Question

Which one of the following conditions described below woudl result in a gene being expressed?

	A.	The gene is located in euchromatin and the promoter is methylated.
	B.	The gene is located in euchromatin and the promoter is not methylated.
	C.	The gene is located in heterochromatin and the promoter is methylated.
	D.	The gene is located in heterochromatin and the promoter is not methylated.

Answer 1

ANSWER-

A-GENE IS LOCATED IN EUCHROMATIN AND THE PROMOTER IS METHYLATED.

EXPLANATION- Gene- is defined as the functional unit of inheritance OR   The DNA sequence coding for tRNA or rRNA molecule also define a gene.

Regulation of gene expression occur at various levels.

• Gene expression results in the formation of a polypeptide, it can be regulated at several levels.

In eukaryotes, the regulation could be exerted at

1. transcriptional level (formation of primary transcript),
2. processing level (regulation of splicing),
3. transport of mRNA from nucleus to the cytoplasm,
4. translational level.

In eukaryotes there are two additional complexity in processing RNA :- hnRNA undergo two additional processing called as capping and tailing. In capping an unusual nucleotide (methyl guanosine triphosphate) is added to the 5'-end of hnRNA. In tailing, adenylate residues (200-300) are added at 3'-end in a template independent manner. It is the fully processed hnRNA, now called mRNA, that is transported out of the nucleus for translation .

* Euchromatin is a lightly packed form of chromatin (DNA, RNA, and protein) that is enriched in genes, and is often under active transcription. Euchromatin comprises the most active portion of the genome within the cell nucleus. 92% of the human genome is euchromatic.

Heterochromatin- IT is densely packed form of chromatin which is mostly transcriptionally inactive.