Question 1

Which of the following best explains why DNA must be compacted within the nucleus of a eukaryotic cell?

Accepted Answer

To allow DNA to fit inside the small volume of the nucleus and protect it during cell division

Question 2

Which protein is primarily responsible for the initial packaging of DNA into nucleosomes in eukaryotic cells?

Accepted Answer

Histone

Question 3

A nucleosome consists of DNA wrapped around a histone octamer. Which histone types are found in the core octamer?

Accepted Answer

H2A, H2B, H3, H4

Question 4

Which chemical modification of histones is most commonly associated with increased gene expression?

Accepted Answer

Acetylation of lysine

Question 5

During mitosis, chromatin fibers undergo further compaction to form visible chromosomes. What is the main function of this process?

Accepted Answer

To ensure accurate segregation of DNA to daughter cells

Question 6

Which of the following statements about euchromatin and heterochromatin is correct?

Accepted Answer

Euchromatin is lightly packed and transcriptionally active

Question 7

Which enzyme is responsible for adding acetyl groups to histone proteins, thereby promoting gene activation?

Accepted Answer

Histone acetyltransferase (HAT)

Question 8

In eukaryotic cells, which level of DNA organization immediately follows the 'beads on a string' structure?

Accepted Answer

30 nm chromatin fiber

Question 9

Which of the following is true regarding DNA methylation in eukaryotes?

Accepted Answer

Methylation of cytosine is usually negatively correlated with gene activity

Question 10

A researcher is studying a region of chromatin that is highly acetylated and lightly packed. Which type of chromatin is she most likely observing?

Accepted Answer

Euchromatin

Question 11

Which of the following best describes the role of linker histone H1?

Accepted Answer

It binds to linker DNA and helps stabilize higher-order chromatin structure

Question 12

Which of the following equations best represents the relationship between the number of base pairs ($$bp) $$and the length of DNA ($$L) in $$nanometers, given that the distance between adjacent base pairs is approximately $$0.34 nm$$?

Accepted Answer

$$L = bp 	imes 0.34$$

Question 13

A mutation prevents the acetylation of lysine residues on histone proteins. What is the most likely effect on gene expression in the affected region?

Accepted Answer

Gene expression will decrease due to chromatin compaction

Question 14

Which of the following is NOT a function of chromatin remodeling?

Accepted Answer

Increasing the rate of DNA mutation

Question 15

In prokaryotes, DNA is compacted primarily by which mechanism?

Accepted Answer

Supercoiling

Question 16

Which of the following statements about plasmids is correct?

Accepted Answer

Plasmids are small, circular, extrachromosomal DNA molecules that replicate independently

Question 17

Which of the following best describes the hierarchical levels of DNA organization in eukaryotes, from least to most compact?

Accepted Answer

Double helix, nucleosome, chromatin, chromosome, genome

Question 18

A scientist observes that a particular gene is located in a region of DNA that is densely packed and transcriptionally inactive. Which type of chromatin is this gene most likely associated with?

Accepted Answer

Heterochromatin

Question 19

Which chemical modification of DNA is most often associated with gene silencing in eukaryotes?

Accepted Answer

Methylation of cytosine

Question 20

If a human cell contains approximately $$2$$ meters of DNA and the nucleus is only $$5$$ micrometers in diameter, what is the approximate compaction ratio required to fit the DNA inside the nucleus? (Assume $$1$$ meter $$= 10^6$ micrometers)

Accepted Answer

$$2 	imes 10^6$ \div 5 = 400,000$$

DNA Organization in Eukaryotes and Prokaryotes

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