Lecture 14a Flashcards
What do regulatory transcription factors do?
They influence the level of gene expression by enhancing or inhibiting it.
What is transcriptional regulation?
When regulatory transcription factors influence the level of gene expression by inhibiting or enhancing expression.
In both bacteria and eukaryotes, how many ways are there to control protein activity level?
There are 3 ways in which the activity level of a protein is controlled.
What are the 3 ways in which protein activity level is controlled?
1) Transcriptional control
2) Translational control
3) Posttranslational control
What is transcriptional control? Name two examples.
This refers to how much RNA is being made.
The Lac Operon and the Trp operon are examples.
What is translational control? Name an example.
This refers to how heavily the mRNA is being translated.
The use of the antisense RNA to inhibit translation.
What are operons?
In bacteria, there are clusters of genes dedicated to the same biochemical pathway.
T/F: In an operon, the polycistronic mRNA shares regulation for all of these genes in the operon.
True!
What is polycistronic mRNA?
One mRNA that encodes for multiple genes/proteins.
In an operon, where do Shine-Delgarno sequences exist?
They precede the start codons of genes.
What are Shine-Delgarno sequences?
These are located on operons in bacteria and are where the ribosomes will load to translate the mRNA.
Does eukaryotic mRNA have Shine-Delgarno sequences? What are the exceptions?
Eukaryotic mRNA does NOT have Shine-Delgarno sequences EXCEPT in mitochondrial DNA/mRNA and Chloroplast DNA/mRNA.
What is catabolism?
The breakdown of a substance.
What do we mean when we say catabolism is inducible?
We only breakdown a substance for use when we need to. This is for efficiency.
In E. coli and other bacteria, what does the Lac Operon do?
It encodes 3 enzymes that catabolize lactose.
When Lactose is not available to be metabolized, what happens?
The lac operon is shut down by the lac repressor binding to the lac Operator and blocking transcriptional activation.
What encodes the lac repressor protein?
lacI
What does lacI do?
Encodes a repressor protein that binds to the operator.
What type of protein is the lacI protein?
A diffusible protein that binds to the lacO site.
What is the lacO site?
This is the lac operon operator site.
If a repressor protein is bound to lacO, what does this say about the presence of lactose?
There is NOT lactose available to be metabolized.
Generally speaking, when is the Lac operon on?
The Lac operon is only on when Lactose is the most efficient carbon source available.
What is typically the most efficient carbon source? What effect does its presence have on the Lac operon?
Glucose is the most efficient carbon source.
If Glucose is available, the Lac operon will be turned off.
What happens when both lactose and glucose are available?
A small portion of Lactose is spontaneously converted to allolactose, which binds to the lac repressor, inactivating the repressor so it cannot bind to the operator.
Describe the level of transcription when lactose and glucose are available.
There is a basal or low-level of transcription of the lac operon taking place.
Why is there a low-level of lac operon transcription when lactose and glucose are both present?
The glucose is used first. The lac operon is transcribed only slightly because the CAP protein needed for high levels of transcription is inactive when CAP is by itself.
If there is a lack of CAP binding, what does this say about glucose and lactose levels?
Glucose and lactose must both be present.
What happens when there is no glucose but there is lactose?
The absence of glucose causes cyclic AMP (cAMP) to accumulate.
cAMP binds to the CAP protein, which forms a complex that will activate the Lac Operon as long as the Lac repressor is also absent.
What does the cAMP-CAP complex do?
CAP binding enhances the binding of RNA polymerase to the promoter.
What is the binding site for the cAMP-CAP complex called?
The CAP site.
When there is a high rate of transcription, what does this say about glucose and lactose levels?
Glucose is absent and lactose must be present.
What is Anabolism? Is it inducible or repressible?
The biosynthesis of a substance.
It is repressible meaning that the cell will keep making components unless it has enough, then it will be repressed.
What happens when the amino acid tryptophan level is low?
The entire Trp operon is transcribed in order to synthesize tryptophan.
How many enzymes does the trp operon have?
It includes 5 enzymes.
What happens when the amino acid tryptophan levels are high?
The Trp operon will be repressed.
Describe the mechanism for Trp operon repression.
The trpR gene produces a repressor trpR protein. This will bind to tryptophan to form an active complex which binds to the operator to repress it.
What acts as the repressor and co-repressor in tryptophan repression?
The trpR protein is the repressor.
Tryptophan is the co-repressor.
What is a co-repressor?
A small molecule that binds to a repressor, which is usually a protein.
When will tryptophan act as a repressor?
Only when we have sufficient tryptophan that we don’t need to produce anymore.
T/F: The trpR protein is active by itself.
False! It is inactive unless it is bound by its co-repressor, tryptophan.
What is the most common method of genetic regulation in bacteria?
Predominantly at the level of transcription.
T/F: Translational control is more common than transcriptional control.
False! Transcriptional control is more common than translational control.
Describe the action of a translational regulatory protein.
A protein can bind outside the start codon and act as a translational repressor to prevent it from being translated.
T/F: A translational regulatory protein can only bind to one place on the mRNA.
False. The protein can bind on multiple places, such as the 5’ end and start codon, to prevent translation.
What is the Antisense RNA?
It is another RNA that can bind to the mRNA to prevent translation by preventing the ribosome from assembling and binding to the 5’ of the mRNA.
What is an example of using Antisense RNA to inhibit translation?
Regulating the amount of water in a bacterial cell (osmoregulation).
What produces the Antisense RNA?
The micF gene produces the antisense RNA.
What does micF do?
Binds to the ompF RNA to prevent translation and reduce pores that bring water into the cell.
What is an example of posttranslational regulation?
A common mechanism to regulate the activity of allosteric enzymes is feedback inhibition.
What are allosteric enzymes?
Enzymes that can exist in different shapes to be either active or inactive.
What is feedback inhibition?
This is when the final product will go back and inhibit the first enzyme by binding to the regulatory site.
What are the sites in an allosteric enzyme? What enzyme in the feedback loop would this be?
It has a catalytic and regulatory site to be either active or inactive. Enzyme 1 is an allosteric enzyme.
