Genetics Lecture 27: Gene Regulation in Bacteria

what means that the level of gene expression can vary under different conditions?

gene regulation

genes that are unregulated are termed what?

constitutive (always on)

gene regulation is important for what three cellular processes?

1) metabolism
2) response to environmental stress
3) cell division

what two ways can regulation control transcription?

1) gene regulatory proteins bind to DNA and allow/prevent transcription
2) attenuation: transcription terminates soon after it has begun due to the formation of a transcriptional terminator

what three ways can regulation control tranlation?

1) translational REPRESSOR proteins can bind to the mRNA and prevent translation
2) riboswitches can produce an mRNA confirmation
3) antisense RNA can bind to mRNA

what two ways can regulation occur posttranslationally?

1) feedback inhibition
2) covalent modifications

transcriptional regulation involves the actions of what two main types of regulatory proteins?

- repressors: bind to DNA and inhibit transcription
- activators: bind to DNA and increase transcription

_____ control refers to transcriptional regulation by repressor proteins

negative

_____ control refers to regulation by active proteins

positive

which molecules link environmental conditions to gene regulation?

effector molecules

effector molecules effect _____ regulation and bind to _____ proteins but not to DNA directly

transcription; regulatory

small effector molecules that increase transcription are termed what?

inducers

- bind activators and cause them to bind to DNA
- bind repressors and prevent them from binding to DNA

genes that are regulated by inducers are termed what?

inducible

small effector molecules that inhibit transcription are termed what

- corepressors: bind to repressors and cause them to bind to DNA
- inhibitors: bind to activators and prevent them from binding to DNA

genes that are regulated by effector molecules that inhibit transcription are termed what?

repressible

both activators and repressors must be _____ to environmental signals

sensitive

regulators have what two sites?

1) a DNA binding site
2) an allosteric site that binds the small effector molecule

DNA binding site and allosteric site is _____

coupled

what is it called when a particular enzyme appears in the cell only after the cell has been exposed to the enzymes substrate?

enzyme adaptation

an operon is a _____ unit consisting of a few structural genes under the control of _____ promoter and associated regulatory sequences

regulatory; one

an operon typically encodes a _____ mRNA that contains the coding sequence for two or more structural genes

polycistronic

what are the 3 DNA elements on the lac operon? what are their functions?

- promoter: binds RNA polymerase
- operator: binds the lac repressor protein
- CAP site: binds the activator protein Catabolite Activator Protein

what are the structural genes on the lac operon?

lac Z, lac Y, lac A

what is the function of lac Z?

- encodes B galactosidase
- breaks down lactose to galactose and glucose
- also converts lactose to allolactose

what is the function of lac Y?

- encodes lactose permease
- membrane protein required for transport of lactose and analogs

what is the function of lac A?

- encodes B galactoside tranacetylase
- covalently modifies lactose and analogs
- prevents toxic buildup of nonmetabolizable lactose analogs

t/f lacI gene is part of the lac operon

false
- it has its own promoter (i promoter)

the lacI gene is _____ expressed at low levels

it encodes the _____, lac protein

the lac repressor protein functions as a _____

constitutively; lac repressor; tetramer

t/f the binding of the polymerase to the promoter and the repressor to the operator can happen at the same time

false

the lac I repressor can only bind if what?

there is no inducer present

the lac operon can be transcriptionally regulated in what 2 ways?

1) By a repressor protein- responds to the presence/absence of lactose (involves a lac repressor protein; inducer is allolactose- binds to lac repressor and inactivates it)

2) By an activator protein- responds to the presence/absence of glucose

if there is lactose in the environment, then some of it gets converted to what?

allolactose

when allolactose is available, it binds to the _____; this prevents it from binding to the operator site, thus allowing transcription

repressor

the lac operon is induced only in the presence of _____

lactose

what is the synthetic inducer that does not induce lac enzymes and is not hydrolyzed?

IPTG

with _____, induction can be separated from lactose metabolism

IPTG

lac + is _____ while lac - is _____

dominant; recessive

what are the two classes of constitutive mutants that are always on

Oc, lac I-

what does it mean if the operator is cis-acting?

it control gene immediately adjacent to it (downstream)

WT lacY in cis to O=, lacY ON only in presence of _____

lactose