Gene Regulation Flashcards
What is Gene expression
The process by which the information encoded in genes is used to direct the assembly of a protein molecule
Why is gene regulation important
If all genes were switched on at all times the metabolic demand would be too great
Where is prokaryotic gene expression primarily controlled
During transcription
What are housekeeping genes
Expressed at all times during a cells life cycle
Usually essential genes
Often used as reference genes during experiments
What are the properties of regulated genes
Expression varies depending on internal or external circumstances
Often a response to an environmental genes
Can be reduced or repressed
How are genes regulated during the initiation of transcription
Altering the specificity of RNA polymerase by using different sigma factors
Preventing RNA polymerase from accessing the promoter
Using activating transcription factors to enhance the promoters affinity for RNA polymerase
What is the positive control of gene expression
The product of the regulator gene is required to turn on the other genes
What is the negative control of gene expression
The product of the regulator gene turns off the expression of other genes
What are effector molecules
Small molecules that can bind to repressors or activators and cause a conformational change
What is an Operon
A complete genetic unit containing a cluster of genes that all share a promoter and regulator sequences
An Operon will often contain all the genes that code for all the enzymes for a particular pathway bas well as the genes that regulate them
What subunit of RNA polymerase is responsible for its specificity
The sigma factor
They bind to the promoter region of region of DNA
What are the three genes that code for lactose metabolism in the lac Operon
Beta-galactosidase (lacZ): cleaves lactose to yield glucose and galactose
Lactose permease (lacY): transports lactose into the cell
Thiogalactoside transacetylase (lacA): transfers an acetyl group from acetyl-CoA to beta-galactosidase
What are the regulator genes for the lac Operon
lacI: encodes for a repressor that binds to DNA just downstream of the promoter which blocks RNA polymerase from biding
What is allolactose
Allolactose is an induced that binds to the repressor protein in the lac Operon. This cause the repressor to dissociate, allowing the lacZ, lacY and lacA genes to be expressed
What is CAP
CAP is an activator protein in the lac Operon. It binds to a CAP site just upstream of the promoter and greatly increases gene expression
CAP can only bind to a CAP site when cAMP is bound to it
This is an example of positive regulation
How does glucose regulate cAMP
cAMP is synthesised by an enzyme called adenyl cyclase
Glucose inhibits adenyl cyclase
When glucose levels are high, cAMP levels are low
This means that expression of the lac Operon is low due to low cAMP levels
What is the trp Operon
An Operon that contains the genes that code for the biosynthesis of tryptophan
How is the trp Operon regulated
Tryptophan activates the repressor protein that turns off the trp Operon. When tryptophan levels are high, the Operon turns off, when tryptophan levels are low, the Operon turns off to produce more
What is transcription attenuation
After transcription begins it can be halted by an attenuator sequence. It is on the 5’ region of a leader sequence
In the trp Operon the attenuation sequence forms a hairpin structure
Attenuation is a translation dependant modulation of transcription
What are the uses of lac genes in bioengineering
Converting a colourless substrate blue
Use as reporter genes
Blue/white screening
What does polycystromic mean
An mRNA molecule that yields two or more proteins
