Q: If the DNA in a human chromosome averages $$1.5 \times 10^8$ nucleotide pairs, approximately how long would this DNA molecule be if stretched out, given that each nucleotide pair is about 0.34$ nm long?

$$1.5 \times 10^8$ \times 0.34 = 5.1 \times 10^7$ nm, or about 4 cm

Question 1

Which of the following best describes the difference between bacterial and eukaryotic chromosomes?

Accepted Answer

Bacterial chromosomes are circular and associated with specific proteins, while eukaryotic chromosomes are linear and associated with many proteins.

Question 2

If the DNA in a human chromosome averages $$1.5 	imes 10^8$ nucleotide pairs, approximately how long would this DNA molecule be if stretched out, given that each nucleotide pair is about 0.34$ nm long?

Accepted Answer

$$1.5 	imes 10^8$ 	imes 0.34 = 5.1 	imes 10^7$ nm, or about 4 cm

Question 3

What is the basic structural unit of chromatin in eukaryotic cells?

Accepted Answer

The nucleosome

Question 4

Which of the following statements about histones is correct?

Accepted Answer

Histones are proteins that DNA wraps around to form nucleosomes.

Question 5

During which phase of the cell cycle does chromatin become most condensed, forming visible metaphase chromosomes?

Accepted Answer

Metaphase

Question 6

Which property distinguishes heterochromatin from euchromatin?

Accepted Answer

Heterochromatin is more condensed and less accessible to transcription machinery than euchromatin.

Question 7

A mutation causes a cell to lose the ability to modify histones. Which process would be most directly affected?

Accepted Answer

Chromatin condensation and gene expression regulation

Question 8

Which of the following best explains why DNA must be packaged into chromosomes?

Accepted Answer

To fit the large amount of DNA into the small volume of the cell nucleus

Question 9

Which of the following is true about the nucleosome structure?

Accepted Answer

It consists of DNA wrapped around a core of eight histone proteins.

Question 10

If a scientist observes a region of chromatin that is highly condensed and stains darkly under a microscope, which type of chromatin is she most likely observing?

Accepted Answer

Heterochromatin

Question 11

Which of the following best describes the role of condensin proteins during mitosis?

Accepted Answer

They help coil and condense chromatin into visible chromosomes.

Question 12

A researcher finds that certain genes are not being expressed in a cell. Upon investigation, she finds these genes are located in regions of chromatin that are highly compacted. What is the most likely explanation?

Accepted Answer

The genes are located in heterochromatin, which is inaccessible to transcription machinery.

Question 13

Which of the following sequences correctly represents the levels of DNA packing from least to most condensed?

Accepted Answer

Nucleosome → 10-nm fiber → Looped domains → Metaphase chromosome

Question 14

Which of the following is a functional consequence of the difference between heterochromatin and euchromatin?

Accepted Answer

Genes in euchromatin are more accessible for transcription.

Question 15

Which of the following best explains why centromeres and telomeres are often found as heterochromatin?

Accepted Answer

Their DNA must remain tightly packed and generally inactive to maintain chromosome stability.

Question 16

A cell is observed with chromatin that appears as a diffuse mass under a light microscope. In which phase of the cell cycle is this cell most likely to be?

Accepted Answer

Interphase

Question 17

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

Accepted Answer

Increasing the number of chromosomes in a cell

Question 18

Which of the following best describes the relationship between DNA, histones, and nucleosomes?

Accepted Answer

DNA wraps around histone proteins to form nucleosomes.

Question 19

Which of the following would most likely result if a mutation prevented the formation of nucleosomes?

Accepted Answer

DNA would remain uncondensed and could not fit into the nucleus.

Chromosome Structure: DNA Packing and Chromatin Organization

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