MCB Lecture 21 Gene expression Flashcards
What is regulated gene expression?
The gene is only transcribed under specific conditions and signals
What is constitutive gene expression?
The gene is always on
This may be a housekeeping gene
What is negative gene regulation?
What molecule causes it?
This is when the rate of transcription is decreased
Repressors cause this
What is positive gene regulation?
What molecules causes it?
This is when the rate of transcription is increases
Activators cause this
What are the levels of regulation in gene expression?(3)
Transcriptional
Post transcriptional
Post translational
What is the role of ligand a in gene expression?
A ligand binds to an activator or repressor and changes the function of it
What is a major ligand in gene expression
Tryptophan
Describe the four ways that ligand a may change gene expression
Ligand binds to a repressor, causing it to bind to an operator. GENE OFF
Ligand binds to a repressor, inhibiting it from binding to the operator. GENE ON
Ligand binds to an activator, causing it to binding to an operator. GENE ON
Ligand binds to an activator, inhibiting it from binding to an operator. GENE OFF
What are the two regions in the prokaryotic promoter?
What happens at these two regions?
-35 and -10
The sigma subunit has two prongs which bind to these regions.
The RNA pol then binds forming the holo enzyme which is ready to transcribe
Transcription starts (sigma falls off)
Where does the sigma factor bind? What happens next?
To the -35 and -10 regions in the promoter
What is an operon?
How many promoters does it have?
This is a region of many genes that are under the control of one promoter
They are all transcribed into one mRNA, then into many proteins
Describe the mRNA produced from an operon and the proteins that result
Only one mRNA
Many proteins
Where is an operator located?
In between the -35 and -10 of a promoter
What is the function of an operator?
It binds activators and repressors,thus controlling transcription and gene expression
What is a cistron? Thus, what is a poly cistron?
A cistron is a gene in the operon
A poly cistron is the group of cistrons
What are cis acting elements?
Give an example of a cis acing element
These are regions of DNA that control the expression of a gene
Eg. Operator
What are trans acting elements?
Give examples
These are factors that are mobile and interact with regions of DNA, bringing about changes in transcription and this gene expression
Eg. Activator or repressor
How are cis and trans acting elements / factors differentiated?
If a cis acting element is moved, it will no longer function
This is not true for trans acting elements
Describe the nutrition of E. coli
Glucose is preferred
Lactose at a push
What is lactose broken down into, and what enzyme does this?
Broken down into galactose and glucose
Beta-galactosidase to break the beta-galactoside linkage
Describe the lac operon and does it have its own promoter?
Yes it does
O P Y Z A
What does lacP do?
This is the promoter for the operon
What does lac O do?
It is the operator for the operon
What does lac Z do?
Codes for beta galactosidase
