Question 1

Which of the following statements best describes the central dogma of molecular genetics as formulated by Francis Crick?

Accepted Answer

DNA is transcribed into RNA, which is then translated into protein.

Question 2

A codon is defined as:

Accepted Answer

A sequence of three nucleotides in mRNA that specifies an amino acid or stop signal.

Question 3

Which of the following codons is the universal start codon in both bacteria and eukaryotes?

Accepted Answer

$$\mathrm{AUG}$$

Question 4

In bacteria, the initiator tRNA carries which modified amino acid?

Accepted Answer

N-formylmethionine (fMet)

Question 5

Which of the following is NOT a characteristic of the genetic code?

Accepted Answer

It is ambiguous, so one codon can code for multiple amino acids.

Question 6

The wobble hypothesis explains how:

Accepted Answer

A single tRNA can recognize multiple codons due to flexible base pairing at the third codon position.

Question 7

Which site on the ribosome is responsible for holding the tRNA carrying the growing polypeptide chain?

Accepted Answer

P (peptidyl) site

Question 8

During bacterial translation initiation, the Shine-Dalgarno sequence is important because:

Accepted Answer

It binds to the 16S rRNA of the small ribosomal subunit to position the ribosome correctly on the mRNA.

Question 9

A nonsense suppressor mutation can result in:

Accepted Answer

A stop codon being read as a sense codon, allowing translation to continue.

Question 10

Which of the following posttranslational modifications is responsible for targeting proteins for degradation in the proteasome?

Accepted Answer

Ubiquitination

Question 11

A mutation introduces a premature termination codon (PTC) in an mRNA. What is the likely cellular response?

Accepted Answer

The mRNA will be degraded by nonsense-mediated decay (NMD).

Question 12

Which of the following best describes the function of aminoacyl-tRNA synthetases?

Accepted Answer

They attach the correct amino acid to its corresponding tRNA.

Question 13

In eukaryotic translation initiation, which sequence context around the start codon is most favorable according to Kozak’s rules?

Accepted Answer

A guanine at the +4 position and a purine (preferably adenine) at the -3 position

Question 14

Which of the following is a real-world example of a human disease caused by nonsense-mediated decay due to a premature stop codon?

Accepted Answer

Cystic fibrosis

Question 15

If a tRNA has the anticodon 5'-GAA-3', which mRNA codon will it recognize, and which amino acid will it carry?

Accepted Answer

5'-CUU-3', carrying Leucine

Question 16

Which of the following equations correctly represents the formation of a peptide bond during translation?

Accepted Answer

$$\mathrm{Amino\ acid}_1 + \mathrm{Amino\ acid}_2 \rightarrow \mathrm{Dipeptide} + H_2O$$

Question 17

Which of the following statements about open reading frames (ORFs) is correct?

Accepted Answer

ORFs are composed of a contiguous, non-overlapping string of codons that code for a protein.

Question 18

Which of the following is a function of posttranslational modifications?

Accepted Answer

To ensure that proteins are directed to their correct cellular compartments.

Question 19

A mutation changes a codon from UAU (tyrosine) to UAA. What is the most likely effect on the resulting protein?

Accepted Answer

The protein will be truncated due to the introduction of a stop codon.

Translation of mRNA: The Genetic Code and Protein Synthesis

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