CONTROL OF GENE EXPRESSION IN EUKARYOTES (LECTURE 9)

Question 1

What is cell differentiation?

Answer 1

When cells diverge in structure and function during development.

Question 2

How do cells differentiate into so many different cell types?

Answer 2

Specific genes are turned on and off by specific transcription factors.

Question 3

What are the two types of eukaryotic gene expression control?

Answer 3

Transcriptional control and post-transcriptional control.

Question 4

What elements participate in transcriptional control?

Answer 4

Transcription factors (activators and repressors).

Question 5

What elements participate in post-transcriptional control? (5)

Answer 5

RNA processing, mRNA degradation, translational control, protein processing and protein degradation.

Question 6

Describe the mechanism of transcriptional control.

Answer 6

Eukaryotic RNA polymerase cannot recognize a promoter without specific transcription factors.

Question 7

Why can some RNA polymerase recognize some promoters and not others right next to them?

Answer 7

Because the required transcription factors are specific to certain genes.

Question 8

Where do transcription factors bind?

Answer 8

These bind to non-coding regions of DNA called control elements.

Question 9

What are the two types of transcription factors and how do they differ?

Answer 9

Activators enhance transcription and inhibitors inhibit transcription.

Question 10

What are the two types of control elements (DNA sites where transcription factors bind)?

Answer 10

Control elements can be proximal or distal.

Question 11

Describe proximal control elements.

Answer 11

These are close to or located within the promoter.

Question 12

Describe distal control elements. (3)

Answer 12

These can be: upstream or downstream of the promoter; within introns; thousands of nucleotides away form the promoter.

Question 13

What are enhancers?

Answer 13

An enhancer is a group of distal control elements.

Question 14

Do the DNA of all cells have the same control elements?

Answer 14

Yes.

Question 15

If the DNA of all cells have the same control elements, how can these cells be so different?

Answer 15

The cells have different transcription factors.

Question 16

What steps are involved leading up to the initiation of transcription? (3)

Answer 16

(1) Activators (specific transcription factors) bind to control elements in enhancers. (2) DNA bends to bring activators to the promoter. Activators will interact with general transcription factors and mediator proteins at the promoter. (3) RNA polymerase will bind to the promoter and initiate transcription.

Question 17

Control elements help to ____ gene expression.

Answer 17

Control elements help to coordinate gene expression.

Question 18

Genes that code for the enzymes of the same metabolic pathway are located where in eukaryotes?

Answer 18

Genes that code for the enzymes of the same metabolic pathway are located on different chromosomes (unlike operons in prokaryotes).

Question 19

How do control elements help coordinate gene expression when the genes involved in the same metabolic pathway are located on different chromosomes?

Answer 19

Each gene in the pathway has identical control elements recognized by a single type of transcription factor.

Question 20

Name two examples of physically distant genes being turned on at the same time.

Answer 20

This occurs in the heat shock response and for steroid hormones.

Question 21

What do heat shock proteins do?

Answer 21

Heat shock proteins stabilize proteins and prevent them from being denatured (help them fold properly).

Question 22

Describe the heat shock response.

Answer 22

First there is a stress to the cells (such as increase in temperature). The same transcription factors then turn on all the heat shock protein genes.

Question 23

How come the same transcription factors can turn on all the heat shock proteins in a heat shock response?

Answer 23

Because the heat shock protein genes all have the same control elements.

Question 24

Provide 3 examples of steroid hormones.

Answer 24

Estrogen, testosterone, progesterone.

Question 25

Where do steroids bind to receptors? How do they get there?

Answer 25

Steroids cross the cell membrane by simple diffusion and bind to receptors within the cell.

Question 26

How does a steroid-receptor complex behave following the binding of a steroid to a receptor?

Answer 26

Steroid-receptor complex acts as a transcription factor that turns on a number of genes on different chromosomes (these genes have have the same control elements).

Question 27

In general, how will 3 genes of the same metabolic pathway be turned on at the same time?

Answer 27

Genes in the same metabolic pathway (or process) will contain the same control elements and thus can all be turned on by the same transcription factors.