>Initiation factors dissociate from the complex.</p> Signup and view all the answers

    What is the final result after the large subunit binds to the initiation complex?

    <p>Formation of a complete 70S initiation complex.</p> Signup and view all the answers

    During translation termination, what happens to the polypeptide chain?

    <p>It is released from the tRNA in the P site.</p> Signup and view all the answers

    What is the significance of the 70S initiation complex in translation?

    <p>It allows the ribosome to initiate translation successfully.</p> Signup and view all the answers

    How is the release factor involved in the process of translation termination?

    <p>It binds to the A site and releases the polypeptide chain.</p> Signup and view all the answers

    What prevents the large ribosomal subunit from immediately associating with the small subunit during translation initiation?

    <p>The binding of initiation factor 3 (IF-3).</p> Signup and view all the answers

    Study Notes

    Genetic Code

    • Genetic code is a set of rules that translates a sequence of nucleotides in DNA or RNA into a sequence of amino acids in a protein.
    • It is a dictionary with codons as the words.
    • Each codon is a triplet of nucleotides, and there are 64 possible codons.
    • Three codons are non-sense codons, which do not code for any amino acid.
    • The other 61 codons code for the 20 amino acids.

    Genetic Code Table

    • The genetic code table shows the correspondence between codons and amino acids.
    • The table is organized by the first, second and third bases of the codon.

    Features of the Genetic Code

    • Universal: The same codons code for the same amino acids in all organisms.
    • Non-ambiguous: Each codon codes for only one amino acid.
    • Comma-less: Codons are read consecutively without punctuation.
    • Degenerate: More than one codon can code for the same amino acid.
    • Non-overlapping: Three consecutive bases code for one amino acid.
    • Initiation codon: AUG is the start codon, which codes for methionine.
    • Termination codons: UAA, UAG, and UGA are stop codons, which signal the end of protein synthesis.

    Redundancy of the Genetic Code

    • Different codons can specify the same amino acid.
    • This is due to the degeneracy of the code.
    • This makes it less likely that mutations will disrupt protein synthesis.

    Complementary Base Pairing

    • The three base codons on mRNA are complementary to the three base anticodons of tRNA.
    • This is how tRNA molecules deliver the correct amino acid to the ribosome.

    Wobble Hypothesis

    • Proposed by Crick to explain how tRNA can recognize multiple codons.
    • The third base in a codon can sometimes "wobble" or pair with more than one base in an anticodon.
    • This allows for a limited level of flexibility in the codon-anticodon pairing.
    • Allows cells to have fewer tRNAs than codons.

    Universal

    • The same codons specify the same amino acids in all species.

    Terminator codons

    • Three "nonsense" codons, UAA, UAG, and UGA, act as termination codons.
    • They signal the end of protein synthesis.

    Initiator codon

    • AUG is typically the initiation codon.
    • It codes for methionine.

    Genetic Code - Universal

    • The genetic code is universal with some exceptions.
    • Mitochondrial codons have some differences compared to cytoplasmic codons.

    Nirenberg & Matthaei experiments

    • These experiments used synthetic mRNA to determine what amino acids were coded by different codons.
    • They found that the codon UUU codes for phenylalanine, AAA for lysine, and CCC for proline.

    Ribosome

    • The ribosome is the site of protein synthesis.
    • It has two subunits: a small subunit and a large subunit.
    • The small subunit binds to mRNA and the large subunit binds to tRNA.

    Nirenberg-Leder Experiment

    • Used a filter-binding assay to determine the codons that code for specific amino acids.
    • The experiment involved preparing a cell extract containing ribosomes, tRNAs, and amino acids.
    • They added different synthetic mRNA sequences to the extract, and analyzed the results.

    Protein Synthesis Termination

    • Stop codons signal the end of protein synthesis.
    • Release factors bind to the stop codons and cause the polypeptide chain to be released from the ribosome.
    • Hydrolysis of GTP releases the release factors and the tRNA from the ribosome.

    Initiation of Translation

    • The ribosome is made up of two subunits: a small subunit and a large subunit.
    • Initiation factor 3 (IF-3) prevents the large subunit from associating with the small subunit.
    • The small subunit binds to the mRNA.
    • A tRNA charged with N-formylmethionine binds to the initiation codon on the mRNA.
    • The large subunit binds to the complex, creating a complete initiation complex.

    Nirenberg-Leder Experiment

    • Used a filter-binding assay to determine the codons that code for specific amino acids.
    • The experiment involved preparing a cell extract containing ribosomes, tRNAs, and amino acids.
    • They added different synthetic mRNA sequences to the extract, and analyzed the results.

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    Genetic Code PDF

    Description

    This quiz delves into the genetic code, exploring its structure and function in the translation of nucleotides to amino acids. Understand the universal nature, non-ambiguous definitions, and the organization of the genetic code table. Test your knowledge on codons and their corresponding amino acids.

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