Question 1

Which of the following statements best describes the difference between purines and pyrimidines in nucleic acids?

Accepted Answer

Purines include adenine and guanine, while pyrimidines include thymine, cytosine, and uracil.

Question 2

During DNA replication, which enzyme is responsible for joining Okazaki fragments on the lagging strand?

Accepted Answer

DNA ligase

Question 3

If a segment of DNA has the sequence 5'-ATGCCGTA-3', what would be the complementary RNA sequence produced during transcription?

Accepted Answer

3'-UACGGCAU-5'

Question 4

Which of the following best explains why DNA replication is described as 'semiconservative'?

Accepted Answer

Each daughter DNA molecule consists of one parental strand and one newly synthesized strand.

Question 5

A mutation changes the codon UAU (tyrosine) to UAA. What type of mutation is this, and what is its likely effect?

Accepted Answer

Nonsense mutation; the protein will be prematurely terminated.

Question 6

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

Accepted Answer

mRNA processing (capping, tailing, and splicing)

Question 7

What is the function of the promoter region in a gene?

Accepted Answer

It is the binding site for RNA polymerase to initiate transcription.

Question 8

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 mRNA codon using its anticodon.

Question 9

A researcher is using PCR to amplify a DNA sequence. Which of the following steps is NOT part of a typical PCR cycle?

Accepted Answer

Translation of mRNA into protein

Question 10

Which of the following statements about the genetic code is TRUE?

Accepted Answer

The genetic code is universal and shared by almost all organisms.

Question 11

Which of the following best explains why a frameshift mutation is often more damaging than a point mutation?

Accepted Answer

Frameshift mutations change the reading frame, altering every amino acid downstream of the mutation.

Question 12

In the lac operon, what happens when lactose is present in the environment?

Accepted Answer

Lactose binds to the repressor, causing it to detach from the operator and allowing transcription.

Question 13

Which of the following modifications to histones would most likely increase gene expression?

Accepted Answer

Addition of acetyl groups (acetylation)

Question 14

A woman is a genetic mosaic for X-linked traits. What is the molecular basis for this phenomenon?

Accepted Answer

One X chromosome is randomly inactivated in each cell during early embryonic development.

Question 15

Which of the following is a direct result of alternative RNA splicing in eukaryotes?

Accepted Answer

Production of different polypeptides from the same gene

Question 16

A mutation in the ras gene leads to continuous cell division. What type of gene is ras, and what is the consequence of its mutation?

Accepted Answer

Proto-oncogene; mutation converts it to an oncogene, promoting cancer

Question 17

Which of the following best describes the role of gel electrophoresis in DNA analysis?

Accepted Answer

It separates DNA fragments based on size and charge.

Question 18

Which of the following is a key feature of the polymerase chain reaction (PCR) that allows it to amplify DNA from ancient or degraded samples?

Accepted Answer

It requires only a small amount of starting DNA.

Question 19

Which of the following best explains why the genetic code is considered redundant but not ambiguous?

Accepted Answer

More than one codon can code for the same amino acid, but each codon specifies only one amino acid.

Molecular Biology: DNA Structure, Replication, and Gene Expression

Study Guide - Practice Questions