Protein Metabolism I

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| By Michael Kagan
Michael Kagan, Anesthesiology
Michael serves as a Staff Anesthesiologist and Pain Management Physician at the U.S. Department of Veterans Affairs, dedicating his skills and expertise to support the healthcare needs of veterans.
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Protein Metabolism I - Quiz

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Questions and Answers
  • 1. 

    Which of these RNA species is the most abundant in translation?

    • A.

      TRNA

    • B.

      MRNA

    • C.

      RRNA

    Correct Answer
    C. RRNA
    Explanation
    rRNA, or ribosomal RNA, is the most abundant RNA species in translation. It makes up the majority of the ribosome, the cellular machinery responsible for protein synthesis. During translation, rRNA provides the structural framework for the ribosome and catalyzes the formation of peptide bonds between amino acids. It plays a crucial role in the assembly and functioning of the ribosome, making it essential for protein synthesis. mRNA, or messenger RNA, carries the genetic information from DNA to the ribosome, while tRNA, or transfer RNA, brings amino acids to the ribosome during translation. However, rRNA is the most abundant and essential RNA species in this process.

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  • 2. 

    Which of these are stop codons?

    • A.

      UAA

    • B.

      UGA

    • C.

      AUC

    • D.

      UAG

    • E.

      UGG

    Correct Answer(s)
    A. UAA
    B. UGA
    D. UAG
    Explanation
    The given options UAA, UGA, and UAG are stop codons. In the genetic code, stop codons signal the end of protein synthesis. When a ribosome encounters a stop codon during translation, it releases the newly synthesized protein and the process terminates. UAA, UGA, and UAG are recognized as stop codons by the ribosome, and they do not code for any amino acids. Thus, they play a crucial role in determining the length and functionality of proteins.

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  • 3. 

    Which of these anticodon bases can bind with the 3' codon base A U and C?

    • A.

      A

    • B.

      U

    • C.

      I

    • D.

      G

    • E.

      C

    Correct Answer
    C. I
  • 4. 

    AUG is designated for which amino acid (which also starts all protein synthesis)?

    • A.

      Cys

    • B.

      Asn

    • C.

      Phe

    • D.

      Met

    Correct Answer
    D. Met
    Explanation
    The correct answer is Met. AUG is the start codon in the genetic code and it codes for the amino acid methionine (Met). Methionine is the first amino acid in most proteins and it initiates protein synthesis.

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  • 5. 

    How is the anticodon for 5' CGC 3' read?

    • A.

      GCI

    • B.

      ICG

    Correct Answer
    B. ICG
    Explanation
    The anticodon for 5' CGC 3' is read as ICG. In the anticodon, the nucleotide sequence is read in the opposite direction to the mRNA codon. So, the first nucleotide in the anticodon is the third nucleotide in the mRNA codon, the second nucleotide in the anticodon is the second nucleotide in the mRNA codon, and the third nucleotide in the anticodon is the first nucleotide in the mRNA codon. Therefore, the anticodon for 5' CGC 3' is ICG.

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  • 6. 

    Which mutation changes the codon to a stop codon?

    • A.

      Silent

    • B.

      Nonsense

    • C.

      Missense

    • D.

      Radioactive spider bite

    Correct Answer
    B. Nonsense
    Explanation
    A nonsense mutation is the type of mutation that changes a codon, which is a sequence of three nucleotides in DNA, to a stop codon. Stop codons signal the end of protein synthesis, so when a codon is changed to a stop codon, it prematurely terminates the protein synthesis process. This can result in a nonfunctional or truncated protein being produced. Silent mutations do not change the amino acid sequence, missense mutations change one amino acid to another, and radioactive spider bite is not a type of mutation.

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  • 7. 

    Which mutation changes the codon to code for another amino acid?

    • A.

      Silent

    • B.

      Nonsense

    • C.

      Missense

    • D.

      Radioactive spider bite

    Correct Answer
    C. Missense
    Explanation
    A missense mutation is a type of genetic mutation that changes a single nucleotide in the DNA sequence, resulting in the substitution of one amino acid for another during protein synthesis. This change in the codon alters the genetic code, causing the protein to be produced with a different amino acid sequence. As a result, the function and structure of the protein may be affected, potentially leading to various physiological consequences or diseases.

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  • 8. 

    Which of the following in prokaryotes are orthologs in eukaryotes?

    • A.

      5S rRNA; 5S rRNA

    • B.

      5S rRNA; 5.8S rRNA

    • C.

      23S rRNA; 28S rRNA

    • D.

      16S rRNA; 18S rRNA

    • E.

