Final answer:
Adding acetyl groups to histones leads to increased transcription and gene expression. Adding Me3 can result in reduced transcription and gene expression. Methylation of CPG islands leads to gene silencing.
Step-by-step explanation:
a. adding acetyl groups: Adding acetyl groups to the lysine tails of histones has the effect of loosening the packaging of DNA around the histones. This opens up the chromatin structure, allowing for easier access of transcription factors and RNA polymerase to the DNA, leading to increased transcription and gene expression.
b. adding Me3: Adding Me3 (methyl groups) to the lysine tails of histones can have different effects on transcription depending on the specific lysine residue that is methylated. Generally, adding Me3 can result in the tightening of the chromatin structure, making the DNA less accessible and reducing transcription and gene expression.
d. adding methyl groups to CPG islands: Adding methyl groups to CPG islands, which are regions rich in cytosine-guanine dinucleotides, can lead to gene silencing. Methylation of CPG islands is associated with a closed chromatin structure and decreased accessibility of DNA to transcription factors, resulting in reduced gene expression.
e. removing nucleosomes from promoter regions: Removing nucleosomes from promoter regions results in the opening up of chromatin structure, allowing for easier access of transcription factors to DNA and promoting transcription and gene expression.
Overall, the compounds added to the lysine tails of histones can have different effects on transcription depending on the specific modification and the context in which it occurs.