Chapter 7 - "Microbial Regulatory Systems"

What is a diauxic growth curve?

A consequence of catabolite repression that leads to two exponential growth phases. If two usable energy sources are available, the cells first consume the better energy source.

What is feedback inhibition?

A process in which an excess of the end product of a multistep pathway inhibits activity of the first enzyme in the pathway.

How does the response of the chemotaxis system to an attractant differ from its response to a repellant?

An increase in attractant decreases the rate of CheA autophosphorylation and the response regulator CheY remains unphosphorylated. An increase in repellant concentrations increases the rate of CheA autophosphorylation.

Compare and contrast the activities of an activator protein and a repressor protein

Binding of an activator protein to DNA results in stimulating transcription. Binding of a repressor protein to DNA results in blocking transcription.

What are some examples of a stringent response in bacteria? -Example of stringent response: C. crescentus

C. crescentus naturally inhabits freshwater systems that are limited in nutrients. If cells encounter severe nutrient limitation, the stringent response is induced as ppGpp production increases, leading to cell morphology changing from stalked cells to swarmer cells that can swim to find more nutrients.

How are constitutive proteins different from inducible proteins?

Constitutive proteins are needed at the same level under all growth conditions in the cell. Inducible proteins are synthesized only when they are needed.

What is an isoenzyme?

Different enzymes that catalyze the same reaction but are subject to different regulatory controls.

What is the role of phosphatases in two-component regulatory systems?

For a balanced regulatory system to work properly, it must have a feedback loop to complete the regulatory circuit and terminate the response, resetting the system for another cycle. This feedback loop employs a phosphatase. Phosphatase activity eventually returns the response regulator to the fully non phosphorylated state if kinase activity is reduced.

What role does cyclic AMP play in glucose regulation?

Glucose inhibits synthesis of cAMP and transports it out of the cell. When glucose enters the cell, cAMP level is lowered, CRP can't bind to DNA, and RNA polymerase fails to bind to the promoters of operons subject to catabolite repression. The direct cause of catabolite repression is a low level of cAMP, which is caused by the presence of glucose.

What is an inducer?

If the binding of an effector to a transcription factor results in turning transcription on, the molecule is considered an inducer.

What is the role of kinases in two component regulatory systems?

In two-component regulatory systems, kinases (sensor kinase) phosphorylate themselves in response to an external signal and then transfers the phosphoryl group to a response regulator protein (the other protein that makes up this two-component system)

How does attenuation work?

It is a transcriptional control that functions by premature termination of mRNA synthesis. control is exerted after initiation f transcription but before its completion. The mRNA step loop structure and the synthesis of the leader peptide are determining factors of attenuation.

What are kinases?

Kinases are enzymes that phosphorylate compounds usually using phosphate from ATP.

What advantage do quorum-sensing systems confer on bacterial cells?

Many bacteria use this approach to ensure that sufficient cell numbers of their own species are present before initiating activities that require a certain cell density to work effectively.

How do bacteria control what proteins are being expressed?

Microbes regulate protein function in two distinct ways. One mechanism controls the amount of an enzyme or other protein, whereas the second controls the activity of a preform enzyme or other protein.

What would happen to regulation from a promoter under negative control if the region where the regulatory protein binds was deleted? What if the promoter was under positive control?

Negative: Transcription will proceed unstopped because nothing will inhibit RNA polymerase from transcribing the genes in that operon. Positive: Transcription will not occur because RNA polymerase needs the binding protein (activator) to attach to the promoter region of that operon.

Distinguish between an operon and a regulon.

Operon: two or more genes transcribed into a single RNA and under the control of a single regulatory site Regulon: a series of operons controlled as a unit

What are phosphatases?

Phosphatase is an enzyme that removes the phosphate from the response regular protein at a constant rate

How is positive control different from negative control?

Positive control activates transcription and negative represses/stops transcription.

What are heat shock proteins?

Proteins induced by high temperatures that protect against high temp, especially by refolding partially denatured proteins or by degrading them

Why would cells want to control what protein is expressed?

Some may be needed and others may not be needed.

What is the difference between an allosteric site and an active site?

Substrates bind to an active site, whereas end products of a pathway bind to an allosteric site. When an end product is in excess, it binds to an allosteric site, changing the conformation of the enzymes to where the substrate can't bind at the active site.

Explain how catabolite repression depends on an activator protein.

The activator protein is called cyclic AMP receptor protein (CRP). A gene that encodes catabolite repression enzyme is expressed only if CRP binds to DNA in the promoter region.

What causes bacteria to fluoresce? What gene codes for this enzyme?

The enzyme luciferase causes bacteria to fluoresce and the genes that encode for it are in lux operons.

***How does the lac operon work?

The lac operon is only transcribed when glucose is absent and other sugar sources are needed. It is physically blocked by a repressor protein when lactose is not needed. When an inducer protein binds, it changes its shape and falls off of the operator and transcription of the lac operon can proceed. The repressor's role is inhibitory so the operon is under negative control.

What do repressor proteins bind to?

The repressor protein binds to the operator region to block or repress transcription.

What is catabolic repression?

The suppression of alternative catabolic pathways by a preferred source of carbon and energy.

Why does attenuation control not occur in eukaryotes?

Unlike prokaryotic cells, the processes of transcription and translation are spatially separated in eukaryotes.

What are some examples of a stringent response in bacteria? -Example of stringent response: E. coli

When cells of E. coli are voided in the feces and face a switch from the nutrient-rich intestine to an open water system, the reduction in nutrients triggers ppGpp synthesis to initiate the stringent response. As ppGpp production increases, cell division is inhibited.

What is the inducer for the lac operon?

allolactose

***Explain how the lac operon is both positively and negatively controlled.

positive - for lac to be transcribes the level of cyclic amp must be high enough for CRP to bind to CRP binding site negative- lactose or another inducer must be present so the lactose repressor doesnt block trancription by n=binding to operator