GENE CONTROL Flashcards
When is a gene expressed
When it is transcribed into mRNA which is translated to a protein
GENE CONTROL IN PROKARYOTES
What is B-galactosidase use for
enzyme used in bacteria to hydrolyses lactose to glucose and galactose which is then absorbed as an energy source.
What is permease used for
Allows lactose to enter the cell
What is transacetylase used for
Transfers an acetyl group from acetyl-CoA
What does a structural gene do
Codes for a protein that is used by the cell
What do regulatory genes do
Control the expression of other genes
Where are structural and regulatory genes found
Together in groups called OPERONs
What operon is responsible for the production of B-galactosidase (lactase)
Lac OPERON
What controls whether genes are switched on or off in this process
How is the enzyme altered
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.
Sequence of events when there is no lactose present
• 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.
Sequence of events when lactose is present
• 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.
Why is process useful
Avoids wasting energy and materials
What type of enzyme is B-galactosidase
And what does that mean
It is an inducible enzyme
It is synthesised only when the substrate is present
What is the other type of enzyme
What does that mean
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.
TRANSCRIPTION FACTORS IN EUKARYOTES
What controls the expression of genes in eukaryotes
Transcription factors
What is a transcription factor
What is its role
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
3 examples of transcription factors working
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
Process of gibberellin production
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.
