Question 1

Which of the following statements best explains why DNA, and not protein, is considered the genetic material in most organisms?

Accepted Answer

DNA is only found where primary genetic functions occur, such as the nucleus, while proteins are found throughout the cell.

Question 2

In the Hershey-Chase experiment, which radioactive isotope was used to label DNA, and what was the key finding?

Accepted Answer

$$^{32}\mathrm{P}$$; DNA entered the bacterial cell and directed the production of new phages.

Question 3

Which of the following best describes the difference between purines and pyrimidines, as shown in the first image?

Accepted Answer

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

Question 4

Which chemical group is present in ribose but absent in deoxyribose, as shown in the second image?

Accepted Answer

A hydroxyl group ($$-OH) at $$the 2' carbon position

Question 5

Which of the following best explains why DNA with a higher percentage of G-C base pairs has a higher melting temperature ($$T_m$$)?

Accepted Answer

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

Question 6

During DNA replication in E. coli, which enzyme is responsible for removing RNA primers and filling in the resulting gaps with DNA?

Accepted Answer

DNA polymerase I

Question 7

Which of the following statements about nucleosomes, as depicted in the fourth image, is correct?

Accepted Answer

A nucleosome consists of DNA wrapped around a histone octamer, which includes two copies each of H2A, H2B, H3, and H4.

Question 8

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

Accepted Answer

They relieve supercoiling by cutting and rejoining DNA strands.

Question 9

Which of the following is a direct result of the semiconservative model of DNA replication, as demonstrated by the Meselson-Stahl experiment?

Accepted Answer

Each daughter DNA molecule consists of one old strand and one newly synthesized strand.

Question 10

Which of the following best explains the role of the sliding DNA clamp in DNA replication, as shown in the seventh image?

Accepted Answer

It increases the processivity of DNA polymerase by holding it onto the DNA template.

Question 11

Which of the following modifications to histones is most likely to relax chromatin structure and promote gene expression?

Accepted Answer

Acetylation of lysine residues on histone tails

Question 12

Which of the following is true regarding the directionality of DNA synthesis?

Accepted Answer

DNA synthesis occurs in the $$5' \rightarrow 3'$$ direction, adding nucleotides to the free $$3'-OH $$group.

Question 13

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

Accepted Answer

It extends the 3' end of linear chromosomes by adding repetitive DNA sequences.

Question 14

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

Accepted Answer

The genetic code is degenerate, meaning that most amino acids are specified by more than one codon.

Question 15

Which of the following best explains the wobble hypothesis in tRNA-codon pairing?

Accepted Answer

The third base of the codon can form non-standard base pairs, allowing one tRNA to recognize multiple codons.

Question 16

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

Accepted Answer

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

Question 17

Which of the following best describes the role of aminoacyl-tRNA synthetase in translation?

Accepted Answer

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

Question 18

Which of the following is a direct consequence of a nonsense mutation in a gene?

Accepted Answer

A premature stop codon is introduced, resulting in a truncated protein.

Question 19

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

Accepted Answer

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

Question 20

Which of the following is a function of the spliceosome during mRNA processing?

Accepted Answer

It removes introns from pre-mRNA and joins exons together.

DNA Structure, Chromatin Organization, and Replication: Study Notes for Genetics Students

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