Answer:
a) 1 b) 2 c) 1 d) 2 e) 1 f) 2
Step-by-step explanation:
a) A coactivator CBP contains a subunit that has histone acetyltransferase (HAT) activity. These enzymes transfer acetyl groups from an acetyl CoA donor to the amino groups of specific lysine residues on histone proteins.
-Gradually this leads to activation of several other coactivators and as a result initiation of transcription takes place.
b) HDACs are associated with transcriptional repression. HDACs are present as subunits of larger complexes described as corepressors.
-Corepressors are similar to coactivators, except that they are recruited to specific genetic loci by transcriptional factors (repressors) that cause the targeted gene to be silenced rather than activated.
c) Acetylation of histone residues is thought to prevent chromatin fibers from folding into compact structures, which helps to maintain active, euchromatic regions.
-On a finer scale, histone acetylation increases access of specific regions of the DNA template to interacting proteins, which promotes transcriptional activation.
d) Deacetylation of the the histone tails makes the DNA more tightly wrapped around the histone cores, making it difficult for transcription factors to bind to the DNA. This leads to decreased levels of gene expression.
e) Decreased attraction is directly proportional to loosening of the DNA from histone core hence accessible to the transcriptional factors which further leads to transcription and gene expression
f) Increased attraction means DNA gets tightly wound around the histone core and inaccessible to the transcription factor hence decreased gene expression.