Major Principles of Translation and Protein Synthesis
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Questions and Answers

How many distinct codons are present in the genetic code?

  • 64 (correct)
  • 32
  • 256
  • 128

    • What is the significance of codons in the genetic code?

  • Codons perform enzymatic functions.
  • Codons represent amino acids. (correct)
  • Codons are used for energy storage.
  • Codons are sequences of DNA only.

    • In the context of protein synthesis, what does each codon correspond to?

  • A specific lipid
  • A specific sugar molecule
  • A specific amino acid (correct)
  • A specific nucleic acid

    • Which of the following statements about the genetic code is true?

    <p>Each codon is three nucleotides long.</p> Signup and view all the answers

    What largest function does the genetic code serve in living organisms?

    <p>It guides protein synthesis.</p> Signup and view all the answers

    What characterizes the primary structure of a polypeptide?

    <p>It is a linear sequence of amino acids.</p> Signup and view all the answers

    How many amino acids can the primary structure of a typical polypeptide contain?

    <p>It can consist of a few hundred to a couple of thousand amino acids.</p> Signup and view all the answers

    What role does the primary structure play in the overall function of a protein?

    <p>It determines the protein's final 3D shape.</p> Signup and view all the answers

    Which of the following statements about the primary structure of a polypeptide is incorrect?

    <p>It remains unchanged during the protein's lifetime.</p> Signup and view all the answers

    Which component is crucial for forming the primary structure of a polypeptide?

    <p>Amino acids</p> Signup and view all the answers

    What unit is used to describe the sedimentation coefficient in centrifugation?

    <p>Svedberg units</p> Signup and view all the answers

    Who invented the ultracentrifuge, which is linked to the sedimentation coefficient?

    <p>Theodor Svedberg</p> Signup and view all the answers

    How do the ribosomal subunits combine to form a complete ribosome?

    <p>30S and 50S</p> Signup and view all the answers

    What is the total Svedberg value of the ribosome formed by the combination of its subunits?

    <p>70S</p> Signup and view all the answers

    Which of the following pairings of ribosomal subunits is incorrect?

    <p>20S and 30S</p> Signup and view all the answers

    What is one primary function of a tRNA molecule during translation?

    <p>It recognizes a three-base codon sequence in mRNA.</p> Signup and view all the answers

    Which aspect of tRNA is essential for its role in translation?

    <p>Its recognition of three-base codon sequences in mRNA.</p> Signup and view all the answers

    What happens if a tRNA does not recognize the correct codon during translation?

    <p>It could result in the incorporation of incorrect amino acids into the protein.</p> Signup and view all the answers

    Which of the following statements accurately describes the relationship between tRNA and mRNA?

    <p>tRNA recognizes mRNA codons and delivers corresponding amino acids.</p> Signup and view all the answers

    During the translation process, the codon recognized by tRNA is composed of how many bases?

    <p>Three bases.</p> Signup and view all the answers

    What is a key difference between prokaryotic and eukaryotic translation?

    <p>Prokaryotic translation begins before the mRNA transcript is completed.</p> Signup and view all the answers

    In which cellular context does translation occur simultaneously with mRNA transcription?

    <p>In bacterial cells.</p> Signup and view all the answers

    Which statement accurately describes eukaryotic translation?

    <p>It requires splicing of the mRNA before translation.</p> Signup and view all the answers

    Which process is distinct in prokaryotic translation compared to eukaryotic translation?

    <p>The initiation of translation before transcription completion.</p> Signup and view all the answers

    Why is the initiation of translation before mRNA completion significant in prokaryotes?

    <p>It allows for faster protein synthesis.</p> Signup and view all the answers

    What occurs after RF1 (or RF2) and RF3 have bound during the process of protein synthesis?

    <p>The bond between the polypeptide and the tRNA is hydrolyzed.</p> Signup and view all the answers

    What is the result of the bond hydrolysis between the polypeptide and tRNA?

    <p>The polypeptide and tRNA are released from the ribosome.</p> Signup and view all the answers

    Which factor is essential for the hydrolysis of the bond between the polypeptide and tRNA?

    <p>The presence of RF3 after RF1 and RF2.</p> Signup and view all the answers

    During which stage of protein synthesis does the hydrolysis of the tRNA-polypeptide bond occur?

