Control of Gene Expression Flashcards
where is gene expression regulated?
It is regulated at transcription
How does gene expression work?
Each different type of cell only uses some of the genes in its total repertoire
What is gene expression?
The expression of a different collection of genes in each cell type which causes variation and differentiation in cells
What are gene regulatory proteins?
Proteins specialised for switching genes on and off
What does the promoter region of a gene do?
It attracts RNA polymerase and correctly orientates the enzyme to begin its task of making an RNA copy of a gene
What do gene regulatory proteins bind to?
Regulatory DNA sequences
What acts as a switch to control transcription?
2
A combination of regulatory DNA sequence and
Gene regulatory proteins
At what level is the expression of eukaryotic genes controlled?
Controlled primarily at the level of initiation of transcription
What controls gene expression in eukaryotes?
The combined actions of multiple different transcriptional regulatory proteins
Bacteria regulate the expression of their genes according to what?
According to the food sources available in the environment
Why do bacteria adapt so quickly?
Operons
What is an operon?
A set of adjacent genes in a bacterial genome, transcribed from a single promoter into a single mRNA
What is the function of operons?
They group related genes under a common control mechanism which allows bacteria to rapidly adapt to changes in the environment
What are the two examples of operons in E.coli?
Trytophan Operon
Lac Operon
Write a note on the trytophan operon
4
5 genes which encode for enzyme which manufacture trytophan
These genes are arranged in a cluster on the genome (form an operon)
Genes transcribed from one promoter as 1 long mRNA molecule from which 5 proteins are translated
This operon isn’t needed if bacteria can get trytophan from their environment so it’s shut off
What is the trytophan operator?
2
A short DNA sequence within the promoter, upstream of the trytophan operon
Which is recognised by a gene regulatory protein (tryptophan repressor)
What is the trytophan repressor?
2
A protein that binds to the tryptophan operator, blocking the access of RNA polymerase to the promoter
Shuts off the operon
What is required of the tryptophan repressor before it can bind to the operator and stop the operon from being polymerised?
(2)
The repressor must bind to the amino acid tryptophan
This binding causes a subtle change in 3D structure which allows it to bind to the operator DNA
Define a repressor protein.
A protein that switches genes off or represses them
Define an activator protein
A protein that switches genes on or activates them
Write a note on the lac operon
3
Operon that encodes proteins required to import and digest lactose
Consists of 3 genes: lacZ, lacY and lacA
All genes under control of 1 promoter
Does the lac operon require induction to be expressed
No it doesn’t
What are the four lac genes?
lac Y
lac Z
lac A
lac l
What does the lac Y gene code for?
Codes for lactose permease
What does lactose permease do?
It transports lactose into the cell
What does the lac Z and lac A genes code for?
They code for the enzymes b-galactosidase and transacetylase
What does b-galactosidase and transacetylase do?
They split lactose into galactose and glucose
What does the lac l gene do?
2
It’s located outside the operon
It codes for a repressor protein which can switch off the lac operon by binding to the operator sequence
Where is the lac operon operator sequence found?
2
Lies within the promoter for lactose operon
Just upstream of the operon genes
What is lactose split into?
2
Glucose
Galactose
What is an intermediate between lactose and glucose and galactose?
Allolactose
What is allolactose?
An isomer of lactose
What does allolactose do?
2
It binds to the lac operon repressor protein - causing a change in conformation
This prevents the repressor protein from working and binding to the operator sequence
