Question

Part 1. Eukaryotes use at least two distinct mechanisms to control gene expression by altering the structure of chromatin around a particular gene. One of these mechanisms is the covalent modification of histones to switch DNA between an open and closed confirmation. A second mechanism is the covalent modification of DNA (typically on cytosines) by methylation. A. Describe a type of histone modification and explain what effect is has on chromatin, and how that effect is achieved. a. One type of histone modification is histone methylation. This is the transfer of methyl groups to amino acids of histone proteins. It can decrease or increase transcription. Methylation turns "on" and "off" genes either through loosening their tails or encompassing their tails around the DNA. This loosening or tightening impacts its interactions with other proteins. unmethylated open DNA unmethylated closed DNA methylated closed DNA myosin neuropeptide DNA pol Gene A Gene B Gene C B. DNA methylation is a more long-term change in DNA packaging. Why? a. This is because it can turn "on" or "off genes, allowing for more change as time goes on. C. A particular region of the genome has the following 3 genes: Gene A codes for myosin, a critical protein in muscles; Gene B codes for a neuropeptide, a signaling molecule used by neurons; Gene C codes for DNA polymerase. Diagram how the genome would look for genes A and B in each of the following cell types: neuron cell, muscle cell, liver cell.

Answer 1

A) methylation of histone protein done by histone methyl transferase enzyme. methylation of specific tail residue and degree of methylation on histone molecules leads to activation or inactivation of transcription. Most common methylated amino acids are lysine (K) and arginine (R) .   most commonly observed methylation is on lysine residues of histone tails H3 and H4. Methylation of some histone leads to activation of transcription while some type of methylation lead to transcription repression.

For example methylation of H3K4, H3K48, and H3K79.- associated with activation of that gene

While H4K20 methylation lead to change in histone such a way that it bind to some repressor protein and interfere in binding of transcription factors thus repression of transcription.

B) in DNA methylation, methyl group is added in DNA bases and affect expression of gene by interfering binding of various factors to DNA . So this methylation alter the gene expression and has long term effects on gene expression .

C) in our body ,each cell has similar genome but there is tissue specific expression of gene occur.

Here 3 genes, each has specific role

Myosine -- role in muscle -- should be expressed in muscle not in brain or in liver

Neuropeptide -- play an important role in brain . Should be expressed in brain only not in liver or muscle

For DNA polymerase- involves in replication , as neurons are known as non dividing cells so DNA polymerase gene must be less expressed here. While muscle invovle in synthesis of muscle cells which are slowly dividing cells  and liver cells are rapidally dividing cells so exist in open form.

For more clear understanding, image has been attached.

Muscle: Newan -wyokin bat open t expression Nettes peptide Continuous requirment for mountain remen health Toob por e Neuropeptid. methylated closed - No expressim methyl gostne Methyl atcel coxed - no requirement in un om polynean om - Doo paly, - Slow expression compared to open as -slow Neures divide expressin cels do not fast bra polynenant ngoxin (net requise in Leer). NORAT Neuropeptrode suust be in metrylates form ( not required)