    <p>Termination of translation.</p> Signup and view all the answers

    What happens to the ribosome after the polypeptide and tRNA are released?

    <p>It may initiate a new round of translation with a new mRNA.</p> Signup and view all the answers

    What is located at the amino-terminal end of a polypeptide?

    <p>Amino group (NH3+)</p> Signup and view all the answers

    Which statement accurately describes the codon associated with the first amino acid in a polypeptide?

    <p>It is positioned near the 5′ end of the mRNA.</p> Signup and view all the answers

    What is the significance of the N-terminus in a polypeptide?

    <p>It indicates the starting point for translation.</p> Signup and view all the answers

    Which of the following statements about the first amino acid in a polypeptide is false?

    <p>It is found at the carboxyl-terminal end.</p> Signup and view all the answers

    In the context of polypeptide synthesis, what does the term 'N-terminus' refer to?

    <p>The start of the chain with a free amino group.</p> Signup and view all the answers

    What are the names given to the twenty-first and twenty-second amino acids in polypeptides?

    <p>Selenocysteine and Pyrrolysine</p> Signup and view all the answers

    Which characteristic best describes the roles of Selenocysteine and Pyrrolysine in proteins?

    <p>They are non-standard amino acids with essential roles in specific enzymes.</p> Signup and view all the answers

    In what context can Selenocysteine and Pyrrolysine be classified compared to the standard amino acids?

    <p>They are encoded by unique codons not present in the universal genetic code.</p> Signup and view all the answers

    Which statement is accurate regarding the integration of Selenocysteine and Pyrrolysine into polypeptides?

    <p>They are incorporated into polypeptides through different synthetases than standard amino acids.</p> Signup and view all the answers

    Which of the following statements best exemplifies the significance of Selenocysteine and Pyrrolysine in biological systems?

    <p>Their presence allows enzymes to carry out reactions that are otherwise impossible.</p> Signup and view all the answers

    What does the sequence of three bases in a codon specifically determine?

    <p>A specific amino acid</p> Signup and view all the answers

    Which of the following statements about codons is incorrect?

    <p>Each codon codes for multiple amino acids</p> Signup and view all the answers

    How many total bases comprise the series of three bases found in a single codon?

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

    Which aspect of protein synthesis depends on the sequence of codons?

    <p>The assembly of amino acids into a polypeptide</p> Signup and view all the answers

    What is the primary function of codons in the process of translation?

    <p>To specify the order of amino acids</p> Signup and view all the answers

    What structural role do irregularly shaped segments play in proteins?

    <p>They connect α-helical and β-sheet regions to define tertiary structure.</p> Signup and view all the answers

    Which feature is essential for the tertiary structure of proteins?

    <p>Connections between distinct secondary structures.</p> Signup and view all the answers

    In terms of protein structure, how can the connection of α-helices and β-sheets be best described?

    <p>Irregularly shaped segments mediate their connection.</p> Signup and view all the answers

    What distinguishes the connections between α-helical and β-sheet regions in proteins?

    <p>They involve irregularly shaped segments.</p> Signup and view all the answers

    Which of the following best describes the significance of irregularly shaped segments in tertiary structure?

    <p>They provide flexibility and variety in protein shape.</p> Signup and view all the answers

    Study Notes

    Major Principles of Translation

    • Translation is the process where mRNA's codon sequence dictates the amino acid sequence synthesis of a polypeptide.
    • One or more polypeptides fold and assemble into a functional protein.
    • Proteins are essential for cell structure and function.
    • DNA stores the information for all the proteins an organism makes.
    • Genes that encode an amino acid sequence are known as protein-encoding genes or structural genes.
    • The RNA transcribed from protein-encoding genes is called messenger RNA (mRNA).

    The Genetic Basis For Protein Synthesis

    • Genetic material encodes the production of cellular proteins at the correct time and in suitable quantities.
    • Enzymes, a type of protein, catalyze specific chemical reactions.
    • All proteins are encoded by genes.
    • Some proteins are composed of two or more polypeptides.
    • One gene can encode two or more polypeptides due to alternative splicing.

