In-Class Exam 2 Questions with Complete

In-Class Exam 2 Questions with Complete Solutions (Latest 2025)

• DNA is more suitable than RNA to serve as genetic

material. One of the reasons is that

• DNA is a much more stable molecule due to the lack of 2'-

OH group on the sugar component.

• DNA can exist in A form, B form, and Z-form, thus its

structure is much more diverse than RNA.

• RNA can not function as a template to direct the synthesis

of a complementary strand.

• It takes less energy to synthesize DNA, thus it is more

economical to use DNA as genetic material. - Correct Answers ✅A) DNA is a much more stable molecule due to the lack of a 2'-OH on the sugar component

2. Considering the two molecules shown on the right: which

of the following statements is correct?

• The glycosidic bonds of both molecules are in syn

conformation.

• These two molecules are guanosine (top) and

deoxycytidine (bottom).

• These two molecules are adenosine (top) and cytidine

(bottom).

• Both molecules can be used by DNA polymerase as a

substrate for DNA 1 / 3

In-Class Exam 2 Questions with Complete Solutions (Latest 2025) synthesis - Correct Answers ✅B) these two molecules are guanosine (top) and deoxycytidine (bottom)

• Which of the following accurately describes the properties

of the common form of DNA double helix?

• A helical turn consists of about 3.4 nucleotides.
• The nitrogenous bases are exposed to the solvent,

whereas the sugar-phosphate backbone of each strand is on the interior of the double helix.

• The phosphodiester bonds between nucleotide residues

run in opposite directions in the two strands.

• All of the above. - Correct Answers ✅C) the

phosphodiester bonds between nucleotide residues run in opposite directions

• Which of the following statements is correct regarding the

two circular DNA molecules shown here?

• These two molecules have the same writhing number.
• These two molecules are essentially the same molecule

but their linking numbers are different.

• These two molecules have the same linking number, but

their twisting 2 / 3

In-Class Exam 2 Questions with Complete Solutions (Latest 2025) numbers and writhing numbers are different.

• It is hard to tell if these two molecules have the same

twisting number. - Correct Answers ✅C) these two molecules have the same linking number, but their twisting and writhing numbers are different

5. B-form DNA has the following features:

• Left-handed, wide and deep major groove, antiparallel

strands

• Most stable form under physiological conditions, wide and

deep major groove, with base-pairs nearly perpendicular to the axis of the helix

• Favored form of dehydrated DNA, antiparallel strands
• Containing purines in syn-conformation, the most common

form of DNA found in cells - Correct Answers ✅B) most stable form under physiological conditions, wide and deep major groove, with base-pairs nearly perpendicular to the axis of the helix

• The double helical structure shown here is
• right-handed B) left-handed
• ambidextrous D) cannot tell - Correct Answers ✅B) left-

handed

• Binding of DNA by transcriptional regulators typically

occurs on major grooves of DNA because

• / 3