Regulation Of Gene Expression Flashcards
(24 cards)
What is gene expression (gene regulation)?
Mechanisms which cells use to turn the processes of transcription and translation on and off.
Why is gene regulation important?
It allows an organism to express certain proteins only when they are needed.
Prevents waste of materials and energy.
A classic example of a gene regulation system is the lactose operon. What does this illustrate?
Enzymes involved in lactose metabolism are expressed by E.coli only in the presence of lactose and absence of glucose.
What is an operon?
A group of genes that work together under the control of a single promoter.
What are the results of genes being under an operon?
- They can be translated and transcribed together.
- Protein products may have related functions.
Where is gene expression more complex? In eukaryotes or prokaryotes?
Eukaryotes
Mention some levels at which gene expression takes place in eukaryotes?
- transcription of DNA to RNA
- translation of mRNA into a polypeptide chain
- cell differentiation
- growth and development
- post translational modification of the polypeptide chain
- post translational modification of RNA to primary transcripts
What is up-regulation?
Process where an internal or external sign results in increased expression of one or more genes resulting in increased protein synthesis.
What is down regulation?
Process resulting in decreased gene and corresponding protein expression.
What is an inducible system?
A system normally turned off except in the presence of an induced molecule which turns it on and allows gene expression to take place.
What is a repressible system?
A system usually switched on except in the presence of a co-repressor molecule that suppresses gene expression.
Who discovered the lac operation?
Jacob and Monod
What does the lac operation consist of?
Three structural genes controlled by a regulator gene.
Name three sequences in which the lac operation works in conjunction with?
- operator sequence
- promoter sequence
- terminator sequence
The lac operon has three structural genes.
What is that is the function of:
lacZ gene
Encodes enzyme B-galactosidase.
Breaks down disaccharide lactose into monosaccharides glucose and galactose
LacY gene?
Encodes membrane bound protein B-galactoside permease (pumps lactose into the cell)
LacA
Gene which encodes enzyme B-galactoside transacetylase (modified lactose)
Why is the lac operon needed?
Efficient transport and metabolism of lactose in E. Coli.
Lactose can be used as energy in absence of glucose. What must be done first?
Produce enzymes that are needed to mobilise and digest the lactose called B-galactoside.
Lac operon ensures that the cell uses energy in producing the three enzymes only when necessary.how does it do this?
Using the repressor molecule, which stops the three enzymes in the absence of lactose.
Repressor molecule has two active sights. What happens at these and name the molecules involved.
Inducer molecule (lactose) can act or repressor (glucose)
How does whether the operator gene is on or off affect things?
When on, structural genes carry out the transcription of mRNA which is then translated to polypeptides. When off, no mRNA is transcribed.
What happens when E. Coli is grown on a glucose medium?
Regulator gene produces a repressor molecule which binds to glucose which is a co-repressor. Activates repressor molecule and causes it to bind to the operator gene and switches off whole system.
What causes negative feedback in end product inhibition or repression?
Enzymes for glucose production (from lactose breakdown) are not synthesised because glucose is already there.