      18S rRNA; 28S rRNA

    Correct Answer(s)
    B. 5S rRNA; 5.8S rRNA
    C. 23S rRNA; 28S rRNA
    D. 16S rRNA; 18S rRNA
    Explanation
    The answer is 5S rRNA; 5.8S rRNA, 23S rRNA; 28S rRNA, and 16S rRNA; 18S rRNA. In prokaryotes, the 5S rRNA is orthologous to the 5.8S rRNA in eukaryotes. Similarly, the 23S rRNA in prokaryotes is orthologous to the 28S rRNA in eukaryotes. Lastly, the 16S rRNA in prokaryotes is orthologous to the 18S rRNA in eukaryotes. Orthologs are genes in different species that evolved from a common ancestral gene and have similar functions.

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  • 9. 

    Aminoacylation of tRNA by aminoacyl-tRNA synthetases works in two steps: 1.  Amino acid activation by ________ with the release of phosphate ions. 2.  Binding of the activated amino acid to terminal A residue of the tRNA with release of ________.

    • A.

      GTP; AMP

    • B.

      AMP; ATP

    • C.

      ATP; AMP

    Correct Answer
    C. ATP; AMP
    Explanation
    Aminoacylation of tRNA by aminoacyl-tRNA synthetases works in two steps. First, the amino acid is activated by ATP, which results in the release of phosphate ions. Then, the activated amino acid is bound to the terminal A residue of the tRNA, resulting in the release of AMP. This process ensures that the correct amino acid is attached to the appropriate tRNA molecule, allowing for accurate protein synthesis.

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  • 10. 

    During the removal of coupling errors, the correct amino acid will not be able to fit into the editing site

    • A.

      True

    • B.

      False

    Correct Answer
    A. True
    Explanation
    During the removal of coupling errors, the correct amino acid will not be able to fit into the editing site because the editing site is specifically designed to accommodate the incorrect amino acid. This ensures that only the incorrect amino acid is removed, allowing the correct amino acid to be added to the growing polypeptide chain.

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  • 11. 

    The role is formylation is that methionyl-tRNA fmet cannot be inserted into the ____________ of a growing peptide.

    Correct Answer
    interior
    inside
    Explanation
    The correct answer is "interior, inside". The role of formylation is to prevent the insertion of methionyl-tRNA fmet into the interior or inside of a growing peptide. Formylation adds a formyl group to the methionine residue, which prevents it from being incorporated into the peptide chain. This modification ensures that the methionine is only used as the initiator amino acid at the beginning of protein synthesis.

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  • 12. 

    Before translation starts in prokaryotes two things need to happen pairing of mRNA with the 3' end of the ______ rRNA mediated by the __________ sequence, and pairing of mRNA initiation codon with ___________ of initiator tRNA molecule.

    • A.

      16S Shine Delgarno, codon

    • B.

      16S, Shine Delgarno; anticodon

    • C.

      5S; Shine Delgarno; anticodon

    • D.

      18S; Shine delgarno; anticodon

    Correct Answer
    B. 16S, Shine Delgarno; anticodon
    Explanation
    Before translation starts in prokaryotes, two things need to happen. The first is the pairing of mRNA with the 3' end of the 16S rRNA mediated by the Shine Delgarno sequence. The second is the pairing of the mRNA initiation codon with the anticodon of the initiator tRNA molecule.

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  • 13. 

    _________ prevents the 30S and 50S subunit from combining prematurely in bacterial translation, and _____ prevents the use of the A site in the initiation.

    • A.

      IF3; IF2

    • B.

      IF3; IF1

    • C.

      IF1; IF3

    • D.

      IF2; IF1

    Correct Answer
    B. IF3; IF1
    Explanation
    IF3 prevents the 30S and 50S subunit from combining prematurely in bacterial translation. This is important because the premature combination of these subunits could lead to the formation of non-functional or incorrect proteins. On the other hand, IF1 prevents the use of the A site in the initiation. The A site is the location where the incoming aminoacyl-tRNA binds during translation, and by preventing its use, IF1 helps regulate the initiation of protein synthesis.

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  • 14. 

    Which of the following bindings are incorrectly paired up for eukaryotic initiation complex formation?

    • A.

      MRNA > 3' end by PAB

    • B.

      EIF4E > 5' cap of mRNA

    • C.

      EIF4G > eIF4E and PAB

    • D.

      EIF4E > 3' end by PAB

    Correct Answer
    D. EIF4E > 3' end by PAB
  • 15. 

    In order for the eIF protein to scan the 40S ribosomal subunit for  the first AUG it needs helicase activity to resolve the secondary structure in the 5'UTR of the mRNA and does not require ATP for this to take place.

    • A.

      True

    • B.

      False

    Correct Answer
    B. False
    Explanation
    The statement is false because the eIF protein does require ATP for helicase activity to resolve the secondary structure in the 5'UTR of the mRNA. ATP is needed for the energy required to unwind the secondary structure and allow the eIF protein to scan for the first AUG. Without ATP, the eIF protein would not be able to perform this function effectively.

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  • Current Version
  • Mar 21, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Sep 30, 2011
    Quiz Created by
    Michael Kagan
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