Chapter 14: Regulation of Cellular Processes

Gene regulation

level of gene expression can vary under different conditions

Constitutive gene

gene that is transcribed at a relatively constant level regardless of the cell environmental conditions

Facultative gene

transcribed only when needed

Three types of gene expression regulatory mechanisms

1. transcriptional

2. translational

3. posttranslational modification

Positive regulation

activator protein promotes transcription

Negative regulation

repressor protein prevents transcription

Adaptive expression

expression of a gene depends on presence of a particular substance

Constitutive expression

gene is expressed continually regardless of environment

Inducible regulation

gene expression is induced by presence of particular substance

Repressible regulation

presence of particular molecule inhibits gene expression

Activators

increase transcription causing positive control and bind to active binding sites

Repressors

inhibit transcription process causing negative control

What to repressors bind to?

operater

Inducers

effector molecules that increase gene transcription by binding to activators

Corepressors

effector molecules that decrease gene expression by binding to repressors

Inhibitors

effectors that bind to activator and prevent activator from binding to DNA

Beta-galactosidase

hydrolyzes lactose into galactose and glucose

If lactose is present how many beta-galactosidase molecules are there?

3,000

If lactose is absent, how many beta-galactosidase molecules are there?

3

Operon

a unit of genetic material that functions in a coordinated manner by a single promoter

Parts of an operon

operator, promoter, structural genes

what does an operon produce

polycistronic mRNA

Leak operons means what

there is a low basal level of transcription

How does different promoter strength affect gene expressoin?

it affects frequency of initiation

lac operon

three structural genes coding for lactose uptake and metabolism

Lac repressor

lacl

What does Lacl do when there is no lactose avaible?

Binds operator and inhibits transcription

LacZ

encodes beta-galactosidase

LacY gene

encodes permease

What does permease do?

facilitates entry of lactose into bacterial cell

LacA gene

encodes transacetylase

Transacetylase

removes toxic by-products from lactose difestion

Structural genes of Lac operon

LacZ, LacY, LacA

Promoter region gene (lac)

lacP

LacP

RNA polymerase binding site

Operator region gene (lac)

LacO

LacO

repressor binding site

Repressor gene (lac)

Lacl

LacL produces

repressor

Lac Repressor

in absence of lactose, each dimer of tetramers bind to 3 operator sites

If lactose is absent the repressor binds to

operator

By the repressor binding to the operator, what happens in gene expression?

DNA is bent, blocking RNA polymerase from accessing promoter

What brings lactose into the cell?

lactose permease

When lactose is pressent, what binds repressor?

allolactose

Lac operon is regulated by

catabolite activator protein

The regulation of lac operon happens in response to

presence or absence of glucose

CAP site

DNA sequence where CAP recognized and binds

CAP facilitates what to bind on promoter

RNA polymerase

CAP binding to CAP site is ____ dependent

cAMP

trp operon

repressible operon the encodes enzymes involved with biosynthesis of tryptophan

The five structural genes of trp operon

TrpE, D, C, B and A

The five structural genes of trp transcribe

polycistronic mRNA

the five structural genes of trp operon produce

tryptophansythetase

Promotoer region gene of trp

P

Operator region gene of trp

O

Negative transcriptional control is by the trp ___

repressor

trp operon only functions in the absence of

tryptophan

when tryptophan is present, the trp operon acts as

corepressor

The ara operon

operon wheihc depends on environmental conditions

when is the Ara operon inactive?

when arabinose is present

when is the Ara operon active?

when arabinose is absent

Transcriptional control of the ara operon is by the

AraC protein

Attenuation

Termination of transcription within the leader region

Transcirption continuation along with transcription initiation is contorlled in what operon

trp

Riboswitches

specialized form of transcription attentuation

Describe riboswitches

folding of RNA leader determines if transcription contrunes

What alters RNA leader seuqence folding pattern?

effector molecule binding to RNA

Ribsowitches in Gram positive bacteria function in

transcriptional termination

T box riboswitch

leader region adopts two configurations for termination or continuation

Effecter molecule binding alters folding of the leader RNA which obstructs what sequence

Shine-Dalgarno

RNA thermometers

RNA secondary structure located in the leader sequences of mRNAs

At low temperature, the gene is

on

At high temperatures, what happens in RNA thermomoeterS?

RNA is denatured and gene is expressed

Antisens RNAs

complementary to mRNA and function by base pairing

What do sRNAs and ncRNAs inhibit

translation

Regulon

genes or operons controlled by a common global regulatory protein

Types of regulation used in global regulatory systems

2-component signal transduction systems, phosphorelay systems, sigma factors, 2nd messengers

Two-component signal transduction

link events outside the cell to gene expression inside the cell

Sensor kinase

spans the PM so a part is exposed to the extracelluar environment while the other part is in the cytoplasm

WHat does sensor kinase do?

phosphorylates itself, then transfers phosphate to response regulaor

What does sensory kinase regulate?

porin

Phosphorelay systems

phosphoryl group is transferred to many proteins through a complex system

What are phosphorelay systems use din

quorom sensing and endospore formation

What are sigma factors needed for?

RNA polyermase to bind a promoter and initiate transcription

Alternate sigma factors

direct RNA polymerase to specific subsets of bacterial promoters

sigma factor 70

genes needed during exponential growth

sigma factor 54

genes involved in N metabolism

sigma factor 38

genes needed during stationary phase and general stress response

sigma factor 32

genes needed to protect against heat shock and other stresses

sigma factor 28

involved in flagellum assembly

sigma factor 24

needed for proper folding of membrane proteins

sigma factor 19

response to iron starvation

Second messengers

small molecules produced in response to a signal from outside the cell

cAMP

brings about coordinate regulation of catabolite operons

what is teh active form of catabolite operons

cAMP bound

when glucose is low how does cAMP production proceed

it’s produced

when glucose is available how does cAMP production proceed?

not produced

Stringent response

global mechanism to slow growth in response to nutirtional stress

Amino acid starvation

slows down growth, metabolic activity and reproduction causing cell to go into survival mode

Alamons

molecules that respond to nutrional stress