Question 1

Which of the following best describes the structural difference between purines and pyrimidines?

Accepted Answer

Purines have a double ring structure (one six-membered and one five-membered ring), while pyrimidines have a single six-membered ring.

Question 2

A patient presents with hyperuricemia and swollen joints. Which enzyme deficiency is most likely responsible for these symptoms, and what is the biochemical consequence?

Accepted Answer

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency; accumulation of uric acid

Question 3

Which of the following statements about DNA structure is correct?

Accepted Answer

The sugar-phosphate backbone is on the outside, and the nitrogenous bases are on the inside of the helix.

Question 4

During DNA replication, which enzyme is responsible for relieving torsional strain ahead of the replication fork?

Accepted Answer

Topoisomerase

Question 5

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 in the 5' to 3' direction.

Question 6

Which of the following is a product of purine degradation in humans?

Accepted Answer

Uric acid

Question 7

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

Accepted Answer

It is overlapping, so one nucleotide can be part of more than one codon.

Question 8

Which of the following antibiotics inhibits RNA synthesis by binding to bacterial RNA polymerase?

Accepted Answer

Rifampin

Question 9

A mutation in the gene encoding DNA ligase would most directly affect which step of DNA replication?

Accepted Answer

Joining of Okazaki fragments on the lagging strand

Question 10

Which process is responsible for removing introns from pre-mRNA in eukaryotic cells?

Accepted Answer

Splicing

Question 11

Which of the following best describes semiconservative replication?

Accepted Answer

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

Question 12

Which of the following is the correct sequence of events during transcription initiation?

Accepted Answer

RNA polymerase binds to the promoter, DNA unwinds, ribonucleotides are assembled

Question 13

Which of the following codons is a stop codon in the genetic code?

Accepted Answer

UGA

Question 14

Which enzyme replaces RNA primers with DNA during DNA replication?

Accepted Answer

DNA polymerase I

Question 15

A patient with Lesch-Nyhan syndrome is unable to salvage purines. Which metabolic product is expected to be elevated in this patient?

Accepted Answer

Uric acid

Question 16

Which of the following modifications occurs at the 5' end of eukaryotic mRNA during maturation?

Accepted Answer

Capping

Question 17

Which of the following best describes the role of tRNA during translation?

Accepted Answer

It matches its anticodon with the mRNA codon and carries a specific amino acid.

Question 18

Which of the following is a direct result of a deficiency in pyrimidine phosphoribosyl transferase?

Accepted Answer

Impaired pyrimidine salvage pathway

Question 19

Which of the following statements about RNA and DNA is correct?

Accepted Answer

RNA is typically single-stranded, while DNA is double-stranded.

Question 20

Which of the following best explains why G-C base pairs are stronger than A-T base pairs in DNA?

Accepted Answer

G-C pairs form three hydrogen bonds, while A-T pairs form two.

Nucleic Acids: Structure, Synthesis, Replication, and Expression

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