Question 1

Which of the following best describes the anatomy of a structural gene in eukaryotes?

Accepted Answer

A promoter, regulatory sequence, transcribed region, and terminator.

Question 2

A patient is diagnosed with a genetic disorder caused by a mutation that introduces a premature stop codon in the middle of a gene. Which type of mutation is most likely responsible, and what is the expected effect on the protein?

Accepted Answer

Nonsense mutation; the protein will be truncated and likely nonfunctional.

Question 3

During mRNA processing in eukaryotes, which of the following modifications occurs at the 5' end of the pre-mRNA, and what is its function?

Accepted Answer

Addition of a 7-methylguanosine cap; it protects mRNA from degradation and aids in ribosome binding.

Question 4

A DNA coding strand has the sequence 5'-ATG GAA TGA-3'. What is the corresponding mRNA sequence and the resulting amino acid sequence?

Accepted Answer

mRNA: 5'-AUG GAA UGA-3'; Amino acids: Met-Glu-Stop

Question 5

Which of the following statements correctly compares transcription and translation in prokaryotes and eukaryotes?

Accepted Answer

In prokaryotes, transcription and translation are coupled in the cytoplasm; in eukaryotes, transcription occurs in the nucleus and translation in the cytosol.

Question 6

A patient’s mRNA transcript is found to be longer than normal due to the inclusion of an intron. Which RNA processing error most likely occurred, and what is a possible consequence?

Accepted Answer

Splicing error; the resulting protein may be nonfunctional due to a frameshift or premature stop codon.

Question 7

A mutation in the BRCA1 gene changes the codon GAA to GAG. Both codons code for glutamic acid. What type of mutation is this, and what is the expected effect on the protein?

Accepted Answer

Silent mutation; no change in the protein sequence.

Question 8

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

Accepted Answer

It acts as an adaptor, matching its anticodon to the mRNA codon and carrying the corresponding amino acid.

Question 9

A patient with thalassemia is found to have an abnormal mRNA transcript that is shorter than normal. Gel electrophoresis shows a smaller band compared to the control. What is the most likely explanation?

Accepted Answer

Exon skipping due to a splicing mutation, resulting in a shorter mRNA and truncated protein.

Question 10

Which of the following equations correctly represents the directionality of mRNA synthesis during transcription?

Accepted Answer

$$5' \rightarrow 3'$$

Question 11

A gene editing experiment uses CRISPR-Cas9 to introduce a double-strand break at a specific locus. If the cell repairs the break using non-homologous end joining (NHEJ), what is the most likely outcome?

Accepted Answer

Small insertions or deletions (indels) at the break site, potentially disrupting gene function.

Question 12

A DNA template strand has the sequence 3'-TAC GGA TTT-5'. What is the mRNA sequence produced during transcription?

Accepted Answer

5'-AUG CCU AAA-3'

Question 13

A patient’s gene has a deletion of two nucleotides in the coding region. What is the most likely effect on the resulting protein?

Accepted Answer

A frameshift mutation, altering the reading frame and likely producing a nonfunctional protein.

Question 14

Which of the following best explains why a frameshift mutation is often more severe than a missense mutation?

Accepted Answer

A frameshift alters the reading frame, changing all downstream amino acids and often introducing a premature stop codon.

Question 15

Which of the following is a function of the poly-A tail added during mRNA processing in eukaryotes?

Accepted Answer

It increases mRNA stability and lifespan in the cytosol.

Question 16

A mutation in the splice donor site of an intron leads to the use of a cryptic splice site within the intron. What is the most likely result in the mature mRNA and protein product?

Accepted Answer

Inclusion of intronic sequence in the mRNA, potentially causing a frameshift and nonfunctional protein.

Question 17

Which of the following best describes the role of the PAM sequence in CRISPR-Cas9 gene editing?

Accepted Answer

It is required for Cas9 to recognize and bind the target DNA sequence.

Question 18

A patient’s DNA sequence is found to have a three-nucleotide deletion in the coding region of a gene. What is the most likely effect on the protein product?

Accepted Answer

An in-frame deletion, resulting in the loss of one amino acid but preserving the reading frame.

Question 19

Which of the following best summarizes the central dogma of molecular biology?

Accepted Answer

DNA is transcribed to RNA, which is translated to protein.

Question 20

A researcher introduces a mutation in the coding region of a gene that changes a codon from UAU (tyrosine) to UGU (cysteine). What type of mutation is this, and what is the possible effect?

Accepted Answer

Missense mutation; the protein may have altered function depending on the role of the amino acid.

Central Dogma, Gene Expression, Mutations, and CRISPR-Cas9: Study Guide for Genetics

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