Topic 23: Regulation of Gene Expression - Prokaryotes Flashcards
Describe a general operon. What is a polycistronic mRNA?
General operon is a cluster of cells that all work together to do the same thing.
Describe the regulation of the Lac Operon. What is happening at the Lac Operon when Lactose is present and what is happening when lactose is absent?
The Lac Operon regulation is an inducible Operon. The operon is this process is usually off. The Lac operon represent a catabolic process where the cell looks to break down lactose.
When lactose is present the the operon is on. This happens as the lactose acts as an inducer and binds to the repressor, which prevents it from binding to the operator allowing it to be on.
When lactose is absent the operon is off. If lactose is absent there is nothing to bind to the repressor and the repressor binds to the operator. preventing it to continue turning it off.
Describe how glucose concentrations affect regulation of the lac operon. What will happen to transcription in varying conditions?
Glucose is widely preferred by the E.coli over lactose. The activator CAP job is to increase the Transcription rate of a gene.
High level of glucose - there are low levels of amp, which prevent CAP from activating meaning there is a low Transcription rate.
Low levels of Glucose- means high amounts of CAP being activated by amp and higher rate of Transcription.
Contrast inducible (lac) and repressible (trp) operons.
Lac operons (inducible): Repressible Operons:
- Catabolic - break Down - Anabolic (BUILD)
- Operon mainly are off - Operons mainly ON
- Involves lactose - Ex: Tryptophan
- glucose concentrations affect lac operons - co-repressors (triphtophan) bind to a r(lactose)= inducer repressor protein.
Summary:
Prokaryotes gene expression respond to environmental changes. As we know in prokaryotes both transcription and translation occur at the same time in the same location.
A mechanism that helps control gene expression is the operon model.
The operon model is a basic way to control gene expression, to help have different functions and roles with the same genome. ex: muscle cells, eye cells, etc.
An operon is a cluster of cells that all work to do the same thing.
In the operon model we will have a promoter where RNA polymerase binds to begin transcription, then an operator which is the on and off button (DNA sequence) for the process to continue, then we have the genes or enzymes that work together. And far from the promoter we find a regulator, which binds to the operator to to prevent the enzymes from being made.
Example of a real operons are repressible operon(anabolic), which are capable of being repressed. Ex: tryptophin acts as a co-repressor and binds to a repressor protein or the repressor can be inactive as well when the amino acid is not present.
