Question

Modifications to chromatin can affect transcriptional activity by changing the accessibility of DNA to the transcription machinery. The given descriptions are examples of various processes that may or may not cause remodeling of chromatin. Match each description to the effect it has on transcriptional activity caused by chromatin remodeling. a. Activates b. Inactivates c. Activates and inactivates d. No effect

Answer 1

Modifications in chromatin affect transcriptional activity of the gene by changing the accessibility of DNA to the transcription machinery.

Explanation:

1. Activates: Histone acetyltransferases attach acetyl groups to the N-terminus of histones

2. Inactivates: Histone deacetylases remove acetyl groups from the N-terminus end of histones protein.

3. Activates and inactivates: There is Histone methylation occurs at various amino acids of histone.

4. No effect: RNA polymerase II binds to the start site of transcription and causes transcription.

Answer 2

Chromatin

Explanation:

In eukaryotic transcription initiation of a gene requires change in chromatin structure (chromatin remodeling) because promoter and other regulatory elements of DNA exposed after removal of histone core

Examples of various processes that may or may not cause remodeling of chromatin:

• Activates:

Histone acetyltransferase catalyses histone acetylation(addition of acetyl group) which occurs on lysine residue of H3 and H4 which is present in histone tail

Histone acetylation neutralises the positive charge of histone core and facilitate their dissociation, this favors gene expression

• Inactivates:

Histone deacetylase catalyses removal of acetyl group from histone tail and favors interaction of histones to DNA and always associated with gene repression

• Activates and inactivates:

Histone methylation occurs at different amino acids, for example: when occurs on lysine and arginine residue of H3 histone then it favors gene expression whereas when occurs on lysine residue of H4 histone, it favors gene repression

• No effect:

RNA Polymerase II binds to the start site of transcription(core promoter) and transcribes all types of mRNA and most of snRNA and miRNA