Protein Synthesis

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Questions and Answers

Which direction does translation proceed in?

  • From the amino to the carboxyl terminus (correct)
  • From the 5'-to-3' direction
  • From the carboxyl to the amino terminus
  • From the 3'-to-5' direction

What is the start codon for all protein synthesis?

  • UAA
  • UGA
  • UAG
  • AUG (correct)

What do specific stop codons signal during translation?

  • The start of translation
  • The presence of a specific tRNA
  • The end of translation (correct)
  • The presence of a specific amino acid

What is the process called when specific amino acid side chains are modified after translation?

<p>Posttranslational modification (C)</p> Signup and view all the answers

What is the enzyme responsible for covalently linking amino acids to tRNA?

<p>Aminoacyl-tRNA synthetase (C)</p> Signup and view all the answers

What is the process called when proteins are marked for degradation?

<p>Ubiquitination (A)</p> Signup and view all the answers

Which molecule carries the appropriate amino acid to the site of synthesis on the ribosomal complex?

<p>tRNA (B)</p> Signup and view all the answers

What is the function of aminoacyl-tRNA synthetases?

<p>To catalyze the attachment of amino acids to tRNA (D)</p> Signup and view all the answers

What molecule carries the code in triplicate?

<p>mRNA (B)</p> Signup and view all the answers

What are the components required for translation?

<p>Amino acids, tRNA, mRNA, rRNA, protein factors (A)</p> Signup and view all the answers

How many codons code for termination/stop codons?

<p>Three (B)</p> Signup and view all the answers

What is the consequence of altering the nucleotide sequence in the coding region of mRNA?

<p>All of the above (D)</p> Signup and view all the answers

Which family of enzymes is required for attaching amino acids to tRNA?

<p>Aminoacyl-tRNA synthetases (A)</p> Signup and view all the answers

What is the function of the editing activity of aminoacyl-tRNA synthetases?

<p>To remove incorrect amino acids from the enzyme or tRNA (A)</p> Signup and view all the answers

What is the cellular location of free ribosomes in eukaryotes?

<p>Cytosol (B)</p> Signup and view all the answers

What is the role of initiation factors in translation?

<p>All of the above (D)</p> Signup and view all the answers

What is the mechanism by which tRNA recognizes more than one codon for a specific amino acid?

<p>Wobble hypothesis (B)</p> Signup and view all the answers

Which initiation mechanism is used by eukaryotes to recognize the start codon?

<p>5'-cap (A)</p> Signup and view all the answers

Which codon on mRNA signals the start of protein synthesis and codes for methionine?

<p>AUG (A)</p> Signup and view all the answers

Which of the following codons on mRNA signals the end of protein synthesis and does not code for an amino acid?

<p>UAA (D)</p> Signup and view all the answers

What is the role of the Shine-Dalgarno sequence in translation initiation in prokaryotes?

<p>It aids in translation initiation. (D)</p> Signup and view all the answers

What is the role of the mRNA cap and poly-A tail in translation initiation in eukaryotes?

<p>They aid in translation initiation. (A)</p> Signup and view all the answers

Which protein factors are involved in the initiation, elongation, and termination of protein translation?

<p>RF 1/2 (prok) and eRF (euk) (C)</p> Signup and view all the answers

How do frameshift, missense, and nonsense gene mutations alter the reading frame of the mRNA and the protein synthesized from it?

<p>They alter the reading frame and the protein. (C)</p> Signup and view all the answers

Which of the following is true about the initiation codon?

<p>The initiation codon is recognized by tRNAi (D)</p> Signup and view all the answers

What distinguishes tRNAi from internal AUG-tRNA?

<p>tRNAi goes directly to P-site (D)</p> Signup and view all the answers

What does bacterial tRNAi carry?

<p>Bacterial tRNAi carries N-formylated methionine (fMet) (B)</p> Signup and view all the answers

What prevents the premature binding of the large subunit during initiation?

<p>IF-3 (prok) and eIF-3 (euk) (C)</p> Signup and view all the answers

What is the role of EF-Tu-GTP in elongation?

<p>EF-Tu-GTP facilitates delivery of charged tRNA for the next mRNA codon located in the A-site (D)</p> Signup and view all the answers

What determines how a protein will fold?

<p>Primary linear amino acid sequence (B)</p> Signup and view all the answers

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Study Notes

Translation Process

  • Translation proceeds in the 5' to 3' direction.
  • The start codon for all protein synthesis is AUG, which codes for methionine.
  • Specific stop codons (UAG, UAA, UGA) signal the termination of protein synthesis during translation.
  • The process of modifying specific amino acid side chains after translation is called post-translational modification.

tRNA and Amino Acids

  • The enzyme responsible for covalently linking amino acids to tRNA is aminoacyl-tRNA synthetase.
  • The molecule that carries the appropriate amino acid to the site of synthesis on the ribosomal complex is tRNA.
  • Aminoacyl-tRNA synthetases attach amino acids to tRNA and edit for correct pairing.
  • The family of enzymes required for attaching amino acids to tRNA is aminoacyl-tRNA synthetases.

mRNA and Codons

  • The molecule that carries the code in triplicate is mRNA.
  • The components required for translation are mRNA, tRNA, ribosomes, amino acids, and energy.
  • There are three codons (UAG, UAA, UGA) that code for termination/stop codons.

Consequences of Mutations

  • Altering the nucleotide sequence in the coding region of mRNA can change the amino acid sequence of the protein.
  • Frameshift, missense, and nonsense gene mutations can alter the reading frame of the mRNA and the protein synthesized from it.

Initiation and Elongation

  • Initiation factors play a crucial role in translation initiation.
  • The mechanism by which tRNA recognizes more than one codon for a specific amino acid is through wobble base pairing.
  • Eukaryotes use the scanning mechanism to recognize the start codon.
  • The AUG codon on mRNA signals the start of protein synthesis and codes for methionine.
  • The codon UAA on mRNA signals the end of protein synthesis and does not code for an amino acid.

Prokaryotes and Eukaryotes

  • The Shine-Dalgarno sequence is involved in translation initiation in prokaryotes.
  • The mRNA cap and poly-A tail are involved in translation initiation in eukaryotes.
  • Free ribosomes are found in the cytoplasm of eukaryotes.

Protein Synthesis and Folding

  • Protein factors involved in initiation, elongation, and termination of protein translation include initiation factors, EF-Tu-GTP, and release factors.
  • The sequence of amino acids determines how a protein will fold.
  • The initiation codon is recognized by the ribosome and plays a crucial role in translation initiation.
  • tRNAi is distinguished from internal AUG-tRNA by its ability to initiate protein synthesis.
  • Bacterial tRNAi carries methionine.
  • The 30S subunit prevents the premature binding of the large subunit during initiation.
  • EF-Tu-GTP plays a crucial role in elongation by bringing aminoacyl-tRNA to the ribosome.

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