Symes Control of Gene Expression

Question 1

When is the Lac operon switched on?

Answer 1

If no Glucose is present

Question 2

Z gene lac operon

Answer 2

ß-galactosidase
- converts lactose into glucose and galactose

Question 3

Y gene lac operon

Answer 3

Galactoside permease
- brings lactose into cell

Question 4

a gene lac operon

Answer 4

Thiogalactoside transacetylase, don’t need to know what it does

Question 5

I gene lac operon

Answer 5

Encodes repressor

Question 6

o gene lac operon

Answer 6

RNA Polymerase binding site

Question 7

CRP gene lac operon

Answer 7

cAMP receptor protein binding site

Question 8

How does glucose affect the presence of cAMP in the cell and if it will bind CRP

Answer 8

High glucose = low cAMP, low CRP
Low glucose = high cAMP, high CRP

Question 9

Ratio of proteins generated from genes Z, Y and A in the lac operon

Answer 9

10:5:2

Question 10

If there is only Glucose present, what is occurring with the lac operon?

Answer 10

The I gene produces the repressor protein which binds to O to prevent RNA Pol from binding

Question 11

Go through what happens in the cell if Lactose is present

Answer 11

1) Permease brings lactose into the cell
2) ß-galactosidase breaks down lactose and convert some into allolactose
3) Allolactose binds the repressor allowing transcription to occur
4) cAMP binds CRP, causing it to bind the CRP region
5) CRP binding stimulates RNA Pol to bind promoter, high levels of transcription

Question 12

What is CRP

Answer 12

Protein which stimulates RNA Pol to bind the promoter to increase transcription to a high level

Question 13

Helix-turn-helix motif

Answer 13

Present in almost all prokaryotic and in some eukaryotic TFs
- recognition helix, turn, stabilization helix
- stab helix binds major groove
- dimer

Question 14

What do we need to know about the ß-pleated sheet motif?

Answer 14

it exists

Question 15

How is the Zinc finger formed?

Answer 15

The presence of Zinc causes interactions which forms the finger (which is an alpha helix)

Question 16

What is the structure of the Leucine Zipper motif?

Answer 16

A dimer of basic regions binds the DNA, while two alpha helices create the zipper portion
- Leucines sticking out of the alpha helices interact with each other to form the zipper

Question 17

What is the bZIP motif?

Answer 17

Same as Leucine zipper, but Leucine is replaced with a different hydrophobic amino acid

Question 18

What is the basic helix-loop-helix motif?

Answer 18

A dimer which binds the alpha helix major groove. Its structure contains a basic alpha helix DNA binding region. It has a zipper, but it includes a non-helical loop in each monomer.

Question 19

What is the importance of heterodimers in TF motifs?

Answer 19

They allow for interactions with regulatory proteins

Question 20

How do CpG islands inhibit transcription?

Answer 20

Their methylation recruits CpG Island Binding Proteins such as histone deacetylases

Question 21

What is the Imprinting concept?

Answer 21

Once copy of the gene received from the sperm or egg is methylated. If the methylation flips to the other copy, that can lead to disease

Question 22

Prader-Willi

Answer 22

obesity, short stature, hypogonadism
- 75% due to loss of non-methylated gene
- 25% due to trisomy

trisomy is extra imprinted gene, loss of non-imprinted gene

Question 23

Angelmann’s syndrome

Answer 23

Epilepsy, tremors, perpetually smiling
- 75% loss of imprinted
- 25% trisomy

trisomy is extra imprinted gene, loss of non-imprinted gene

Question 24

Effect of absent T3 on Thyroid receptor

Answer 24

The lack of T3 causes TR and RXR to bind the corepressor complex, activating its HDAC domain. This then prevents transcription

RXR: Retinoid X Receptor

Question 25

Effect of present T3 on thyroid receptor

Answer 25

The T3 binds TR, the corepressor complex leaves and the coactivator which has an HAT domain binds, activating transcription

HAT: Histone Acetyltransferase

Question 26

Which histone modification causes transcriptional repression?

Answer 26

Methylation of Lysine depending on location

histone tail modifications usually support transcription

Question 27

What is the structure of CRP?

Answer 27

• helix-turn-helix motif
• dimer

Question 28

Where does the Zinc finger sit?

Answer 28

DNA major groove

Question 29

Why does the Zinc finger not need to dimerize?

Answer 29

The presence of multiple motifs causes multiple interactions (ie. fingers) which negates the need for dimerization

Question 30

Prader-Willi and Angelmann’s syndrome are a result of a malfunction in which methylation process?

Answer 30

Imprinting

Question 31

What is Igf-2 methylation an example of?

Answer 31

Imprinting of a gene can actually activate transcription, instead of inhibiting it. The methylation prevents binding of a repressor to allow transcription