Question 1

Which of the following statements best explains why DNA polymerase can only add nucleotides to the 3' end of a growing DNA strand during replication?

Accepted Answer

The 3' end contains a free hydroxyl group ($$-OH) $$required for the formation of a phosphodiester bond with the incoming nucleotide.

Question 2

A scientist isolates a nucleic acid and determines that it contains the sugar ribose, uracil as a base, and is single-stranded. Which type of molecule has the scientist most likely isolated?

Accepted Answer

RNA

Question 3

Which of the following best describes the role of telomerase in eukaryotic cells?

Accepted Answer

It extends the 3' end of the parental DNA strand to prevent chromosome shortening during replication.

Question 4

During DNA replication, which enzyme is responsible for relieving the tension created ahead of the replication fork by unwinding?

Accepted Answer

Topoisomerase

Question 5

A mutation changes a DNA codon from $$	ext{GAA} to$$ $$	ext{GAG}. $$Both codons code for glutamic acid. What type of mutation is this?

Accepted Answer

Silent mutation

Question 6

Which of the following best explains why the addition of nucleotides during DNA replication is overall exergonic, even though the formation of a phosphodiester bond is endergonic?

Accepted Answer

The hydrolysis of two phosphate groups from the incoming dNTP releases energy that drives the reaction.

Question 7

Which of the following statements about the lac operon in E. coli is correct?

Accepted Answer

Allolactose acts as an inducer by binding to the repressor, causing it to release from the operator and allowing transcription.

Question 8

Which of the following best describes the difference between a purine and a pyrimidine?

Accepted Answer

Purines have a double-ring structure, while pyrimidines have a single-ring structure.

Question 9

A DNA sequence is mutated by the insertion of a single nucleotide. What is the most likely consequence of this mutation?

Accepted Answer

It causes a frameshift mutation, altering the reading frame of the gene.

Question 10

Which of the following is true regarding the process of transcription in eukaryotes?

Accepted Answer

Transcription factors are required for RNA polymerase to bind to the promoter.

Question 11

Which of the following best describes the function of aminoacyl tRNA synthetase?

Accepted Answer

It attaches the correct amino acid to its corresponding tRNA.

Question 12

In the context of gene regulation, what is the effect of DNA methylation on gene expression?

Accepted Answer

It generally decreases gene expression by making DNA less accessible to transcription factors.

Question 13

Which of the following is a key difference between the trp operon and the lac operon in bacteria?

Accepted Answer

The trp operon is repressible and turned off by its end product, while the lac operon is inducible and turned on by its substrate.

Question 14

Which of the following best describes the structure of a nucleosome?

Accepted Answer

DNA wrapped around a core of histone proteins

Question 15

A researcher observes that a eukaryotic gene produces multiple different proteins from the same pre-mRNA transcript. Which process is responsible for this phenomenon?

Accepted Answer

Alternative RNA splicing

Question 16

Which of the following events occurs at the A site of the ribosome during translation?

Accepted Answer

A charged tRNA carrying the next amino acid binds to the mRNA codon.

Question 17

Which of the following best explains why Okazaki fragments are formed during DNA replication?

Accepted Answer

DNA polymerase can only synthesize DNA in the 5' to 3' direction, so the lagging strand is synthesized discontinuously.

Question 18

Which of the following is a function of the 5' cap added to eukaryotic mRNA during processing?

Accepted Answer

It protects the mRNA from degradation and assists in ribosome binding during translation.

Question 19

Which of the following best describes the role of an operator in a bacterial operon?

Accepted Answer

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

Molecular Genetics and Regulation of Gene Expression: Study Guide

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