Question 1

Which of the following best explains the dark coloration of urine in sample B compared to sample A, as shown in the first image?

Accepted Answer

Sample B is indicative of alkaptonuria, where homogentisic acid accumulates due to a deficiency in homogentisic acid oxidase.

Question 2

According to the one gene-one enzyme hypothesis, which of the following statements is most accurate based on modern understanding?

Accepted Answer

Each gene encodes a single polypeptide, but not all proteins are enzymes.

Question 3

A patient is diagnosed with phenylketonuria (PKU). Which enzyme is most likely deficient, and what is the consequence for phenylalanine metabolism?

Accepted Answer

Phenylalanine hydroxylase; phenylalanine cannot be converted to tyrosine.

Question 4

Which codon serves as the universal start codon for translation in both prokaryotes and eukaryotes?

Accepted Answer

$$\mathrm{AUG}$$

Question 5

The genetic code is described as 'degenerate.' What does this mean?

Accepted Answer

Multiple codons can specify the same amino acid.

Question 6

Which of the following best describes the role of aminoacyl-tRNA synthetases in translation?

Accepted Answer

They attach the correct amino acid to its corresponding tRNA, ensuring fidelity in translation.

Question 7

A mutation changes the third base of a glycine codon from GGU to GGC. What is the likely effect on the protein product?

Accepted Answer

The amino acid sequence will remain unchanged due to the degeneracy of the genetic code.

Question 8

Which ribosomal RNA (rRNA) component is responsible for catalyzing peptide bond formation during translation?

Accepted Answer

23S rRNA

Question 9

In bacteria, what is the function of the Shine-Dalgarno sequence during translation initiation?

Accepted Answer

It aligns the mRNA on the ribosome by base pairing with the 16S rRNA.

Question 10

Which of the following best explains why polar and charged amino acids are often found on the surface of proteins?

Accepted Answer

They are hydrophilic and interact favorably with the aqueous environment.

Question 11

A mutation in the anticodon of a tRNA changes it from $$\mathrm{GAA} to$$ $$\mathrm{GUA}. $$Which mRNA codon will this mutated tRNA now recognize?

Accepted Answer

$$\mathrm{CAU}$$

Question 12

Which of the following statements about translation in prokaryotes is correct?

Accepted Answer

Translation can begin before transcription is complete, a process called coupling.

Question 13

Which of the following is a direct consequence of the wobble hypothesis?

Accepted Answer

A single tRNA can recognize multiple codons for the same amino acid.

Question 14

Which of the following best describes the directionality of a polypeptide chain?

Accepted Answer

It is synthesized from the N-terminal to the C-terminal end.

Question 15

A mutation in a gene results in the production of a nonfunctional enzyme in a metabolic pathway. Which experimental approach, as used by Beadle and Tatum, would help identify the step affected?

Accepted Answer

Supplying the organism with each intermediate in the pathway and observing which one restores growth.

Question 16

Which of the following is NOT a function of tRNA molecules?

Accepted Answer

Catalyzing peptide bond formation.

Question 17

Which of the following best describes the role of release factors in translation termination?

Accepted Answer

They bind to stop codons and promote the release of the polypeptide from the ribosome.

Question 18

Which of the following is true regarding the Kozak sequence in eukaryotic translation?

Accepted Answer

It is a consensus sequence that helps the ribosome identify the correct start codon.

Question 19

Which of the following best explains why the error rate in aminoacyl-tRNA synthetase activity is so low?

Accepted Answer

The enzyme recognizes multiple features of the tRNA, including modified bases, ensuring high specificity.

The Molecular Biology of Translation: From Genes to Proteins

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