Question

2. Give 2-3 examples of gene regulation in eukaryotes. Define what they are and how they specifically regulate gene expression 3. What is histone acetyltransferase enzyme? How does it regulate gene expression? Explain your reasons 4. What is chromatin remodeling in general? 5. What is DNA methylation? What does methylation mean in this case? How does it intervene gene expression? Explain your reason

Answer 1

2. Examples of gene regulation in eukaryotes are-

i) Regulation by chromatin remodeling

ii) Regulation by Trp Operon

i) In chromatin remodeling the enhancers loosen the tightly bound DNA and histone or sometimes break the nucleosome structure for synthesis of RNA by RNA polymerase.

ii) Trp Operon us an example of repressible negative regulation of gene expression. It regulates by both repression and attenuation.

• When tryptophan us present , the repression mechanism occurs . Tryptophan reprressior dimers bound to the tryptophan, causing the change in the reprressior confirmation, allowing the reprressior to bind to the operator. This prevents RNA polymerase from binding to and transcribing the operon, and tryptophan is not produced.
• Attenuation responds to the concentration of the charged tRNA of tryptophan. Thus attenuation dose by altering the process of transcription that already in progress.

3. Histone acetyltransferases are enzymes that acetylate conserved lysine amino acids on histone by transferring acetyl group.

• As DNA wrapped around histones, by transferring an acetyl group to the histone from acetyl co-A , genes can be turned on and off.

4. In eukaryotes the DNA is exists as nucleosome, that is DNA is tightly bound to the histone proteins. The nucleosome forms a chromatin fiber when other protein binds to it. RNA polymerase can't bind to the DNA and synthesize RNA as the DNA and histone bound together. The enhancers loosen the binding between the histones and DNA or sometimes break the nucleosome structure in order to promote RNA synthesis by RNA polymerase. This process is known as chromatin remodeling as it changes the nucleosome structure.

5.DNA methylation is a process by which methyl groups are added to the DNA molecule.

• Here methylation means addition of methyl group to DNA nucleotide for activation or inhibition of gene activity.

Methylation can change the activity of a DNA segment without changing the sequence. When located in a gene promoter, DNA methylation typically acts to repress gene transcription.

DNA methylation is essential for normal development and is associated with a number of processes including genomic imprinting, repression of aging, transposable elements etc.