Which statements about the modification of chromatin structure in eukaryotes are true?
A. DNA is not transcribed when chromatin is packaged tightly in a condensed form
B. Some forms of chromatin modification can be passed on to future generations of cells
C. Acetylation of histone tails in chromatin allows access to DNA for transcription
D. Acetylation of histone tails is a reversible process.
E. Methylation of histone tails in chromatin can promote condensation of the chromatin
F. Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA.
The correct options are A, C, D, E, and F.
The correct answers are:
• Methylation of histone tails in chromatin can promote condensation of the chromatin.
• DNA is not transcribed when chromatin is packaged tightly in a condensed form.
• Acetylation of histone tails is a reversible process.
• Some forms of chromatin modification can be passed on to future generations of cells.
• Acetylation of histone tails in chromatin allows access to DNA for transcription.
Chromatin and DNA transcription:
DNA is present in the membrane-bound nucleus of eukaryotic cells. It carries our genetic information.
In eukaryotic cells, the DNA is combined with histones, which are proteins—these proteins, when bonds with DNA, form a complex and packaged structure called a nucleosome.
Four of the histones that form a structure is called as Octamer. These four proteins are H2B, H2A, H3, and H4.
This chromatin is called heterochromatin when it is in packed form. When it became less tightly, gene transcription occurs at that point, which is known as euchromatin. In transcription, the DNA sequence is copied into mRNA strand.
Histone modifications have to affect gene expression by changing the chromatin structure or recruiting histone modifiers. The most common adaptations are Methylation, Acetylation, phosphorylation, and ubiquitylation. All of them affect the binding between DNA and histones, thus loosening or tightening the condensed DNA.
Many different modifications happen on the histones. Both Acetylation and deacetylation are essential in the regulation of genes.
The mechanism in which an acetyl group is combined with histones at a certain point. It helps to loosen and unpack the chromatin to facilitate the gene transcription process. It helps in protein synthesis. Deacetylation is the reverse process.
The process when a methyl group is combined with chromatin is called Methylation. It can have an effect of suppressing or stimulating gene transcription. This effect of methyl group addition depends on histone protein. Demethylation is the reverse process.
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