Gene regulation/expression

types of gene regulation

allosteric regulation and covalent modification

Allosteric regulation

regulatory enzyme is controlled by an effector binding reversibly to enzyme at the regulatory site, changing shape and activity

Covalent modification

addition/removal of particular chemical group switches enzyme on or off

Regulation of mRNA synthesis

use sigma factors

Types of enzymes

constitutive, inducible, repressible

Constitutive enzyme

expressed all the time

Inducible enzyme

amount is increased by presence of an inducer, catabolic pathways

Repressible enzyme

amount is decreased by presence of a repressor, anabolic pathway

Negative control

mRNA synthesis stops in presence of repressor

Positive control

mRNA synthesis turned on in presence of activators

Negative control of inducible gene

repressor bound (no transcription) or inducer binds to repressor - repressor not bound (transcription occurs)

Negative control of repressible gene

repressor not bound (transcription occurs) or corepressor binds to repressor - repressor bound (no transcription)

Positive control of inducible gene

activator not bound (no transcription) or inducer binds to activator - activator bound (transcription occurs)

Positive control of repressible gene

activator bound (transcription occurs) or inhibitor binds to activator - activator not bound (no transcription)

Operon

sequence of base coding for 1+ polypeptide with a promoter and operator or active binding site

Lac-operon

b-galactosidase, lactose permease, negative regulation

If lactose isn’t available in lac-operon

lac repressor is active and binds to operator, inhibits transcription

If lactose is available in lac-operon

b-galactosidase cleaves lactose into allolactose (inducer), allolactose binds to repressor, inactivates it, repressor can’t bind, transcription occurs

Lactose permease

allows lactose to come into cell

B-galactosidase

breaks lactose down into glucose and galactose for metabolic pathways

Catabolite activator protein (CAP)

binds DNA in presence or absence of cyclic AMP, is cAMP bound to CAP, transcription occurs

Glucose, no lactose

CAP inactive/not bound, repressor bound, inhibit transcription

No glucose, no lactose

CAP active/bound, repressor bound, transcription blocked

Lactose, glucose

CAP inactive/not bound, repressor inactive, inhibit transcription

Lactose, no glucose

cAMP binds to CAP, CAP active/bound, repressor inactive, transcription occurs

Glucose available

CAP inactive/not bound, no transcription

Glucose not available

increase in cAMP to bind to CAP

Lactose available (CAP)

repressor inactive/not bound

Lactose not available (CAP)

repressor active/bound, no transcription

Low trp levels

trp repressor inactive/not bound, transcription occurs

High trp levels

trp repressor active/bound, no transcription

Global regulation

control many gene and pathway simultaneously, outer membrane and sensor kinase

Ways to regulate genes and pathways

outer membrane protein and sensor kinases

Outer membrane protein

gram -, bring molecules into cell

Sensor kinase

activated when it senses molecules are present by osmotic pressure, makes protein bigger or smaller

Gene regulation of translation

antisense RNA and riboswitches

Antisense RNA

small RNA molecules (antisense RNA) bind to mRNA to prevent translation

Riboswitch

regulation occurs in folding of mRNA by effector molecules