Lecture 14- Microbial gene regulation II

lac operon

is an operon of genes involved in the degradation and metabolism of sugar lactose

glucose and galactose

Lactose is a disaccharide composed of two sugars ________ and _________.

source of energy

By degrading lactose into these sugars, the. cell can obtain a__________. This is the logic and function behind the lac operon.

lactose is present

Problem 1: Expression should only take place when __________. Otherwise, we are wasting cellular resources in a futile effort

absence of glucose

Problem 2: we should only express the lac operon in the ____________. otherwise it is unnecessary.

Diauxic growth

Cellular growth characterized by two distinct phases

glucose

What is the preferred sugar energy source?

represses

the presence of glucose ______ the synthesis of the lac operon proteins. However when glucose is depleted, the cell can switch to using lactose, albeit at a slower rate.

lactose metabolism

the proteins encoded in the lac operon are used in ____________

LacZ (B-galatosidase)

degrades lactose

LacY (lactose permease)

transports lactose

LacZ (transacetylase)

Unclear (Toxicity)

unbound activator or a bound repressor

We have a system that would like to be OFF under normal conditions. therefore we are going to be dealing with an __________ or a ___________.

Lacl

The repressor protein of the lac operon, blocks RNA polymerase from binding to the promoter

lac repressor (Lacl)

In the absence of lactose the _____________ binds to the lac operator as a dimer.

Represses, negative

Binding of the Lacl _________ gene express, what type of system is this?

lactose

The cofactor in this system is ?

binds to Lacl

When lactose is present in the it _________. This binding results in a conformational change in Lacl.

allows RNA polymerase to bind, inducible system

becomes unable to retain its dimeric state and releases DNA. What does this allow and what type of system is this?

lac represser Lacl

In the absence of lactose, the _____________ binds the lac operator as a dimer.

represses, negative system

Binding of Lacl _______ the system. What type of system is this?

lactose

The co-factor in this system is __________ (allolactose).

binds to Lacl

When lactose is present in the cell it ________. This binding results in a conformational change in LacI

Lacl-lactose

____________ becomes unable to retain its dimeric state and releases the DNA.

allows RNA polymerase to bind, inducible system

Lacl-lactose being unable to retain its dimeric state allows __________ and turns on gene expression. What type of system is this?

absence, OFF

Lacl in the _______ if lactose, dimerizes and binds lacO blocking RNAP binding. Is the gene off or on?

inducer, ON

In the presence of lactose. Lactose acts as an _________, binding an allosteric site on Lacl. Gene is off or on?

Lacl dimer, upstream Lacl binding site

The _______ doesnt just bind the promotor region of DNA it also binds an __________.

homotetratmer, loop

These two dimers can bind one another to form a ___________ causing DNA to form a _________.

the repression, RNA polymerase, bind to lacP.

This loop improves ____________ by Lacl, as ____________ becomes less able to __________.

not required

In the presence of glucose and lactose the lac operon is __________.

depleted

Only when glucose levels are ______ its high expression of the lac operon is required.

sigma-factor RpoD, recognition sequences

Responding to glucose involves the ________ and its ________ in the lac operon.

consensus sequence

Remember that, RpoS has a __________ at the -35 and -10 regions.

lac operon's sequences, differ

The _____________ at these regions (-35 and -10 regions) _________ greatly.

without an activator

Because they differ greatly that means ________ expression from this promoter sequence is very low.

does not detect

The lac operon ____________ glucose levels directly

secondary messenger molecule (cylic-AMP)

Instead the presence of glucose is detected indirectly though a ______________

Secondary messenger

a molecule that relays a cellular signal. Think of it as a middle man.

Clyclic-AMP

A cyclic version of adenine-monophosphate. it is made in the absence of glucose from ATP.

high

cAMP levels are _______ when glucose is low.

improved expression

The cyclic-AMP produced can result in _______ of the lac operon by binding to the activator, cAMP receptor protein (CRP).

cAMP receptor protein (CRP), positive

An activator protein which recruits RNA polymerase to the lac promoter. This is a __________ system.

CRP is unable to dimerize

In the absence of cAMP (high glucose), _____________. Therefore, t does not activate gene expression.

cAMP, binds CRP

When the co-factor, _____, is present it ________ resulting in a conformational change.

able to dimerize, activating

When cAMP binds CRP it results in a conformational change, CRP is now _________ and bind to RNA. It recruits RNA polymerase, ____ gene expression.

inducible

The co-factor cAMP activates gene expression, this means it is an ___________ system.

cAMP is made

Under low glucose conditions the secondary messenger _________.

positive inducible activator

Cyclic-AMP binds the cyclic-AMP receptor protein (CRP) which acts as a _______________.

increases

CRP-cAMP binds as a dimer aiding RNAP binding. This dramatically ______ expression.

absence of lactose, OFF

In the ___________, the pathway is turned off by Lacl repression. Expression of the lac operon is _______.

presence of lactose, low

In the ____________, allolactose will bind to Lacl resulting in a conformational change. Lacl can no longer bind DNA and repression is relieved. Expression of the lac operon is _______.

presence of glucose, LOW

In the _________ there is very little cyclic-AMP (cAMP). Therefore, cAMP does not bind to the CRP activator. Expression of the lac operon remains ______.

absence of glucose, high

In the ___________ more cAMP is produced. The cAMp binds CRP, causing it dimerize and bind DNA. Expression of the lac operon becomes _______.

Operon

series of genes under the control of a single promoter. Often these genes serve a similar function.

Regulon

Multiple operons under the control of a single regulatory protein

spread out, MalT, one

In E. coli the genes requires for maltose utilization are ______ across the chromosome and not in a single operon. This means ____, the maltose activator protein, controls expression of more than ____ operon.

Archaea

Operons and regulons are also present in _________