Lecture 11 Prokaryotic Gene Regulation Flashcards
What is the Lac operon
Cluster of genes that code for beta galactosidase, permease and acetylase. 3 structural genes, Laz Z,Lac Y, Lac A. 1 upstream gene Lac ?/
What do the cluster of genes in the TRP operon do
they encode gees for the amino acid tryptophan
What are the two types of operon
- Inducible
- Repressible
In which organisms are operons typically found
Prokaryotes
What type of messenger RNA molecule is produced from an operon
Polycistronic mRNA
What is the result/phenotype of the Lac I- mutation
- Lac I- mutation produces a faulty repressor molecule that cannot bind to the operator.
- Lac operon is no longer inducible by lactose.
- Beta galactosidase is continually expressed as lac operon is permanently switched on.
- Lac I- mutation results in a permanently switched on ac operon, where Beta galactosidase is constantly expressed, independant of lactose concentration. It is known as a constitutive mutation.
What is the result/phenotype of the Lac O c mutation
- Lac O c mutation is a mutation in the operator region.
- ## It is a cis acting muation
Define cis-acting element
- Regulatory sequences that can only regulate DNA directly next to it/adjacent to it
- Cis acting elements include promoters/enhancers/ silencers.
Define trans-acting factor
- Transcription protein factors usually
- Trans acting factors can regulare DNA sequences anywhere.
What is meant by the term constitutive mutation
This is a mutation that results in the operon being permanently switched on.
Give an example of a constitutive mutation
the Lac I- mutation.
What is meant by trans acting mutation, and give an example
- Lac I- mutation
- This is a mutation in a trans acting factor - the Lac Repressor molecule.
What is meant by a cis acting mutation and give an example
- Lac O c mutation
- This is a mutation in a cis acting element, the operator region of the lac operon
Explain the concept of catabolite repression
Phenomenon where the presence of glucose will inhibit beta galctosidase production, as bacteria preferentially metabolize glucose over lactose. In high glucose (and lactose) environments, the RNA polymerase is unable to bind to the DNA and therefore the lac genes are not transcribed.
Explain what happens to the lac operon, in a high glucose environment
- High gluose means low levels of cyclic AMP
- low cyclic AMP means little/no CRP can bind to RNA polymerase.
- Without CRP, RNA polymerase cannot bind to the DNA/promoter of lac operon
- Therefore lac genes are not transcribed.
Explain what happens to the lac operon in a low glucose environment
- Low glucose means high levels of cAMP
- So cAMP can bind CRP
- This means CRP can bind to the RNA polymerase/can be used by RNA polymerase to bind to the lac promoter
- RNA polymerase binds and lac genes are transcribed., so beta galactosidase genes are produced, lactose can be metabolized now instead of glucose.
Which source of energy is preferred by bacteria
glucose, always!
What is CRP, what does it do and which molecule does it require
CRP = Catabolite repressor protein. Sometimes known as CAP, catabolite activator protein.
What happens to the trp operon in the presence of Tryptophan
When tryptophan is present, it binds to the repressor molecule, and together they bind to the trp operator. This blocks RNA polymerase from transcribing the 5 trp genes.
What happens to the trp operon in the absence of Tryptophan
When tryptophan is absent, the repressor molecule dimers are in their inactive form, and cannot bind to the DNA operator. Thus the operon is not blocked by repressor and the trp genes are transcribed, so tryptohphan is produced.
How many structural genes are encoded by the trp operon
5
Give an example of a repressible operon
The TRP operon. TRP acts as a co-repressor by binding to the trp repressor molecule
What is IPTG
a synthetic inducer for the lac operon, but is not a substrate like lactose. IPTG can be used to induce Beta galactosidase production. (and not be broken down by it too) Used in synthetic biology experiments.
Explain what an Operon is
A cluster of genes encoded for by a single promoter. Typically found in prokaryotes, very rare in humans and eukaryotes.
