Question

Which of these mechanisms exerts gene control by suppressing transcription in eukaryotes?

Answer 1

A: acetylation of histone protiens.
B. Methylation of DNA
C. Action of Activatior protiens

Answer 2

You could probably easily rule out C, because activator proteins (as their name suggests) help enhance transcription.

As for the other two - take a look at the structure of an acetyl group, and note that it is a polar molecule. Consider the effects of attaching a polar molecule onto the positive histone proteins, and the resulting change in how it binds to DNA.

In regards to methylation of DNA, this is an action taken by the cell to (in most cases) silence transcription...how it does so, I'm not too certain, but I do suggest you read into it.

Answer 3

I believe that DNA methylation suppresses transcription by preventing transcription factors from binding. These transcription factors are proteins that are exquisitely structured so that they bind just so to a particular region of DNA - and sticking a bulky methyl group on the DNA makes it impossible for the transcription factors to recognize and bind targets.

Whether it has any effect on the histones and other DNA scaffolding proteins - i.e., makes the methylated DNA pack tightly - I, erm, don't know. And shall look up. Classic @ebaxter01 question.

Answer 4

From what I remember the methylation leads to binding of repressive proteins to the DNA. An example of one of these is MeCP2 (methyl CpG binding protein 2). This can interact with proteins which have a repressive effect on chromatin structure such as Sin3/ histone deacetylase complex. The DNA is more tightly packed when associated with deacetylated histones than when bound to acetylated histones. Most of the DNA in a nucleus is in this methylated state, including the large amount of repetitive DNA in cells. DNA methylation is also the basis of genomic imprinting which is an interesting subject but I don't want to get too complex just now.