Question 1

Which enzyme is responsible for catalyzing the formation of a phosphodiester bond during DNA replication, and what is the chemical reaction involved?

Accepted Answer

DNA polymerase; catalyzes the nucleophilic attack by the 3'-OH of the primer on the $$\alpha-$$phosphate of the incoming dNTP, forming a phosphodiester bond and releasing pyrophosphate: $$	ext{(dNMP)}_{n} + 	ext{dNTP} ightarrow 	ext{(dNMP)}_{n+1} + PP_i$$

Question 2

During eukaryotic DNA replication, what is the significance of multiple origins of replication on linear chromosomes?

Accepted Answer

They enable bidirectional replication from several fixed origins, allowing the entire chromosome to be replicated efficiently during S phase.

Question 3

What is the role of topoisomerase during DNA replication?

Accepted Answer

It relieves torsional stress caused by helicase-mediated unwinding of DNA by introducing transient breaks in the DNA backbone.

Question 4

Which of the following best describes the function of primase during DNA replication?

Accepted Answer

It synthesizes short RNA primers that provide a 3'-OH group for DNA polymerase to initiate DNA synthesis.

Question 5

In the context of eukaryotic transcription, what is the primary function of the TATA box?

Accepted Answer

It serves as the eukaryotic counterpart to the bacterial -10 region, functioning as a core promoter element for transcription initiation.

Question 6

Which of the following statements about the three eukaryotic RNA polymerases is correct?

Accepted Answer

RNA polymerase III transcribes small RNA genes, such as tRNA and 5S rRNA.

Question 7

What is the effect of histone acetylation on transcriptional activity in eukaryotic cells?

Accepted Answer

It neutralizes basic lysine residues, weakening histone-DNA interactions and promoting high transcriptional activity.

Question 8

Which of the following best describes the process and significance of alternative splicing in eukaryotes?

Accepted Answer

It allows a single gene to specify multiple proteins by varying the combination of exons included in the final mRNA.

Question 9

During translation, what is the direction in which mRNA is read and the polypeptide is synthesized?

Accepted Answer

mRNA is read 5' to 3', and the polypeptide is synthesized from the N- to C-terminus.

Question 10

Which codon serves as the start codon in eukaryotic translation, and what amino acid does it encode?

Accepted Answer

AUG; encodes methionine

Question 11

What is the function of aminoacyl-tRNA synthetase during translation?

Accepted Answer

It attaches the correct amino acid to its corresponding tRNA, forming aminoacyl-tRNA.

Question 12

Which of the following statements about the ribosome is correct?

Accepted Answer

The bacterial ribosome is 70S, composed of 50S and 30S subunits.

Question 13

What is the role of the A, P, and E sites on the ribosome during translation?

Accepted Answer

A site binds aminoacyl-tRNA, P site holds the peptidyl-tRNA, E site is the exit site for deacylated tRNA.

Question 14

Which of the following best describes the process of nick translation during DNA replication?

Accepted Answer

DNA polymerase I uses its 5' to 3' exonuclease activity to remove RNA primers and its polymerase activity to replace them with deoxynucleotides.

Question 15

Which of the following is a direct consequence of DNA methylation at CpG islands in eukaryotic cells?

Accepted Answer

Permanent gene inactivation, such as X chromosome inactivation or gene imprinting.

Question 16

A mutation in a gene encoding a DNA methyltransferase (DNMT1) would most likely affect which process?

Accepted Answer

Maintenance of DNA methylation patterns during DNA replication.

Question 17

Which of the following events occurs during the termination of transcription in eukaryotes?

Accepted Answer

The pre-mRNA is cleaved 11 to 30 nucleotides downstream of the AAUAAA signal, and a poly(A) tail is added by poly(A) polymerase.

Question 18

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

Accepted Answer

The lagging strand is synthesized discontinuously because DNA polymerase can only add nucleotides to the 3' end, resulting in short fragments that are later joined.

DNA Replication, Transcription, and Translation: Core Mechanisms in Biochemistry

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