Regulation of Gene Expression

Question 1

Specific Transcription Factors

What are the 2?

Answer 1

Activators and Repressors

Question 2

What makes cell types different if not a different genome?

Answer 2

Differential gene expression

Question 3

Chromatin

Answer 3

A complex of DNA and protein, and is found in the nucleus of eukaryotic cells

Question 4

Histones

Answer 4

Histones are proteins that are responsible for the first level of DNA packing in chromatin

Most chromatin is loosely packed during interphase and condenses before mitosis

Question 5

Euchromatin? Heterochromatin?

Answer 5

Euchromatin: Loosely packed chromatin
Heterochromatin: Highly condensed chromatin

Dense packing of heterochromatin inhibits gene expression

Question 6

When are centromeres and telomeres highly condensed into heterochromatin?

Answer 6

Interphase

Question 7

Histone Acetylation

Answer 7

This is when acetyl groups are attached to positively charged lysine’s in histone tails, loosening chromatin structure, promoting initiation of transcription.

Question 8

DNA Methylation

-CH3 group

Answer 8

• Enzymes methylate the DNA itself on certain bases, inhibiting expression of genes
• Underlies genomic Imprinting
• Blocks RNA polymerase from promoter

Question 9

Genomic Imprinting

Answer 9

• Inactive chromosomes are methylated
• Permanently regulates maternal or paternal alleles at the start of development

Question 10

Epigenetic Inheritance

“above” DNA

Answer 10

A change in gene expression that is NOT due to a change in the DNA sequence, which is passed along to future generations.

Question 11

Enhancer

Answer 11

Group of Distal Control Elements

Question 12

Proximal Control elements

Answer 12

Control elements found close to the promoter sequence

Question 13

Activator

What are the two domains?

Answer 13

A protein that binds to an enhancer and stimulates transcription of a gene.
The two domains are:
1. one that binds DNA
2. another that activates transcription

Bound activators facilitate a sequence of protein-protein interactions resulting in transcription

Question 14

Repressor

Answer 14

A specific transcription factor that blocks transcription of a gene
1. Binds to enhancer and blocks activator
2. Directly interferes with activator

Question 15

What are the steps of the protein-protein interaction that results from activator binding?

Answer 15

1. Activator proteins bind to enhancer
2. DNA-bending protein binds and transcription factors bind to promoter (with mediator proteins)
3. Active Transcription Initiation Complex forms

Question 16

How does the cell know whether to make albumin (for liver cells) or crystallin (for lens cells)?

Answer 16

• Each respective gene has a unique enhancer (control elements) that only binds specific activators
• Whatever activators are available directly correlate to the protein produced

Question 17

What are the three ways genes can be regulated in the RNA processing stage?

What happens at each step?

Answer 17

1. Alternative RNA splicing: The cell decides which genes to be treated as introns/exons
2. mRNA degradation
   * Initiated by shortening of the polyA tail
   * Removal of 5’ cap
   * Nuclease enzymes chew up mRNA
   * half life in bacteria is much shorter than in Eukaryotes
3. Initiation of translation
   * can be blocked by regulatory proteins (blocks ribosome)
   * Regulator proteins bind 5’ UTR

Question 18

How does protein processing and degradation regulate gene expression?

Answer 18

• Cleavage and Addition of chemical groups can affect gene expression
• Proteasomes can degrade protein complexes tagged with ubiquitin (such as cyclin which needs to be short lived)

Cleavage of initial insulin polypeptide/Addition or removal of phosphate groups can determine functionality of proteins