GENE CONTROL

Question 1

When is a gene expressed

Answer 1

When it is transcribed into mRNA which is translated to a protein

Question 2

GENE CONTROL IN PROKARYOTES

Question 3

What is B-galactosidase use for

Answer 3

enzyme used in bacteria to hydrolyses lactose to glucose and galactose which is then absorbed as an energy source.

Question 4

What is permease used for

Answer 4

Allows lactose to enter the cell

Question 5

What is transacetylase used for

Answer 5

Transfers an acetyl group from acetyl-CoA

Question 6

What does a structural gene do

Answer 6

Codes for a protein that is used by the cell

Question 7

What do regulatory genes do

Answer 7

Control the expression of other genes

Question 8

Where are structural and regulatory genes found

Answer 8

Together in groups called OPERONs

Question 9

What operon is responsible for the production of B-galactosidase (lactase)

Answer 9

Lac OPERON

Question 10

What controls whether genes are switched on or off in this process
How is the enzyme altered

Answer 10

The concentration of lactose in the medium in which the bacteria grows.
The enzyme is altered by switching the transcription of the B-galactosidase gene on or off.

Question 11

Sequence of events when there is no lactose present

Answer 11

• The regulatory gene codes for a protein - repressor
• The repressor binds to the operator region, close to the gene for B-galactosidase
• Because the repressor is attached to the operator, RNA polymerase cannot bind to DNA at the promoter region.
• As a result, there is no transcription of the three structural genes.

Question 12

Sequence of events when lactose is present

Answer 12

• Lactose is taken up by the bacterium
• Lactose binds to the repressor protein, distorting its shape and preventing it from binding to DNA at the operator site.
• Transcription is no longer inhibited, RNA polymerase can bind to the promoter and messenger RNA is produced from the three structural genes.
• The genes have been switched on and are transcribed together.
• The bacterium can now absorb and break down lactose into glucose and galactose for energy.

Question 13

Why is process useful

Answer 13

Avoids wasting energy and materials

Question 14

What type of enzyme is B-galactosidase
And what does that mean

Answer 14

It is an inducible enzyme
It is synthesised only when the substrate is present

Question 15

What is the other type of enzyme
What does that mean

Answer 15

Repressible enzyme
Binding of the effector molecule to the repressor helps it to bing to the operator. So the repressor attached to the operator region, which stops transcription.

Question 16

TRANSCRIPTION FACTORS IN EUKARYOTES

Question 17

What controls the expression of genes in eukaryotes

Answer 17

Transcription factors

Question 18

What is a transcription factor
What is its role

Answer 18

It is a protein that binds to DNA and affects whether or not a gene is transcribed
Its role is to make sure that genes are expressed in the correct cell at the correct time and to the right amount

Question 19

3 examples of transcription factors working

Answer 19

Responsible for the determination of sex in mammals

General transcription factors are necessary for transcription to occur. Forming part of the protein complex that binds to the promoter region of the gene concerned

Control of gibberellin production

Question 20

Process of gibberellin production

Answer 20

Gibberellin has this effect by causing the breakdown of DELLA proteins.
A molecule known as a DELLA protein is a repressor protein.

DELLA proteins normally inhibit the binding of a transcription factor ~ phytochrome-interacting protein (PIF), to a gene promoter.

Transcription of the gene can then take place, resulting in an increase in amylase production.