Question 1

Which enzyme is responsible for relieving the torsional stress generated during DNA unwinding at the replication fork?

Accepted Answer

Topoisomerase

Question 2

During eukaryotic DNA replication, what is the significance of 'origins' and how do they function?

Accepted Answer

Origins are fixed sites programmed to initiate replication at specific times in S phase.

Question 3

Which of the following best describes the directionality and initiation of eukaryotic DNA replication?

Accepted Answer

Bidirectional from several fixed origins

Question 4

What is the role of DNA polymerase in the formation of a new DNA strand?

Accepted Answer

It catalyzes the nucleophilic attack by the 3'-OH of the primer terminus on the $\alpha$-phosphate of the incoming dNTP, forming a phosphodiester bond and releasing pyrophosphate.

Question 5

Which activities are associated with DNA polymerase I during DNA replication?

Accepted Answer

3'-exonuclease and 5'-exonuclease activities

Question 6

In the removal of RNA primers during DNA replication, which enzyme synthesizes the RNA primer and which enzyme replaces it with DNA?

Accepted Answer

Primase synthesizes the RNA primer; DNA polymerase I replaces it with DNA.

Question 7

Which of the following statements about the lagging strand during DNA replication is correct?

Accepted Answer

It is synthesized discontinuously, forming Okazaki fragments.

Question 8

What is the function of helicase at the replication fork?

Accepted Answer

It catalyzes the ATP-dependent unwinding of double-stranded DNA to form single-stranded DNA.

Question 9

Which of the following is true regarding the TATA box in eukaryotic transcription?

Accepted Answer

It is the eukaryotic counterpart to the bacterial -10 region and is involved in transcription initiation.

Question 10

What is the effect of histone acetylation on transcriptional activity?

Accepted Answer

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

Question 11

Which RNA polymerase is responsible for transcribing protein-coding genes in eukaryotes?

Accepted Answer

RNA polymerase II

Question 12

What is the role of the poly(A) tail added to eukaryotic mRNA during posttranscriptional processing?

Accepted Answer

It increases mRNA stability; the longer the tail, the longer the half-life.

Question 13

Which process allows a single gene to specify multiple proteins in eukaryotes?

Accepted Answer

Alternative splicing

Question 14

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

Accepted Answer

mRNA is read 5' to 3'; polypeptide is synthesized from N- to C-terminus.

Question 15

What is the function of the anticodon loop of tRNA during translation?

Accepted Answer

It contains a trinucleotide sequence complementary to the codon in mRNA.

Question 16

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

Accepted Answer

AUG; methionine

Question 17

What is the composition of the eukaryotic ribosome in terms of its subunits?

Accepted Answer

80S ribosome composed of 60S and 40S subunits

Question 18

During bacterial translation initiation, what is the correct sequence of events involving ribosomal subunits?

Accepted Answer

The 30S subunit binds to the mRNA, then the 50S subunit joins to form the 70S initiation complex.

Question 19

Which DNA methyltransferase is primarily responsible for maintenance of methylation patterns in mammalian cells?

Accepted Answer

Dnmt1

Question 20

Which epigenetic process is responsible for X chromosome inactivation and gene imprinting in mammals?

Accepted Answer

DNA methylation

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

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