$$\text{Hemimethylated DNA} \xrightarrow{\text{DNMT1/MET1}} \text{Fully methylated DNA}$$

Question 1

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

Accepted Answer

A nucleosome consists of DNA wrapped twice around a histone octamer, which includes two copies each of H2A, H2B, H3, and H4.

Question 2

What is the primary function of histone acetylation at lysine 9 of histone H3 (H3K9ac)?

Accepted Answer

It promotes the formation of open euchromatin, making DNA accessible for transcription.

Question 3

Which equation best represents the symmetrical methylation of CG dinucleotides in mammals?

Accepted Answer

$$	ext{5'-CmeG-3'}$$

Question 4

During DNA replication, how is maintenance DNA methylation achieved?

Accepted Answer

A maintenance DNA methyltransferase recognizes hemimethylated CG dinucleotides and methylates the newly synthesized strand.

Question 5

Which mechanism describes the inheritance of histone methylation marks during DNA replication?

Accepted Answer

Dispersive mechanism, where parental nucleosomes are randomly distributed to daughter strands and reader-writer proteins restore marks.

Question 6

Which of the following statements about epigenetics is correct?

Accepted Answer

Epigenetics refers to heritable changes in phenotype or gene expression that do not involve alterations in the DNA sequence.

Question 7

Which enzyme is responsible for de novo DNA methylation in mammals?

Accepted Answer

DNMT3

Question 8

What is the effect of histone H3K9 methylation on chromatin structure?

Accepted Answer

It condenses chromatin into heterochromatin, making DNA inaccessible for transcription.

Question 9

Which of the following best describes the role of small RNAs in plant chromatin modification?

Accepted Answer

Small RNAs recruit chromatin-modifying enzymes to generate heterochromatin by RNA-directed DNA methylation.

Question 10

Which of the following is a consequence of defective DNA methylation in plants?

Accepted Answer

Transposable elements become active, leading to new insertions and potential mutations.

Question 11

Which equation represents the maintenance of DNA methylation after replication?

Accepted Answer

$$	ext{Hemimethylated DNA} \xrightarrow{	ext{DNMT1/MET1}} 	ext{Fully methylated DNA}$$

Question 12

Which chromatin state is most sensitive to DNase digestion?

Accepted Answer

Euchromatin, due to its open and accessible structure.

Question 13

Which protein domain is responsible for recognizing histone modifications?

Accepted Answer

Reader domain

Question 14

In the context of chromatin modifications, what is the function of a 'writer' domain?

Accepted Answer

It adds post-translational modifications such as methyl or acetyl groups to histone tails.

Question 15

Which of the following best explains why transposable elements are heavily methylated in plant genomes?

Accepted Answer

Methylation silences transposable elements, preventing their movement and maintaining genome stability.

Question 16

Which of the following is a real-world consequence of epigenetic changes in chromatin?

Accepted Answer

Epigenetic changes can lead to heritable gene silencing without altering the DNA sequence, affecting traits across generations.

Question 17

Which of the following best describes the role of siRNAs in RNA-directed DNA methylation in plants?

Accepted Answer

siRNAs guide a RISC-like complex to transposable element loci, recruiting de novo DNA methyltransferases to silence them.

Question 18

Which histone modification is most commonly associated with active, accessible chromatin?

Accepted Answer

Acetylation of histone H3 at lysine 9 (H3K9ac)

Question 19

Which of the following best describes the relationship between chromatin structure and gene expression?

Accepted Answer

Open euchromatin is accessible to transcription factors and RNA polymerase, promoting gene expression.

Lecture 24 (Unit 2)-- Chromatin Structure and Epigenetics: Mechanisms and Biological Implications

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