Question

When DNA is compacted by histones into 10-nm and 30-nm fibers, the DNA is unable to interact with proteins required for gene expression. Therefore, to allow for these proteins to act, the chromatin must constantly alter its structure. Which processes contribute to this activity?

	a.	nucleotide removal
	b.	hydrolysis of DNA molecules where they are wrapped around the nucleosome core
	c.	DNA coiling at or around H1
	d.	accessibility of heterochromatin to deacetylase enzymes
	e.	acetylation of histone proteins

What accounts for a small number of protein-coding genes as compared to the larger number of proteins made by human cells?

	a.	alternative splicing
	b.	enhancers
	c.	miRNA
	d.	protein degradation
	e.	operons

Deletion mutations were created to determine the location and function of possible upstream regulatory sequences. The following results were obtained.

E.g., Deletion region ^-10 - ^-30 means that the region 10-30 nucleotides upstream of transcription start were deleted and the transcription rate was reduced to 0%.

Which mutation represents the deletion of an enhancer?

Mutant	Deletion Region	% Transcription
Wild Type	None	100%
A	-10 — -30	0%
B	-30 — -100	50%
C	-500 — -700	100%
D	-700 — -900	45%
E	-900 — -1100	30%
F	-1100 — -1300	100%
G	-1300 — -1500	150%

	a.	G
	b.	F
	c.	A
	d.	B
	e.	E

Deletion mutations were created to determine the location and function of possible upstream regulatory sequences. The following results were obtained.

E.g., Deletion region ^-10 - ^-30 means that the region 10-30 nucleotides upstream of transcription start were deleted and the transcription rate was reduced to 0%.

Which mutant represents the deletion of a silencer?

Mutant	Deletion Region	% Transcription
Wild Type	None	100%
A	-10 — -30	0%
B	-30 — -100	50%
C	-500 — -700	100%
D	-700 —  -900	45%
E	-900 — -1100	30%
F	-1100 — -1300	100%
G	-1300 — -1500	150%

	a.	A
	b.	G
	c.	D
	d.	B
	e.	C

Answer 1

Question 1

Answer: Chromatin consists of DNA wrapped around protein. In highly condensed chromatin, the DNA is tightly wrapped around histone proteins and hence genes are not accessible for various proteins involved in their expression. During transcription, the DNA is relaxed by a process known as chromatin acetylation that involves addition of negatively charged acetyl groups to the lysine residues of the histone proteins. This leads to expression of genes. Hence, option e is the correct answer.

Removal of nucleotides and hydrolysis of DNA molecules damages the DNA. DNA coiling around the histone protein 1 will not relax the DNA. Deacetylase enzyme removes acetyl enzymes from the histone proteins, leading condensation of the DNA around histones. Hence, options a, b, c and d are incorrect.

Question 2

Answer: Alternative splicing is responsible synthesis of large number of protein in human cells as compared to small number of protein coding genes. Alternative splicing is a post-transcriptional modification of mRNA that involves fusion of exons in different combinations from a single gene to produce different proteins. Hence,option a is the correct answer.

Enhancers regulate the gene expression. miRNA are non-coding RNA molecules. Protein degradation degrades the proteins. Operons are found in bacteria that contain clusters of genes that controlled by operator. Hence, options b, c, d and e are incorrect.