Gene Expression 1 Flashcards
(29 cards)
What is gene expression?
The process that result in the production of functional protein
What controls gene expression?
Levels of transcription processing (splicing in eukaryotes) translation mRNA stability Protein stability
What is a transcription factor?
Proteins that bind to DNA and affect the transcription of genes located near where they bind
Why is gene expression control important?
Allows for organisms to be able to respond their their environment. For example, e coli prefers glucose, but must be able to use other sugars when they’re available.
What is an operon?
A prokaryotic system for organizing genes with related functions under the same transcriptional control.
What do genes on the same operon in prokaryotes do?
They are all synthesized on the same mRNA.
What does polycistronic mean?
mRNA’s containing multiple gene coding sequences
Describe the lactose operon
Consists of three linked structural genes that encode enzymes of lactose utilization, plus adjacent trajectory sites
What are the three enzymes of lactose operon?
–z, y and a– encode for beta-galactosidase, beta-galactoside permase and thiogalactoside transacetylase
Where does transcription of the lac operon commence near?
A promoter (lacP) before lacZ, and it transcribes a 5200 nucletoide mRNA, ending at a terminator beyond lacA.
What does regulation of the lac operon involve?
Three regions of DNA near the transcriptional start site. Move in the 5’ to 3’ direction, the CAP binding site, promoter, operator.
How is negative transcriptional regulation accomplished?
Through a protein known as the lac repressor.
What does the lac repressor do?
binds to the operator region, overlaps with the promoter and inhibits binding of RNA polymerase.
What does an inducer molecule do?
It binds to the lac repressor and changes its shape to reduce its ability to bind the operator, thus allows RNA polymerase to bind the promoter and start transcription.
What is the inducer molecule?
It is related to lactose and is known as allo-lactose. Only made when lactose is present.
What happens when the inducer molecule is not present?
The lac repressor binds tightly to the operator and inhibits transcription of the operon
What protein acts positively to help activate the lac operon?
CAP (also called CRP)
What does CAP do?
Binds to cAMP and causes a shape change in CAP that allows it to bind to the CAP binding site. This stimulates binding of RNA polymerase and transcription of the operon.
What regulates the trp operon of E Coli?
Transcription factors and by the phenomenon of attenuation
What does the trp repressor do?
bind to the trp operator sequence and inhibit transcription of the operon. ONLY CAN HAPPEN WHEN IT IS BOUND TO TRYPTOPHAN
What is attenuation
Regulatory mechanism for several E. coli operons.
How does attenuation occur?
a short leader sequence, which is a short open reading frame that contains codons for the amino acid in question
When does translation of the trp operon begin?
As soon as the AUG codon for the leader sequence is transcribed.
How many regions of mRNA for trp operon exist?
- 1 pairs with 2, 3 pairs with 4, 2 pairs with 3.
