Q: Which of the following equations correctly represents the ratio of basic to acidic amino acids in histone proteins, and why is this ratio important?

$$\frac{\text{Number of basic amino acids}}{\text{Number of acidic amino acids}}$$; a high ratio enables strong binding to negatively charged DNA

Question 1

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

Accepted Answer

An octamer of histones (two each of H2A, H2B, H3, and H4) wrapped by approximately 146 bp of DNA

Question 2

During DNA replication, how are nucleosomes inherited by daughter chromatids?

Accepted Answer

H3-H4 tetramers are randomly distributed to one of the sister chromatids, while H2A-H2B dimers are reassembled from both old and new histones

Question 3

Which of the following statements about heterochromatin is correct?

Accepted Answer

Heterochromatin is highly condensed and generally transcriptionally inactive

Question 4

A mutation causes the spreading of heterochromatin into a normally euchromatic region near a gene in Drosophila. What is the most likely effect on gene expression in that region?

Accepted Answer

Gene expression will be silenced or reduced due to chromatin compaction

Question 5

Which chemical modification is most commonly associated with gene activation in chromatin?

Accepted Answer

Histone acetylation at H3K9

Question 6

What is the primary function of 'reader' proteins in the context of the histone code?

Accepted Answer

They recognize and bind to specific histone modifications to mediate downstream effects

Question 7

Which of the following best explains the role of scaffold proteins in chromatin organization?

Accepted Answer

They help organize higher-order chromatin structures beyond the 30 nm fiber

Question 8

If a mutation prevents the acetylation of histone H3 at lysine 9 (H3K9ac), what is the most likely consequence for gene expression in the affected region?

Accepted Answer

Gene expression will decrease due to chromatin remaining condensed

Question 9

Which of the following equations correctly represents the ratio of basic to acidic amino acids in histone proteins, and why is this ratio important?

Accepted Answer

$$\frac{	ext{Number of basic amino acids}}{	ext{Number of acidic amino acids}}$$; a high ratio enables strong binding to negatively charged DNA

Question 10

A researcher uses the CUT&RUN technique to study histone modifications. What is the main advantage of this method compared to traditional chromatin immunoprecipitation (ChIP)?

Accepted Answer

CUT&RUN provides higher resolution mapping of protein-DNA interactions with less background noise

Question 11

Which of the following best describes the hierarchical folding of the eukaryotic genome?

Accepted Answer

DNA wraps around histones to form nucleosomes, which further fold into 30 nm fibers and higher-order domains such as TADs

Question 12

Which of the following is a function of nonhistone proteins in chromatin?

Accepted Answer

They perform diverse roles such as DNA replication, repair, and regulation of gene expression

Question 13

A scientist observes that a region of chromatin switches between being transcriptionally active and inactive in response to environmental signals. What is this region most likely classified as?

Accepted Answer

Facultative heterochromatin

Question 14

Which of the following best explains the 'histone code' hypothesis?

Accepted Answer

Combinations of chemical modifications to histone tails specify distinct chromatin states and gene expression outcomes

Question 15

Which enzyme type is responsible for removing acetyl groups from histone tails, and what is the likely effect on chromatin structure?

Accepted Answer

Eraser enzymes; chromatin becomes more condensed

Question 16

A patient has a mutation in a gene encoding a chromatin 'writer' enzyme. Which of the following is a likely consequence?

Accepted Answer

The patient may have abnormal patterns of histone modification, leading to misregulation of gene expression

Question 17

Which of the following is a correct sequence of events in the assembly of the nucleosome core particle?

Accepted Answer

H3-H4 dimers form a tetramer, then two H2A-H2B dimers associate to form the octamer

Question 18

Which of the following histone modifications is most commonly associated with gene silencing?

Accepted Answer

H3K9me3 (trimethylation of lysine 9 on histone H3)

Question 19

Which of the following best describes the function of topologically associating domains (TADs) in the genome?

Accepted Answer

TADs are spatially distinct regions of the genome that facilitate regulatory interactions within the domain

Eukaryotic Chromosome Organization and Chromatin Structure

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