Question 1

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

Accepted Answer

A DNA double helix wrapped around a histone octamer, consisting of two copies each of H2A, H2B, H3, and H4.

Question 2

What is the approximate length of DNA wrapped around a nucleosome core particle?

Accepted Answer

$$147$$ base pairs

Question 3

Which histone is primarily associated with the linker DNA between nucleosomes and helps in higher-order chromatin structure?

Accepted Answer

Histone H1

Question 4

Which chromatin type is generally associated with active gene transcription?

Accepted Answer

Euchromatin

Question 5

A mutation causes the loss of a barrier protein between euchromatin and heterochromatin. What is the most likely consequence?

Accepted Answer

Heterochromatin may spread into euchromatin regions, silencing previously active genes.

Question 6

Which histone modification is most commonly associated with gene silencing in heterochromatin?

Accepted Answer

Trimethylation of lysine 9 on histone H3 ($$H3K9me3)$$

Question 7

Which of the following best explains the 'beads-on-a-string' structure observed in chromatin?

Accepted Answer

Nucleosomes connected by linker DNA, resembling beads on a string under electron microscopy.

Question 8

Which of the following is a function of non-histone proteins in chromatin?

Accepted Answer

Regulation of gene expression

Question 9

A cell is observed to have a high abundance of trimethylated $$H3K27$$ marks. What is the most likely state of the genes in this region?

Accepted Answer

Developmentally repressed and transcriptionally inactive

Question 10

Which of the following statements about heterochromatin is TRUE?

Accepted Answer

It is highly organized and restricts gene expression.

Question 11

Which DNA sequence context is preferred for nucleosome positioning due to its ability to bend easily around the histone core?

Accepted Answer

AA, TT, and TA dinucleotides

Question 12

What is the role of 'reader' proteins in chromatin regulation?

Accepted Answer

They recognize specific histone modifications and recruit other proteins to alter chromatin structure.

Question 13

Which of the following is a direct consequence of histone tail phosphorylation?

Accepted Answer

Altered chromatin structure and potential changes in gene expression

Question 14

A chromosome translocation places a gene normally in euchromatin next to heterochromatin. What is a likely outcome?

Accepted Answer

The gene may become silenced due to heterochromatin spreading.

Question 15

Which histone variant is specifically involved in centromere function and kinetochore assembly?

Accepted Answer

CENP-A

Question 16

Which of the following best describes facultative heterochromatin?

Accepted Answer

Chromatin that can switch between active and inactive states depending on developmental or environmental cues.

Question 17

Which process is most likely to be affected if the histone fold domain is mutated?

Accepted Answer

Assembly of the histone octamer and nucleosome formation

Question 18

Which equation best represents the number of nucleosomes ($$N) $$that can be formed from a DNA molecule of length $$L$$ base pairs, given that each nucleosome core wraps $$147$$ base pairs and the average linker DNA is $$53$$ base pairs?

Accepted Answer

$$N = \frac{L}{147 + 53}$$

Question 19

Which of the following is a real-life example of the importance of chromatin structure in human health?

Accepted Answer

Mutations in barrier proteins can lead to inappropriate gene silencing, contributing to diseases such as cancer.

Question 20

Which of the following statements about nucleosome dissociation is correct?

Accepted Answer

High concentrations of salt can dissociate nucleosomes into histone octamers and free DNA.

Chromatin Structure and Function: Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard