Q: Which of the following equations correctly represents the first step in charging a tRNA with its amino acid?

$$\text{Amino acid} + \text{ATP} \rightarrow \text{Aminoacyl-AMP} + \text{PP}_i$$

Question 1

Which of the following statements best explains why the genetic code is described as 'degenerate'?

Accepted Answer

Most amino acids are specified by more than one codon.

Question 2

A mutation causes a single nucleotide insertion in the coding region of a gene. What is the most likely consequence at the protein level?

Accepted Answer

The reading frame will shift, altering all downstream amino acids and possibly introducing an early stop codon.

Question 3

In the classic Nirenberg and Matthaei experiment, poly-U RNA was added to a cell-free translation system. Which polypeptide was produced, and what did this demonstrate?

Accepted Answer

A polypeptide of only phenylalanine, showing UUU codes for Phe.

Question 4

Which feature of the genetic code allows a single tRNA to recognize multiple codons for the same amino acid?

Accepted Answer

Wobble at the third base of the codon.

Question 5

Given the mRNA sequence 5'-AUGGCCUAA-3', what is the resulting polypeptide sequence?

Accepted Answer

Met-Ala

Question 6

A synthetic RNA with the repeating sequence 5'-UCUCUCUC...-3' is translated in vitro. Which of the following best describes the possible polypeptides produced, considering all reading frames?

Accepted Answer

Alternating serine and leucine residues, depending on the reading frame.

Question 7

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

Accepted Answer

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

Question 8

Which of the following is a key difference between translation initiation in prokaryotes and eukaryotes?

Accepted Answer

Prokaryotes use a Shine-Dalgarno sequence to position the ribosome, while eukaryotes use a 5' cap and Kozak sequence.

Question 9

Which of the following best explains why translation and transcription can be coupled in prokaryotes but not in eukaryotes?

Accepted Answer

Prokaryotes do not have a nuclear envelope, so ribosomes can access mRNA as it is being transcribed.

Question 10

A tRNA has the anticodon 5'-GAA-3'. Which mRNA codon will it recognize, and which amino acid will it carry (use the standard genetic code)?

Accepted Answer

5'-CUU-3'; Leucine

Question 11

Which of the following best describes the role of the ribosomal A site during translation?

Accepted Answer

It is where the aminoacyl-tRNA enters and base-pairs with the codon.

Question 12

Which of the following equations correctly represents the first step in charging a tRNA with its amino acid?

Accepted Answer

$$	ext{Amino acid} + 	ext{ATP} ightarrow 	ext{Aminoacyl-AMP} + 	ext{PP}_i$$

Question 13

A DNA coding strand has the sequence 5'-ATG TTT GGC TAA-3'. What is the sequence of the mRNA transcribed from this region (include polarity)?

Accepted Answer

5'-AUG UUU GGC UAA-3'

Question 14

Which of the following statements about the universality of the genetic code is correct?

Accepted Answer

The genetic code is nearly universal, but some exceptions exist in mitochondria and a few microbes.

Question 15

During translation in prokaryotes, which factor is responsible for bringing the initiator tRNA to the ribosome?

Accepted Answer

IF2 (a GTPase)

Question 16

Which of the following best describes the directionality of mRNA translation and polypeptide synthesis?

Accepted Answer

mRNA is read 5'→3', and the protein grows N-terminus→C-terminus.

Question 17

A patient has a mutation in a gene encoding a tRNA synthetase, causing it to attach the wrong amino acid to a tRNA. What is the most likely consequence?

Accepted Answer

The wrong amino acid will be incorporated at codons recognized by that tRNA, potentially altering protein function.

Question 18

Which of the following best describes the role of rRNA in the ribosome?

Accepted Answer

It catalyzes peptide bond formation and helps position tRNAs during translation.

Question 19

Which of the following is a key difference between prokaryotic and eukaryotic mRNAs?

Accepted Answer

Eukaryotic mRNAs are usually monocistronic, while prokaryotic mRNAs are often polycistronic.

The Genetic Code and Translation: Structure, Function, and Mechanisms

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