Q: If a DNA template strand sequence is $$\text{TAC}$$, what is the corresponding mRNA codon and which amino acid does it code for?

mRNA codon: $$\text{AUG}$$; amino acid: Methionine

Question 1

Which type of mutation is responsible for sickle-cell disease, as shown in the provided diagram, and what is its effect on the protein product?

Accepted Answer

A missense mutation caused by a single nucleotide-pair substitution, resulting in valine replacing glutamic acid.

Question 2

A nucleotide-pair insertion or deletion that is not a multiple of three is most likely to cause which of the following effects?

Accepted Answer

A frameshift mutation, altering the reading frame and causing extensive missense and usually a premature stop codon.

Question 3

In the context of neonatal diabetes, doctors compare a patient’s insulin cDNA sequence to the wild-type sequence. If a codon changes from $$	ext{GAA} to$$ $$	ext{GAG}$$, what type of mutation is this and what is its effect?

Accepted Answer

Silent mutation; no change in the amino acid sequence.

Question 4

Which of the following best describes a nonsense mutation?

Accepted Answer

A mutation that changes a codon for an amino acid into a stop codon, causing premature termination of translation.

Question 5

A patient’s insulin gene has a nucleotide-pair substitution that changes a codon from $$	ext{UAC} ($$tyrosine) to $$	ext{UAA} ($$stop). What is the consequence of this mutation?

Accepted Answer

The protein will be truncated and likely nonfunctional due to premature termination.

Question 6

Which of the following statements about mutagens is correct?

Accepted Answer

Mutagens can be physical (like UV light) or chemical (like nucleotide analogs), and most mutagens are carcinogenic.

Question 7

If a DNA template strand sequence is $$	ext{TAC}$$, what is the corresponding mRNA codon and which amino acid does it code for?

Accepted Answer

mRNA codon: $$	ext{AUG}$$; amino acid: Methionine

Question 8

Which of the following best explains why some nucleotide-pair substitutions have no effect on the encoded protein?

Accepted Answer

The genetic code is redundant, so multiple codons can code for the same amino acid.

Question 9

A frameshift mutation occurs near the end of a gene. What is the likely outcome for the protein product?

Accepted Answer

The protein may retain partial function if the frameshift is near the end and does not disrupt critical regions.

Question 10

Which of the following is a real-world example of a missense mutation causing a phenotype change?

Accepted Answer

A mutation in the tyrosinase gene causing albinism in the Asinara donkey.

Question 11

Which equation best represents the probability of a spontaneous mutation during DNA replication, given the rate is about one nucleotide in every $$10^9$$ nucleotides?

Accepted Answer

Probability $$= \frac{1}{10^9$}$$

Question 12

Which of the following best describes the definition of a gene according to modern molecular biology?

Accepted Answer

A gene is a region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule.

Question 13

A patient with neonatal diabetes has a nucleotide-pair substitution in the insulin gene. Which step would a medical geneticist take to determine the effect of this mutation?

Accepted Answer

Compare the patient’s cDNA sequence to the wild-type, identify the changed codon, and use a codon table to determine the amino acid change.

Question 14

Which of the following is NOT a possible outcome of a nucleotide-pair substitution mutation?

Accepted Answer

Frameshift mutation

Question 15

If a chemical mutagen inserts itself into DNA and distorts the double helix, what is the most likely result?

Accepted Answer

Incorrect DNA replication, leading to mutations such as insertions or deletions.

Question 16

Which of the following best explains why mutations are important in evolution?

Accepted Answer

Mutations provide the raw material (new alleles) on which natural selection acts.

Question 17

A DNA sequence is mutated from $$	ext{GAG} to$$ $$	ext{GTG} in $$the coding region. What is the effect on the protein, and which disease is associated with this mutation?

Accepted Answer

The protein will have valine instead of glutamic acid, causing sickle-cell disease.

Question 18

Which of the following is a characteristic of a silent mutation?

Accepted Answer

The mutation does not change the amino acid sequence due to redundancy in the genetic code.

Question 19

Which of the following best describes the effect of a frameshift mutation caused by the insertion of two nucleotides in the middle of a gene?

Accepted Answer

All codons downstream of the insertion will be improperly grouped, resulting in extensive missense mutations and usually a premature stop codon.

Mutations: Effects on Protein Structure and Function

Study Guide - Practice Questions

Study Guide - Flashcards