Question

1a. Histone acetylation (addition of acetyl groups) is associated with ___ gene expression. (mark your answer with an X)

            ___ decreased                         ___ increased

b. Why does acetylating histones have this effect?

c. Acetyl groups can be removed by what type of enzyme?

d. These enzymes (answer to c) are recruited by: (mark your answer with an X)

            ___ activators                          ___ repressors

Answer 1

1a. Histone acetylation (addition of acetyl groups) is associated with increased gene expression.

1b. Histone acetylation plays a major role in gene transcription and is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDAC). Because of the presence of the -NH2 group, lysine is positively charged and thus is strongly bound to the negatively charged DNA. When the acetyl group is added to the lysine of the histone proteins, the positive charge gets neutralized and this results in reduced binding of histones and DNA. This open structure is thus more accessible to the transcriptional machinery and hence acetylation leads to transcriptional activation.

1c. The enzyme which removes the acetyl group is a histone deacetylase (HDAC), these enzymes counteract the effect of acetyltransferase (HAT).

1d. These enzymes (answer to c) are recruited by repressors

(DNA-binding repressors are involved in recruiting Rpd3 histone deacetylase complexes to the promoters. Thus histone acetylases are recruited by activators and histone deacetylases by repressors).