Q: Which of the following equations correctly estimates the total length of DNA in a haploid human genome, given approximately $$3.2 \times 10^9$ base pairs and a spacing of 3.4$$ \text{\AA}$$ between base pairs?

$$3.4 \times 10$$^{-10}$$ \text{m} \times 3.2 \times 10^9$ \times 2$$

Question 1

Which of the following best explains how approximately 2 meters of human DNA is compacted to fit inside a nucleus with a diameter of 5-10 μm?

Accepted Answer

DNA is packaged into nucleosomes, which are further folded into higher-order chromatin structures.

Question 2

What is the basic structural unit of chromatin in eukaryotic cells, and how many base pairs of DNA does it typically contain?

Accepted Answer

The nucleosome, containing approximately 147 base pairs of DNA wrapped around a histone octamer.

Question 3

During which phase of the cell cycle are chromosomes most highly compacted and visible as distinct structures under a microscope?

Accepted Answer

Metaphase of mitosis

Question 4

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

Accepted Answer

Euchromatin is less compacted and generally associated with active gene expression.

Question 5

What is the function of the centromere in a chromosome?

Accepted Answer

It holds sister chromatids together and is the site of kinetochore formation.

Question 6

Which histone protein is specifically involved in the formation of higher-order chromatin structures beyond the nucleosome?

Accepted Answer

H1

Question 7

A mutation causes the loss of function of histone acetyltransferases (HATs) in a cell. What is the most likely effect on gene expression?

Accepted Answer

Decreased acetylation of histone tails and reduced gene expression.

Question 8

Which of the following best describes the role of ATP-dependent chromatin remodeling complexes?

Accepted Answer

They use energy from ATP hydrolysis to reposition or restructure nucleosomes, increasing DNA accessibility.

Question 9

In the context of cancer, why might histone deacetylase (HDAC) inhibitors be considered as a therapeutic strategy?

Accepted Answer

They prevent the removal of acetyl groups from histones, potentially reactivating tumor suppressor genes.

Question 10

Which of the following is NOT a possible mechanism by which chromatin remodeling increases local DNA accessibility?

Accepted Answer

DNA methylation at promoter regions

Question 11

A researcher observes that certain regions of a chromosome are highly repetitive and form key structural features such as centromeres and telomeres. These regions are most likely composed of:

Accepted Answer

Heterochromatin

Question 12

Which of the following equations correctly estimates the total length of DNA in a haploid human genome, given approximately $$3.2 	imes 10^9$ base pairs and a spacing of 3.4$$ 	ext{\AA}$$ between base pairs?

Accepted Answer

$$3.4 	imes 10$$^{-10}$$ 	ext{m} 	imes 3.2 	imes 10^9$ 	imes 2$$

Question 13

Which of the following best describes the difference between a chromatid and a chromosome?

Accepted Answer

A chromatid is one of two identical copies of a replicated chromosome, joined at the centromere.

Question 14

Which of the following is a correct statement about chromosome territories in the interphase nucleus?

Accepted Answer

Each chromosome occupies a discrete territory with limited intermingling with other chromosomes.

Question 15

Which of the following best explains why chromatin remodeling is essential for gene expression in eukaryotes?

Accepted Answer

It increases DNA accessibility, permitting transcription factors to bind and initiate transcription.

Question 16

Which of the following is a direct result of histone acetylation by histone acetyltransferases (HATs)?

Accepted Answer

Decreased positive charge on histone tails, resulting in relaxed chromatin and increased gene expression.

Question 17

A cell is observed to have chromosomes with highly condensed, dark-staining regions at the nuclear periphery during interphase. These regions are most likely:

Accepted Answer

Heterochromatin, which is transcriptionally inactive.

Question 18

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

Accepted Answer

A nucleosome consists of 8 histone proteins (2 each of H2A, H2B, H3, and H4) with 147 base pairs of DNA wrapped around them.

Question 19

Which of the following is NOT a structural feature of a typical eukaryotic chromosome?

Accepted Answer

Plasmid

Chromosome Structure and Chromatin Organization

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