Control of Gene Expression

Question 1

If all cells from the same organism contain the same DNA, how can they be so different?

Answer 1

Via Gene Expression; Different cell types produces sets of protein

Question 2

Why do cell differentiation arise?

Answer 2

Because cells make and accumulate different sets
of RNA and protein molecules: that is, they express different genes.

Question 3

Describe the cloning experiment that proves why different cell types contain the same DNA

Answer 3

1. Nucleus is taken out from a skin cell in an adult frog
2. The nucleus was injected into a frog egg with an empty nucleus
3. Tadpole continued to develop

Question 4

Why is the regulation of transcription paramount?

Answer 4

To ensure that no unnecessary intermediates are synthesized.

Question 5

What is the significant of having a regulatory DNA sequence to where the RNA polymerase initaite?

Answer 5

control transcription initiation; switch the gene on or off

Question 6

What must DNA sequence require to regulate transcription?

Answer 6

Transcription regulator

Question 7

What does transcription regulator do?

Answer 7

Act as a switch to control transcription

Question 8

Why is the major grooves of a DNA important for transcription?

Answer 8

Transcripter regulatory protein can interact with the genetic information at the major groove

Question 9

What is an operon?

Answer 9

Cluster of genes that are transcribed together to give a single messenger RNA

Question 10

What happens to the operon when tryptophan concentration is low in bacteria?

Answer 10

The operon is transcribed, making RNA that synthesize the amino acids

Question 11

What does transcription regulator do to prevent transcription?

Answer 11

It binds to the operator on the promoter which prevents access of RNA polymerase to the promoter, preventing transcription.

Question 12

What happens to the genes when tryptophan is low?

Answer 12

RNA polymerase binds to the promoter and transcribes the five genes of the tryptophan operon; operon is on and can be transcribed

Question 13

What happens to the genes when tryptophan is high?

Answer 13

Repressor protein becomes active and binds to the operator where it blocks the binding of RNA polymerase to the promote; operon is off and cannot be transcribed

Question 14

What does activator protein do?

Answer 14

bind to a nearby regulatory sequence and make contact with the RNA polymerase, helping it to initiate transcription

Question 15

Why might an activator protein be important for transcription?

Answer 15

the promoter may fails to initiate transcription efficiently.

Question 16

What does lac operon do?

Answer 16

Encodes proteins required to import and
digest the disaccharide lactose. I

Question 17

When would a lac operon shut off?

Answer 17

In the absence of lactose

Question 18

When is cAMP activated?

Answer 18

In the absence of lactose

Question 19

In the absence of lactose, which is activated/deactivated?

Answer 19

Lac operon is deactivated
cAMP is activated

Question 20

When is lac operon only activated?

Answer 20

In the presence of lactose
In the absent of glucose

Question 21

How can gene activation at a distance in eukaryotes?

Answer 21

Because DNA can loop, the activator protein can come in contact with the transcription initiation complex which may affect transcription rate

Question 22

How does gene affecting local chromatin structure regulate transcription via chromatin remodeling complex?

Answer 22

Render the nucleosomes more accessible to other proteins in the cell. TATA box may be exposed more, promoting transcription

Question 23

What is combinatorial control?

Answer 23

Multiple DNA-binding proteins can be involved in gene
regulation

Question 24

Eukaryotic cell uses a committee of transcription regulators to control each of its genes, how can it rapidly and decisively switch whole groups of genes on or off?

Answer 24

A single transcription regulator can be decisive in
switching any particular gene on or off by completing the combination needed to activate or repress a gene; the same protein can complete/regulate the combination for several different genes.

Question 25

What results in cell differentiation?

Answer 25

Combinations of transcription regulators resulting in gene expression diversity

Question 26

What is cell memory?

Answer 26

The patterns of gene expression responsible for that identity must be “remembered” and passed on to its
daughter cells through all subsequent cell divisions

Question 27

What are some post-transcriptional control?

Answer 27

RNA splicing

RNA degradation recognition sequences

Translation initiation blockers

Post-translational modification of proteins

Question 28

What regulates the controls of post transcription

Answer 28

micro RNAs
small interfering RNAs
long non-coding RNAs

Question 29

How does cell ensure that their daughter cell remember what kind of cells they should be?

Answer 29

positive feedback loop

Question 30

What is positive feedback loop

Answer 30

master transcription regulator activates transcription of its own gene, in addition to that of other cell-type specific genes.