Lesson 8 Gene Regulation in Bacteria Flashcards
What is transcriptional regulation?
Gene regulation that occurs during transcription.
What kind of gene regulation is most common in bacteria?
Transcriptional regulation
What are the two types of regulatory proteins?
Repressors and activators
Repressor protein
Regulatory protein that binds to the DNA to inhibit transcription
Activator protein
Proteins that increase the rate of transcription
Negative control
Transcriptional regulation by repressor proteins
Positive control
Transcriptional regulation by activator proteins
How does an effector molecule exert its effects?
It binds to a regulatory protein such as an activator or a repressor.
Inducer
Small molecule that will cause transcription to increase
Corepressor
Small molecule that binds to a repressor protein and causes protein to bind to the DNA
Inhibitor
A molecule that binds to an activator protein and prevents it from binding to the DNA
operon
Area in which two or more structural genes are under the transcriptional control of a single promoter
Is it common for bacteria to have genes in operons?
yes
What surrounds an operon?
A promoter to signal beginning of transcription and a terminator to signal the end of transcription.
What regulates the promoter of an operon?
An operator site
What does the lac operon do?
encodes proteins that are involved in lactose metabolism
What is structure of lac operon?
It is made up of two units. The first is known as the lac Oberon and it contains a promoter and three structural genes, lacZ, lacY, lacA. Second unit, with its own promoter, is the lacI gene.
What protein regulates the lac Oberon? H
ow?
Lac repressor protein. It binds to the operator site and prevents RNA polymerase from sliding past the operator site and transcribing the lacZ, Y and A genes.
What dictates the ability of lac repressor to bind to operator site?
It depends on whether or not allolactose is bound to it. When allolactose binds to the repression, it causes a conformational change that prevents the lac repression from binding to the operator site. Under these conditions, RNA polymerase will transcribe the Oberon.
What is induced?
Transcription is startedf
What is repressed?
Repression is bound to the operator site, so there is no transcription.
Experiment 14A: lacI gene
Hypothesis
If the lacI gene encodes a repressor protein, then the lacI gene itself does not have to be physically next to the lac Oberon to repress it; the protein can diffuse throughout the cell and bind to an operator site regardless of the physical location of the lacI gene.
Experiment 14A: lacI gene
How were the data interpreted?
Yellow production in original mutant strain was same with or without lactose. This was expected because beta-galactosidase there was constitutive.
In merozygote, an absence of lactose repressed lac operons. With lactose, both operons (the one on chromosome and the one on the Fâ factor) were induced, yielding a higher level of beta-galactosidase activity in the merozygote.
Trans-effect
Form of genetic regulation that can occur even though two DNA segments are not physically adjacent.
cis-effect or CIS-acting element
DNA segment that must be adjacent to the gene(s) it regulates
Experiment 14A: lacI gene
What was difference between mutant and merozygote strains?
Mutant strain was lacI-, lacZ+, lacY+, lacA+
Merozygote was lacI+ and above
Why does intracellular concentration of cAMP decrease when a bacterium is exposed to glucose?
The presence of glucose inhibits adenylate cyclase, which is necessary for cAMP synthesis. This decreases rate of transcription. This enables bacteria to use two sugars in a more efficient way. First, they will use glucose, then lactose.
How many operator sites does lac operon have?
Three. O1, O2, and O3
How do the operator sites of the lac operon work?
The lac repressor must bind to two out of three operators to cause maximal repression. O1 to O2, or O1 to O3, but not O2 to O3.
What regulates the trp operon?
A repression protein and attenuation.
What does trp operons do?
It encodes enzymes that are necessary for the biosynthesis of the amino acid tryptophan.
What is attenuation?
A segment of DNA, termed the attenuator, is necessary for this form of regulation. This mechanism has two features. First, there are two tryptophan codon within the sequence that encode the trp leader peptide. Second, the RNA that is transcribed from this region is able to form stem-loop structures. Different combinations of stem=loop structures are possible.
What can the 3/4 loop do?
terminate transcription
On what do conditions that favor the formation of the 3/4 loop for trp operon rely on?
Translation of the trpL gene
What is the purpose of the 3/4 loop?
It is a transcriptional terminator. It causes RNA polymerase to pause the U-rich sequence dissociate from the DNA.
How does 3/4 loop form when there is transcription but no translation?
Region 1 hydrogen bonds to region 2, leaving region 3 to bind to region 4.
How does 3/4 loop form when there are high tryptophan levels?
There is sufficient tryptophan in the cell so translation of trpL gene progresses to its stop codon, where the ribosome pauses. The pausing at the stop codon prevents region 2 from h bonding with any region and therefore allows region 3 to h bond to region 4.
catabolism
Breakdown of a substance
Translational regulation
Regulation of the translation of mRNA
Antisense RNA
complementary to an mRNA. It is used to regulate translation. When antisense RNA binds to the mRNA, it prevents translation.
What are two common ways to regulate protein function?
Feedback inhibition and altering protein function by covalent modification of their structure
Feedback inhibition
Final product in a metabolic pathway often can inhibit an enzyme that acts early in the pathway
What kind of modifications are involved with the assembly of a functional protein?
proteolytic processing, disulfide bond formation, attachment of prosthetic groupswm, sugars or lipids. Typically, these changes are irreversible.
What kind of protein product modifications are reversible?
Phosphorylation (-PO4), acetylation, (-COCH3), and methylation (-CH3)
