Gene Regulation Flashcards
U2L5
What is Regulation?
Regulation is essentially a mechanism which could increase, decrease, initiate or stop protein synthesis.
What’s the purpose of regulation?
It’s really just meant to prevent the cell from wasting energy.
What is an Operon?
An Operon is a self-regulating series of genes that work in harmony.
What does an Operon include?
An Operon includes a region of genes that are regulators of protein synthesis, but do not actually code for a protein.
These are called the promoter and operator regions.
What is the regulator region?
The regulator region is a portion of the DNA that codes for repressor proteins. These can repress/block RNA transcription.
It binds to the operator site so RNA Polymerase cannot run and copy the DNA strand.
What is the promoter region?
Same as always.
It’s a region on DNA that RNA polymerase binds to, to begin transcription.
What’s the operon hypothesis in a nutshell?
The hypothesis essentially states that not all genes need to be turned on all the time. Because of this, operons are a group of those genes that could be enabled or disabled.
The “operator” is in the promoter region of DNA,
and acts as a switch to determine if the gene is
transcribed (“on”) or not transcribed (“off”).
Different operons have different ways to control
whether or not a gene is on or off.
How does the Lac operon work?
Basically E-coli uses β-galactosidase to break down Lactose. Bacteria only produces it when lactose is present in order to avoid wasting energy. The production of this enzyme is controlled by a negative control system.
The gene for β-g is part of an operon (cluster of genes under the control of one promotor and one operator)
How is the repressor for B-g made?
RNA Polymerase makes RNA with the B-g gene. This gene gets made into a repressor protein. When Lactose is not present, this protein binds to the operator region on the DNA, essentially blocking the RNA from copying the lac operon.
What happens if Lactose is present.
If lactose is present, Lactose behaves as an inducer molecule. It binds to a site on the repressor which causes it to change shape and deactivate. When the repressor changes shapes, it can no longer bind to the operator region which makes the RNA Polymerase transcribe the operon and create B-g to break down the Lactose.
How does the Trp operon work?
For context, the regulator region always produces the Tryptophan repressor.
It acts as the direct opposite of how the lac operon works.
When no Trp is present, the repressor cannot bind to the operator region which allows for Trp to be produced.
When more Trp is produced, a molecule of Trp (which acts as a co-repressor) binds to the repressor protein. This causes the protein to change into the correct shape. The protein then binds to the operator region, causing the transcription of Tryptophan to stop.
How do Eukaryotic cells control gene production?
There are no operons in eukaryotic cells
Gene expression relies on DNA
promoters and transcription factors
(regulator proteins) which together
create an initiation complex.
Individual cell types basically add methyl groups to Cytosine in certain genes to silence them
How does post-transcriptional control work?
The cell can control the rate at which Pre-mRNA is produced into mRNA.
This can be done by preventing the 5’ cap from being added (which will degrade the mRNA strand). The 3’ cap can also not be added which will trap the strand in the nucleus and the strand will fall apart over time.
What’s Translational Control?
One the mRNA is in the cytoplasm; regulatory proteins can attach the mRNA which can prohibit the Ribosomes from attaching to the mRNA for translation.
What happens in post-translational control?
The polypeptide chain is modified chemically, or the cell varies its rate at which it becomes a functional protein (Chaperones with folding).
The polypeptide can also be degraded by the cell before folds into a functional protein.
