Question 1

Which of the following best describes a missense mutation?

Accepted Answer

A mutation that results in a change in the primary sequence of a polypeptide by substituting one amino acid for another.

Question 2

A single base pair substitution in the gene encoding the β hemoglobin polypeptide causes sickle cell anemia. Using the genetic code, what amino acid change occurs in this disease?

Accepted Answer

Glutamic acid (Glu) is replaced by valine (Val).

Question 3

Which of the following mutations is most likely to result in a completely non-functional protein?

Accepted Answer

A frameshift mutation near the beginning of the gene.

Question 4

If a DNA sequence 5'-ATGAAGTTTGGCTAA-3' is mutated to 5'-ATGAAGTTTAGCTAA-3', what type of mutation has occurred?

Accepted Answer

Missense mutation

Question 5

Which of the following best explains why a silent mutation might still affect the efficiency of translation?

Accepted Answer

It changes the codon to one that is less preferred by the cell, possibly slowing translation.

Question 6

A mutation changes the DNA sequence 3'-TACTTCAAACCGATT-5' to 3'-TACATCAAACCGATT-5'. What is the effect on the resulting protein?

Accepted Answer

A nonsense mutation occurs, introducing a premature stop codon.

Question 7

Which of the following statements about alleles is correct?

Accepted Answer

Alleles are alternative versions of a gene that may produce different traits.

Question 8

In the context of gene regulation in prokaryotes, what is the function of the operator in an operon?

Accepted Answer

It is the DNA sequence where a repressor protein can bind to regulate transcription.

Question 9

A bacterial cell is growing in a medium that contains all amino acids, sugars, and vitamins. Which of the following is most likely to occur regarding gene expression?

Accepted Answer

The cell will downregulate genes for biosynthetic enzymes and upregulate transporter proteins.

Question 10

Which of the following best describes the effect of a frameshift mutation caused by the insertion of a single nucleotide near the start of a gene?

Accepted Answer

It will likely result in a non-functional protein due to extensive missense and/or premature stop codons.

Question 11

Which of the following is an example of an induced mutation?

Accepted Answer

A mutation caused by exposure to X-rays.

Question 12

In the trp operon of E. coli, what happens when tryptophan is present in the environment?

Accepted Answer

Tryptophan binds to the trp repressor, activating it, and the operon is turned off.

Question 13

A mutation deletes three nucleotides from the middle of a gene. What is the most likely result?

Accepted Answer

A single amino acid is deleted, but the reading frame is preserved.

Question 14

Which of the following best describes a neutral mutation?

Accepted Answer

A mutation that does not change the phenotype of the organism.

Question 15

Which of the following is true about the trp repressor protein in E. coli?

Accepted Answer

It is always produced, but only active when bound to tryptophan.

Question 16

Which of the following best explains why carcinogens are considered mutagens?

Accepted Answer

They are chemicals or agents that increase the rate of mutations, some of which can lead to cancer.

Question 17

A prokaryotic gene cluster that is transcribed as a single mRNA and encodes multiple proteins is called:

Accepted Answer

A polycistronic operon.

Question 18

Which of the following is the correct sequence of events for the regulation of the trp operon when tryptophan is absent?

Accepted Answer

Repressor is inactive, RNA polymerase transcribes the operon, enzymes for tryptophan synthesis are produced.

Question 19

Which of the following best describes a base-pair substitution mutation?

Accepted Answer

A mutation that replaces one nucleotide and its partner with another pair.

LEC 23: Mutations and Gene Regulation in Prokaryotes

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