Question 1

Which of the following statements best explains why DNA, and not protein, was ultimately identified as the genetic material in cells?

Accepted Answer

Proteins are more chemically complex than DNA, but experiments showed that only DNA could transform non-pathogenic bacteria into pathogenic forms.

Question 2

A scientist isolates a nucleic acid from a virus and finds that it contains uracil but no thymine. Which conclusion is most likely correct?

Accepted Answer

The viral genetic material is RNA.

Question 3

According to Chargaff’s rules, if a DNA sample contains 30% adenine, what percentage of guanine would you expect to find?

Accepted Answer

$$20\%$$

Question 4

Which feature distinguishes B-DNA from Z-DNA?

Accepted Answer

B-DNA is a right-handed helix with clear major and minor grooves, while Z-DNA is a left-handed helix with a disordered structure.

Question 5

Which enzyme is responsible for introducing transient double-strand breaks in DNA to manage supercoiling?

Accepted Answer

Type II topoisomerase

Question 6

A DNA sample is heated and its absorbance at $$260\ \mathrm{nm}$$ increases. What is the most likely explanation for this observation?

Accepted Answer

The DNA strands are denaturing, causing the bases to become unstacked and absorb more light.

Question 7

Which of the following best describes the structure of a nucleosome?

Accepted Answer

A histone octamer with approximately $$146$$ base pairs of DNA wrapped around it

Question 8

Which histone modification is most likely to result in increased gene expression?

Accepted Answer

Acetylation of histone tails

Question 9

A mutation prevents the formation of nuclear localization signals (NLS) on a protein. What is the most likely consequence?

Accepted Answer

The protein will remain in the cytoplasm and not enter the nucleus.

Question 10

Which of the following is a function of telomeres in eukaryotic chromosomes?

Accepted Answer

Protecting chromosome ends from shortening during replication

Question 11

Which of the following best explains why highly repeated DNA sequences renature more quickly than unique sequences after denaturation?

Accepted Answer

Their high concentration increases the likelihood of complementary strands finding each other.

Question 12

Which of the following statements about chromatin structure is correct?

Accepted Answer

Euchromatin is less tightly packed and more transcriptionally active than heterochromatin.

Question 13

Which of the following is true regarding the nuclear pore complex (NPC)?

Accepted Answer

It is composed of about $$30$$ different proteins called nucleoporins.

Question 14

A researcher finds a circular DNA molecule in a eukaryotic cell that lacks histones. This DNA is most likely from which cellular structure?

Accepted Answer

Mitochondrion

Question 15

Which of the following best describes the role of Ran-GTP in nuclear transport?

Accepted Answer

It promotes the release of NLS-containing cargo from importin inside the nucleus.

Question 16

Which of the following is a characteristic of LINEs (long interspersed nuclear elements) in the human genome?

Accepted Answer

They are $$6000$$–$$8000$$ base pairs long and contain genes for their own mobilization.

Question 17

A cell is observed to have a high level of histone acetylation and active chromatin remodeling complexes. What is the most likely state of its chromatin?

Accepted Answer

Open and transcriptionally active

Question 18

Which of the following best describes the function of cohesin proteins in chromatin structure?

Accepted Answer

They stabilize DNA loops within the 30-nm chromatin fiber.

Question 19

If the human genome contains $$3.2 	imes 10^9$ base pairs and each base pair is 0.34$ nm long, what is the total length of the human genome in meters?

Accepted Answer

$$1.088$$ meters

The Structural Basis of Cellular Information: DNA, Chromosomes, and the Nucleus

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