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 terminus on the $$\alpha-$$phosphate of the incoming dNTP, forming a phosphodiester bond and releasing pyrophosphate: 
$$	ext{(dNMP)}_{n} + 	ext{dNTP} ightarrow 	ext{(dNMP)}_{n+1} + 	ext{PP}_i$$

Question 2

During eukaryotic DNA replication, what is the significance of 'origins of replication' and how does replication proceed from these sites?

Accepted Answer

Replication begins at several fixed origins and proceeds bidirectionally until replication forks meet

Question 3

Which of the following best describes the role of helicase and topoisomerase during DNA replication?

Accepted Answer

Helicase unwinds double-stranded DNA using ATP, while topoisomerase relieves torsional stress caused by unwinding

Question 4

What is the function of DNA polymerase I during the removal of RNA primers in DNA replication?

Accepted Answer

It removes RNA primers using its 5'→3' exonuclease activity and replaces them with DNA nucleotides

Question 5

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

Accepted Answer

It is synthesized discontinuously as Okazaki fragments in the 5'→3' direction

Question 6

Which of the following is true regarding the three eukaryotic RNA polymerases and their functions?

Accepted Answer

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

Question 7

What is the role of the TATA box in eukaryotic transcription?

Accepted Answer

It is a promoter element that helps position RNA polymerase II at the transcription start site

Question 8

How does histone acetylation affect transcriptional activity in eukaryotic cells?

Accepted Answer

It neutralizes lysine residues, weakening histone-DNA interactions and promoting transcription

Question 9

Which of the following best describes the process and significance of alternative splicing in eukaryotic gene expression?

Accepted Answer

It allows a single gene to produce multiple protein isoforms by varying the combination of exons included in the final mRNA

Question 10

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

Accepted Answer

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

Question 11

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

Accepted Answer

AUG; methionine

Question 12

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

Accepted Answer

It attaches the correct amino acid to its corresponding tRNA using ATP

Question 13

Which of the following statements correctly compares bacterial and eukaryotic ribosomes?

Accepted Answer

Bacterial ribosomes are 70S (50S + 30S), while eukaryotic ribosomes are 80S (60S + 40S)

Question 14

During the elongation stage of translation, what is the sequence of events that occurs at the ribosome?

Accepted Answer

Aminoacyl-tRNA enters the A site, peptide bond forms, ribosome translocates to move the peptidyl-tRNA to the P site

Question 15

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

Accepted Answer

Permanent gene inactivation and gene silencing

Question 16

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 17

Which of the following is a function of the spliceosome in eukaryotic cells?

Accepted Answer

It removes introns from pre-mRNA and joins exons together

Question 18

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

Accepted Answer

DNA methylation at CpG dinucleotides

Question 19

A mutation in the gene encoding DNA methyltransferase 1 (DNMT1) would most likely affect which cellular process?

Accepted Answer

Maintenance of DNA methylation patterns during DNA replication

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

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