Question 1

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 product?

Accepted Answer

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

Question 2

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

Accepted Answer

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

Question 3

A researcher is analyzing a gene with the following structure: promoter, regulatory sequence, transcribed region, and terminator. Which component is directly responsible for determining when and how much of the gene product is made?

Accepted Answer

Regulatory sequence

Question 4

Given the DNA coding strand 5'-ATG GAA TGC TAA-3', what is the corresponding mRNA sequence and the resulting amino acid sequence? (Use the genetic code: AUG = Met, GAA = Glu, UGC = Cys, UAA = Stop)

Accepted Answer

mRNA: 5'-AUG GAA UGC UAA-3'; Amino acids: Met-Glu-Cys-Stop

Question 5

Which of the following best describes the difference between pre-mRNA and mature mRNA in eukaryotic cells?

Accepted Answer

Pre-mRNA contains both introns and exons and lacks a 5' cap and poly-A tail; mature mRNA contains only exons and has both a 5' cap and a poly-A tail.

Question 6

A patient with thalassemia is found to have an abnormal mRNA transcript that is shorter than normal when analyzed by gel electrophoresis. Which of the following is the most likely explanation?

Accepted Answer

Exon skipping due to a splicing mutation.

Question 7

In eukaryotic cells, where do transcription and translation occur, respectively?

Accepted Answer

Transcription in the nucleus; translation in the cytosol.

Question 8

A DNA template strand has the sequence 3'-TAC GGT CCA TAA-5'. What is the sequence of the mRNA produced during transcription?

Accepted Answer

5'-AUG CCA GGU UAA-3'

Question 9

Which of the following best explains why frameshift mutations are often more severe than missense mutations?

Accepted Answer

Frameshift mutations alter the reading frame, changing all downstream amino acids and often introducing premature stop codons.

Question 10

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

Accepted Answer

Introduction of small insertions or deletions (indels) that may inactivate the gene.

Question 11

A mutation in the BRCA1 gene changes the codon GAA (glutamic acid) to UAA (stop codon) in the mRNA. What type of mutation is this, and what is the likely effect on the protein?

Accepted Answer

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

Question 12

Which of the following statements about tRNA is correct?

Accepted Answer

tRNA contains an anticodon that pairs with the mRNA codon and an amino acid attachment site.

Question 13

A patient’s gene sequence is found to have a three-nucleotide deletion that removes a single amino acid from the middle of the encoded protein. What type of mutation is this, and what is the likely effect on the reading frame?

Accepted Answer

In-frame deletion; the reading frame is preserved.

Question 14

Which of the following best describes the function of the A site in the ribosome during translation?

Accepted Answer

It is where incoming aminoacyl-tRNAs bind to the ribosome.

Question 15

A mutation in a gene’s splice site causes the inclusion of intronic sequences in the mature mRNA. What is the most likely consequence for the resulting protein?

Accepted Answer

The protein may have extra amino acids or a premature stop codon, leading to loss of function.

Question 16

Which of the following is true regarding the directionality of nucleic acid synthesis during transcription and translation?

Accepted Answer

mRNA is synthesized in the 5' to 3' direction; polypeptides are synthesized from the N-terminus to the C-terminus.

Question 17

A patient with a rare genetic disorder is found to have a mutation in the PAM sequence adjacent to a CRISPR-Cas9 target site. What is the most likely effect on gene editing efficiency?

Accepted Answer

Cas9 will not recognize or cut the DNA at the target site.

Question 18

A mutation in the coding region of a gene changes the codon from AAA (lysine) to AGA (arginine). What type of mutation is this, and what is the potential impact on protein function?

Accepted Answer

Missense mutation; possible change in protein function depending on the role of the amino acid.

Question 19

Which of the following best describes the role of the release factor during translation termination?

Accepted Answer

It binds to the stop codon in the A site and promotes release of the polypeptide from the tRNA in the P site.

Question 20

A patient’s mRNA is found to lack a poly-A tail. Which of the following is the most likely consequence for the mRNA molecule?

Accepted Answer

It will be rapidly degraded in the cytosol, reducing protein synthesis.

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

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