Lecture 17- Prokaryotic Transcriptional Control Flashcards
What are operons?
A sequence of genes under the control of a single promoter, which function with either positive or negative control.
What are the regions of an operon and their functions?
There is the Regulatory gene, which makes the activator or the repressor. Next is the Promoter, where RNA-polymerase binds. Then there is the Operator, where the repressor or activator binds, and then there are the genes.
What is negative control?
When the regulatory gene makes repressors. This means that the operon is always on, unless there is a repressor bound to the operator stopping the RNA polymerase.
What is positive control?
When the regulatory gene makes activators. This means that the operon is always off, unless there is an activator bound to the operator allowing the RNA polymerase to work.
What is polycistronic mRNA?
When mRNA molecules can produce multiple proteins in prokaryotes. In eukaryotes, only one protein can be produced per mRNA molecule.
What is induction?
When the presence of chemicals in the environment deactivate the repressor for negative control operons.
Explain the lac operon.
This operon synthesizes proteins that are responsible for the metabolism of lactose. This operon is negatively controlled and induced by the presence of lactose. If there is a lot of lactose in the environment, the cell will want to produce the proteins required to metabolize it.
What is repression?
When the presence of chemicals in the environment activates a repressor, which will stop protein synthesis. This happens for negative control operons.
Explain the trp operon.
This operon codes for a protein that synthesizes tryptophan. When there is a lot of tryptophan in the environment, the repressor is activated, and so the production of the protein stops.
Explain the more detailed lac operon.
When a lot of lactose is present, the repressor will be repressed, allowing for the synthesis of the proteins responsible for processing the lactose. But this only happens when glucose is low and cAMP is high, as this inducer binds to the CAP activator protein. When glucose is high, there is no cAMP to bind to CAP, and so the operon does not function as well, as the cell will use glucose instead of lactose as energy currency.
