MBB lec 22 prok transcription LAC OPERON

whats the operon model

-OPERON = regulatory region + structural genes

-controlled by OPERATOR (dna site)

Operon consists of regulatory region and structural genes, what are those 2?

REGULATORY REGION:

-activator binding site (activator binds to enhance transcription)

-promoter (rna poly binds)

-operator (repressor binds to block transcription)

STRUCTURAL GENES (A,B,C)

-transcribed tgt as ONE mRNA (polycistronic)

-encode proteins with related functions

how do regulatory proteins control transcription? by affecting what

by affecting RNA polymerase access (positive vs negative regulation)

explain negative vs positive regulation

Negative regulation

-when off: repressor bind to operator = block rna poly = no transcription

-when on: inducer (effector molec) bind to repressor = change its shape, repressor release dna, rna poly can transcribe

Positive regulation

-activator binds upstream site = HELP rna poly bind = increase transcription

gene expression is controlled by:

environmental signals (effectors)

-allow bacteria to turn genes on/off as needed

do bacteria like e.coli prefer glucose or lactose as carbon/energy source? why not the other

-prefer glucose (can be used directly in glycolysis to produce ATP+pyruvate)

-can use lactose, but must be broken down first (hydrolyze it to glucose and galactose (via enzyme B-galactosidase, which produced at low levels))

what is the isomer of lactose thats the inducer of lac operon

Allolactose

in lac operon, what is the promoter, operator, activator binding site, and structural genes

Promoter: RNA polymerase binding site

Operator: a negative site bound by lac repressor protein

-operator overlaps with promotor, and when lac repressor bound, rna poly CANT bind to promotor to start transcription

CAP (activator) binding site: a positive site bound by catabolite activator protein (CAP)

-when glucose low, CAP triggers cAMP production and will bind to cap (cAMP/CAP) = help rna poly bind/promote transcription

Structural genes: Lac Z (produce B-galactosidase), Lac Y (Permease), Lac A (Transacetylase)

-these encode proteins that import/metabolize lactose

what happens when glucose is present/high?

low cAMP production = CAP dont bind to CAP activator site

what happens when lactose absent vs present

lactose absent: repressor bind to operator = NO transcription

Lactose present: allolactose bind to repressor (change its structure)

-repressor dissociates from operator = transcription

why does transcription need low glucose and present lactose

low glucose: higher cAMP = allows for activator binding

lactose: inducer (hero) binds to repressor

for each situation, explain transcription or not and at what level. when glucose/lactose present or not, and if CAP binds and if repressor on

functions of each enzyme (and what structural gene they made by) produced from lac operon

LacZ → B-galactosidase

-BREAK LACTOSE into glucose/galactose

-convert some lactose into inducer allolactose

-play role in metabolism/regulation

Lac Y → Lactose Permease

-membrane transport protein (import lactose into cell, available for metabolism)

LacA → Transacetylase

-helps cell neutralize and REMOVE TOXIC lactose-like molecs

in summary, Y brings lactose into cell, Z breaks it down, and A removes toxic lactose-like molecs