The following enzymes or processes are known to regulate eukaryotic gene expression. in the blank provided by each enzyme or process, enter the number 1 if the enzyme or process increases gene expression or the number 2 if the enzyme or process decreases gene expression.

(a) histone acetyltransferases (hats)
(b) histone deacetylases (hdacs)
(c) acetylation
(d) deacetylation
(e) decreased attaraction between dna and histones
(f) increased attraction between dna and histones

a) 1 b) 2 c) 1 d) 2 e) 1 f) 2

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.

when a reversible reaction is occurring in both directions at the same rate; the products and reactants do not change in concentration. a chemical reaction where the compound is broken into its constituent parts.

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