Question

Which statements about the modification of chromatin structure in eukaryotes are true? Select all that apply. View Available Hint(s) Acetylation of histone tails is a reversible process Some forms of chromatin modification can be passed on to future generations of cells. DNA is not transcribed when chromatin is packaged tightly in a condensed form. O Acetylation of histone tails in chromatin allows access to DNA for transcription. Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA Methylation of histone tails in chromatin can promote condensation of the chromatin

Answer 1

All of the offered answers are correct:  

• Some forms of chromatin modification can be passed on to future generations of cells.

This is the part of epigenetics which studies heritable phenotype changes that do not involve alterations in the DNA sequence and most often changes that affect gene activity and expression.

• Acetylation of histone tails is a reversible process.

Histone acetylation is a process of histone modification that occurs by the enzymatic addition of an acetyl group (COCH3) from acetyl coenzyme A via histone acetyltransferases (HATs). On the other hand, histone deacetylaces (HDACs) are the enzymes that  catalyze the hydrolytic removal of acetyl groups which is the opposite process of acetylation.

• DNA is not transcribed when chromatin is packaged tightly in a condensed form.

When chromatin is in condensed form (associated with structural proteins in heterochromatin) that means that genes areinactive ("turned off").

• Acetylation of histone tails in chromatin allows access to DNA for transcription.

Histone acetylation is often associated with an open chromatin structure meaning that it promotes transcription and increase gene expression.

Methylation of histone can have different effects on transcription (it is implicated in both transcriptional activation and repression) depending on the methylation site. For example, arginine methylation promotes transcriptional activation, while lysine methylation can promote activation and repression (condensation of the chromatin).

Answer 2

Answer:

Acetylation of histone tails is a reversible process.

DNA is not transcribed when chromatin is packaged tightly in a condensed form.

Methylation of histone tails in chromatin can promote condensation of chromatin.

Acetylation of histone tails in chromatin allows access to DNA for transcription.

Eukaryotic chromatin structure is a highly complex assembly which needs to be simplified in order to undergo process of transcription. Eukaryotic chromatin structure is highly condensed in nature and DNA cannot be access for transcription. Actylation of histone tails is a process in which breaks the bond of attraction between adjacent nucleosomes. It results in chromatin being condensed attains a loose form. Transcription of DNA can occur in a loose chromatin. Methylation can promote condensation or decondensation of chromatin structure depending upon the methyl group present in the histone.