Question 1

Which of the following statements best explains why the genetic code is described as 'redundant but not ambiguous'?

Accepted Answer

More than one codon can specify the same amino acid, but no codon specifies more than one amino acid.

Question 2

A mutation changes the DNA sequence from 5'-TAC-3' to 5'-TAA-3'. What type of mutation is this, and what is the likely effect on the resulting protein?

Accepted Answer

Nonsense mutation; translation will terminate prematurely, likely producing a nonfunctional protein.

Question 3

During eukaryotic gene expression, which of the following modifications occurs to the pre-mRNA before it leaves the nucleus?

Accepted Answer

Addition of a 5' cap and a poly-A tail, and removal of introns.

Question 4

Which of the following best describes the role of tRNA during translation?

Accepted Answer

tRNA carries amino acids to the ribosome and matches them to the coded mRNA message via its anticodon.

Question 5

In bacteria, why can translation of mRNA begin before transcription has finished, but not in eukaryotes?

Accepted Answer

Bacteria lack a nuclear envelope, allowing ribosomes to access mRNA as it is being transcribed.

Question 6

A researcher observes that a single nucleotide insertion in a gene leads to a completely different and nonfunctional protein. What is the most likely explanation for this observation?

Accepted Answer

The insertion caused a frameshift mutation, altering the reading frame.

Question 7

Which of the following sequences represents a start codon in mRNA, and what amino acid does it code for?

Accepted Answer

$$\mathrm{AUG}$$; Methionine

Question 8

Which of the following best describes the function of the poly-A tail added to eukaryotic mRNA?

Accepted Answer

It facilitates export of mRNA from the nucleus, protects mRNA from degradation, and assists in ribosome binding.

Question 9

Which site on the ribosome does the charged tRNA first enter during elongation of translation?

Accepted Answer

A site

Question 10

A patient is diagnosed with sickle-cell disease, which is caused by a single nucleotide substitution in the hemoglobin gene. What type of mutation is this, and what is its effect?

Accepted Answer

Missense mutation; one amino acid is changed, altering protein function.

Question 11

Which of the following statements about RNA polymerase is correct?

Accepted Answer

RNA polymerase binds to the promoter region to initiate transcription.

Question 12

Which of the following best explains why a silent mutation does not affect the protein sequence?

Accepted Answer

The mutation changes a codon to one that codes for the same amino acid due to redundancy in the genetic code.

Question 13

During translation, what is the role of the release factor when a stop codon is reached?

Accepted Answer

It adds a water molecule to the polypeptide, causing its release from the ribosome.

Question 14

Which of the following is a direct consequence of a frameshift mutation caused by a nucleotide deletion?

Accepted Answer

All codons downstream of the mutation are changed, potentially altering every amino acid after the mutation.

Question 15

Which of the following processes occurs in the nucleus of eukaryotic cells but not in prokaryotic cells?

Accepted Answer

RNA processing (capping, polyadenylation, and splicing)

Question 16

A scientist observes that multiple ribosomes are attached to a single mRNA molecule in a eukaryotic cell. What is the term for this structure, and what is its significance?

Accepted Answer

Polyribosome (polysome); it allows for simultaneous synthesis of multiple copies of a protein from one mRNA.

Question 17

Which of the following best describes the sequence of events during the elongation phase of translation?

Accepted Answer

A charged tRNA enters the A site, peptide bond forms, tRNA in P site moves to E site and exits.

Question 18

Which of the following is NOT a possible post-translational modification of a protein?

Accepted Answer

Splicing of introns from mRNA

Question 19

If the DNA template strand reads 3'-TACGGT-5', what is the sequence of the mRNA produced during transcription?

Accepted Answer

5'-AUGCCA-3'

Question 20

Which of the following best explains why energy in the form of GTP is required during translation?

Accepted Answer

GTP provides energy for the movement of the ribosome along the mRNA and for the binding of tRNA to the ribosome.

Gene Expression: From Gene to Protein (Chapter 14 Study Notes)

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