trigger gene expression

3 steps gene expression can be controlled at

transcription

translation

post translational modification

Stopping before mRNA is made

(stopping during transcription)

if no mRNA then ribosomes cant mek genetic product

transcription control

transcription control

occurs when regulatory proteins affect RNA poly's abilitiy to bind to a promoter and initiate trancription

DNA--/-->mRNA

Translational control

occurs when regulatory moelcules alter the lenght of time an mRNA survives before its degraded by ribonucleases

OR

affect translation initianton

OR

elongation

post translational control

some proteins are manufactured in an active forma and have to be activated by chemical modification

(phosphorylation)

opp=dephosphoylation

Pros for transcriptional control

saves most energy for cells if stop at earliest point

Pros for translational control

allows a cell to make rapid changes in relative amnts of different proteins

pros for post tranlation control

provides most rapid response

constitutively

always occuring

always present

glycolysis

begins w/glucose

main pathway for the production of ATP

(lactose is also used  but ONLY when glucose depleted)

β- glactosidease

catalyzes the rsn that breaks lactose down into glucose and galactose

Glyolytic pathway

glucose that is released in glycolysis goes into this pathway

inducer

substrate in a rxn that stimulateds the expression of a specific gene

(lactose)

how to produce much β- glactosidease

lactose very high

(No glucose is present)

genes that cant use lactose lack..

lackeither

β- glactosidease

OR

lactose transporter protein

mutagens

chemicals that damage DNA and INC mutation rate

medium

a liquid or solid that supports growth

replica plate

cells from the velvet stick to the plates surface, producing an exact copy of the lcoation of the colonies on the master plate

Indicator plates

where mutants with metabolic deficiences are observed directly

Cells that cannot cleave indictor molecule even if galactose is present as an induceer

means?

no β- glactosidease

gene for β- glactosidease is defective

(lacZ defective)

cells the cannot accumulate lactose must mean?

no membrane protein (glactoside permease) to import lactose

- gene for galactoside permease is defective (lac Y)

cells cleave indicator molecules even if lactose is absent as an inducer means?

consitutitve expression of lacZ and lacY 

gene for regulatory protein that shuts down lacZ and lac Y is defective(lacI)

Lac Z

gene for β- glactosidease

lacY

gene for galactoside permease

lacI

gene for regulatory protein that shuts down lacZ and lacY when lactose is absent

negative control

occurs when a regulatory protein binds to DNA and shuts down transcription

positive control

occurs wehn a reg protein binds to DNA and triggers transcription

represson

inhibitor that exerts neg control

(lac I produces on that exerts neg control on lacZ and lacY)

Repressor present, lactose absent....

repressor binds to DNA

transcription is blocked

(lac I synthesized repressor)

Repressor Present, lactos present...

lactose (inducer) binds to repressor

repressor released from DNA

transcription occurs

No repressor , lactose present...

transcription occurs

Operon

a set of coordinately regulated bacterial genes that are transcribed together into one mRNA

lac A

found to be tightly linked with laxZ and lac Y

-codes for enzyme transacetylase

transacetylase

-protective

-catalyzes certain types of sugars to be exported when they are too abundance

-coded by lacA

allosteric regulation

-small molecule binds directly to a protein and causes it to change its shape and activity

(inducer-lactose-binds to repressor neg control ends; transcripiton can proceed)

importance about lac operon model

gene expression is regulated by physical contact btwn regulatory proteins and specific regulatory sites in DNA

catobolite repression

 positive transcriptional control

end product of a catabolic pathway inhibits further transcription of the gene encoding an enzyme early in the pathway

(ex-hydrolysis of lactos into subunits by β- glactosidease)

catabolite in the catabolic repression of lac operon

glucose

-when abundant in cell transcriptiono f lac operon is decreased

HIGH glucose ouside the cell

inside.......

inactive adenylyl cyclase

LOW cAMP

CAP does NOT bind to DNA

= infrequent transcritpion

LOW glucose outside the cell

inside cell....

active adenylyl cyclase

HIGH cAMP

CAP-cAMP complex binds to DNA

=frequent transcription

catabolite activator protein

(CAP)

(+) control of lac operon depends on theis regulatory protein

CAP binding site

lcoated just upstream of lac operon

strong promoters...

allow efficient initiation of transcription by RNA polymerase

weak promoters

support much less efficient initiation of transcription

lac promoter is weak 

how is that fixed?

CAP reg protein is bound to CAP site the protein interacts w/RNA poly and allows transcription ot begin much more frequently

cyclic AMP

(cAMP)

CAP cant bind to the CAP binding site unless this reg molecule binds to it

When cAMP present....

-cAMP-CAP complex forms and binds to DNA at the CAP site

-RNA poly binds to promoter EFFICIENTLY

*transcription=frequent

When cAMP is absent....

-CAP does not bind to DNA

-RNA poly binds to promoter inefficiently

*transcription = infrequent

adenylyl cyclase

produced cAMP from ATP

-its activity inhibitied by glucose

HIGH glucose LOW cAMP

Lactose Low (repressor binds to DNA)

Infrequent Transcription

infrequent transcription

LOW glucose HIGH cAMP

HIGH lactose (repressor removed)

frequent transcription