$$T_m = 4 \times (\# \text{ of G-C pairs}) + 2 \times (\# \text{ of A-T pairs})$$

Question 1

Which of the following correctly describes the difference between a nucleoside and a nucleotide?

Accepted Answer

A nucleoside contains a base and a pentose sugar; a nucleotide contains a base, a pentose sugar, and one or more phosphate groups.

Question 2

Which of the following bases is found in DNA but not in RNA?

Accepted Answer

Thymine

Question 3

The glycosidic bond in nucleotides connects which two components?

Accepted Answer

The base and the 1' carbon of the pentose sugar

Question 4

Which of the following is a purine base?

Accepted Answer

Adenine

Question 5

Which property of DNA is most responsible for its ability to store genetic information stably over generations?

Accepted Answer

The right-handed double helix stabilized by hydrogen bonding and base stacking

Question 6

Which equation can be used to estimate the melting temperature ($$T_m) of a $$DNA duplex based on its base composition?

Accepted Answer

$$T_m = 4 	imes (\# 	ext{ of G-C pairs}) + 2 	imes (\# 	ext{ of A-T pairs})$$

Question 7

A DNA molecule is found to have 30% adenine. According to Chargaff's rules, what is the expected percentage of guanine?

Accepted Answer

20%

Question 8

Which of the following statements about the structure of DNA is correct?

Accepted Answer

The two strands of DNA are antiparallel and held together by hydrogen bonds between complementary bases.

Question 9

Which of the following best explains why DNA with a higher G-C content has a higher melting temperature?

Accepted Answer

G-C pairs form three hydrogen bonds, which provide greater stability than the two bonds in A-T pairs.

Question 10

During DNA replication, which model was supported by the Meselson-Stahl experiment?

Accepted Answer

Semiconservative replication

Question 11

Which enzyme is responsible for synthesizing RNA from a DNA template during transcription?

Accepted Answer

RNA polymerase

Question 12

Which of the following is true regarding the directionality of nucleic acid synthesis?

Accepted Answer

Nucleic acids are synthesized in the 5' to 3' direction.

Question 13

Which of the following statements about the central dogma of molecular biology is correct?

Accepted Answer

Genetic information flows from DNA to RNA to protein.

Question 14

Which of the following is a function of restriction enzymes in molecular biology?

Accepted Answer

Cleaving double-stranded DNA at specific sequences

Question 15

Which of the following is true about the Sanger method of DNA sequencing?

Accepted Answer

It uses dideoxynucleotides (ddNTPs) to terminate DNA chain elongation.

Question 16

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

Accepted Answer

tRNA carries amino acids to the ribosome and matches them to the mRNA codon via its anticodon.

Question 17

Which of the following is a consequence of the hydrophobic effect in DNA structure?

Accepted Answer

Hydrophobic bases are stacked in the core of the helix, excluding water and stabilizing the structure.

Question 18

Which of the following statements about supercoiled DNA is correct?

Accepted Answer

Supercoiled DNA is more compact and migrates faster through an agarose gel than relaxed DNA.

Question 19

Which of the following is a key difference between the B-form and A-form helices of nucleic acids?

Accepted Answer

B-form is the most common form in cellular DNA, while A-form is found in double-stranded RNA and DNA-RNA hybrids.

Nucleic Acid Structure: Composition, Bases, and Double Helix Organization

Study Guide - Practice Questions