    The Sequence of a Protein-Encoding Gene Provides a Template

    • The sequence of a gene provides a template for mRNA synthesis.
    • mRNA contains the information for polypeptide synthesis.
    • Translation interprets mRNA's nucleotide sequence into proteins' amino acid sequence.
    • mRNA sequences are read in groups of three nucleotides called codons.

    The Genetic Code Table

    • Each codon specifies a specific amino acid or signals the termination of translation.
    • The genetic code is a set of rules that dictates how mRNA codons specify amino acids.
    • The genetic code is degenerate (more than one codon can specify the same amino acid.)
    • The sequence of bases in mRNA determines coded information that is read in groups of three nucleotides called codons.

    The Sequence of Three Bases in Most Codons Specifies a Particular Amino Acid

    • Particular amino acids, for example, the codon AGC specifies serine while GGG encodes glycine.
    • The codon AUG specifies methionine and is used as a start codon.
    • Three codons (UAA, UAG, and UGA) are used to end translation and are known as stop codons or nonsense codons.

    The Genetic Code is Composed of 64 Different Codons

    • Polypeptides are composed of 20 different amino acids.
    • A code with two bases in a codon would not be sufficient to specify all 20 amino acids.
    • A three-base codon system forms 64 different codons, meaning many more codons exist than necessary to encode the 20 amino acids.
    • The genetic code is degenerate; multiple codons can be synonymous.

    The Third Base in Most Codons is Often Variable

    • The third base (wobble base) in codons often dictates specificity in the amino acid.
    • Common properties are found in this region, such as the capacity to pair with more than one base.

    The Polypeptide Chain

    • Polypeptide synthesis is directional, paralleling mRNA's codons order.
    • A peptide bond is formed between the carboxyl group of the last amino acid in the polypeptide and the amino group of the next amino acid.
    • This occurs via a condensation reaction which results in the release of a water molecule.
    • The newest amino acid added to a growing polypeptide always has a free carboxyl group.
    • The first amino acid in a polypeptide is at the amino terminal end (N-terminus).
    • The last amino acid is at the carboxyl-terminal end (C-terminus).
    • The chemical properties of amino acids dictate folding patterns.

    Ribosome Structure and Assembly

    • Ribosomes are macromolecules located in the cytoplasm.
    • Ribosomes consist of large and small subunits that assemble.
    • Bacterial cells have one ribosome type, Eukaryotes have multiple types and locations in the cytoplasm, and mitochondria.
    • Ribosomes contain A, P, and E sites where tRNA molecules bind.
    • mRNA lies on the 30S subunit, and polypeptide exits through a channel within the 50S subunit.
    • The 30S and 50S subunits form a 70S ribosome in bacteria.
    • Eukaryotic ribosomes are 80S.

    Stages of Translation

    • Translation has three stages: initiation, elongation, and termination.
    • Initiation involves the ribosomal subunits, mRNA, and initiator tRNA, assembling to form a complex.
    • Elongation is the ribosome sliding over the mRNA reading codons one at a time with peptide bond formation.
    • Termination occurs when a stop codon is reached, and the polypeptide is released.
    • Release factors recognize stop codons, triggering polypeptide release from the tRNA.

    Aminoacyl-tRNA Synthetases

    • Aminoacyl-tRNA synthetase enzymes attach amino acids to their corresponding tRNA molecules.
    • Each amino acid has a specific enzyme. An example is alanyl-tRNA synthetase that recognizes a tRNA with an alanine anticodon.
    • The enzyme participates in a chemical reaction, utilizing amino acids, tRNA, and ATP as molecules.

    Structure and Function of tRNA

    • tRNA molecules recognize mRNA codons and carry the corresponding amino acids.
    • Anticodons in tRNA are complementary to mRNA codons.
    • The anticodon in a tRNA is complementary to the codon for the amino acid.
    • The secondary structure of a tRNA resembles a cloverleaf pattern.
    • tRNA carries an amino acid at the 3' end.

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    Lecture 11: Molecular Biology I, BIO316 PDF

    Description

    This quiz covers the essential principles of translation and the genetic basis for protein synthesis. It explores the roles of mRNA, polypeptides, and the importance of proteins in cellular functions. Test your understanding of how genetic material influences protein production.

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