Topic 10: Regulation of Gene Expression

Alter

________ the activity of enzymes and other proteins (called post-= translational control) because it occurs after the proteins are produced.

Glucose

________ is preferred sugar source, but lac operon can produce β- galactosidase (able to catabolize lactose- split into galactose and ________)

CAP activity

________ is modulated by cAMP.

tryptophan

In the absence of ________, the repressor dissociates from the operator, and the RNA synthesis proceeds producing ________.

Trp operon

________ is an example of "negative "control.

DNA

histone like protein

DNA polymerase

IV and V; sos reponse

mRNA

smaller, unstable, degrade quickly

mRNA

polygenic (encode for more than 1 gene, some Archaea), no splcing

Expressed the gene(s) = transformation (at least 23 genes required)

does not happen easily to eukaryotes, frequent in bacteria

constitutive genes

housekeeping genes that are expressed continuously

facultative genes

expressed as need

inducible genes

genes that code for inducible enzymes such as β-Galactosidase

example

E. coli that was on meat is now on cutting board

example

formed biofilm at bathroom sink, then cleaned with cleaning solution

example

salmonella on fruits, lunch meat, ice cream

lab

fermentation tube

(i.e glucose to lactose

b/c of operons

glucose is preferred sugar source, but lac operon can produce β-galactosidase (able to catabolize lactose

split into galactose and glucose)

adenyl cyclase

active only when little or no glucose is present

I = repressor (constitutive gene = "housekeeping" gene) → always on

blocks RNA polymerase

2 mechanisms of control (positive and negative)

repressor and CAP

High glucose & lactose available → nothing present → very low (basal) level of gene expression (high glucose therefore no CAP, lactose unlocks repressor protein, causes inefficent expression

not working properly)

new slide

the regulator protein has a defective operator-binding site

new slide

super repressor (lactose-binding site altered; no binding to lactose → repressor always bound to operator, blocking transcripition.)

has two mechanisms

Tryptophan/trp repressor and attenuation

this type of regulation, called attenuation, was first demonstrated with trp operon (2nd mechanism

how to stop)

Riboswitches

a regulatory segment of a mRNA that binds a small molecules, resulting in a change in protein production

Modulon

multiple regulon individually controlled (lac operon) but also controlled globally

Lac operon

promotor

The experiment by Fred Griffith in 1928 involving injecting bacteria in mice showed ___

transformation; some strains are pathogenic (ones with capsules) and some are not; the non-pathogenic strain took up DNA fragments from pathogenic strain and thus "transformed"

What changes the rate of protein synthsis because it controls the transcription and translation of genes in the formation of proteins?

regulation of gene expression

What alters the activity of enzymes and other proteins that occurs after the proteins are produced?

post translational control

What are the levels of regulation of gene expression?

transcription initiation, transcripition elongation, translation, and post translation

True or False: the three domains of life differ in genome structure and regulatory mechanisms used.

true

What is regulation of trancription initiation

induction and repression of enzyme synthesis

What are consitutive genes?

"housekeeping" genes that are expressed continously

What are facultative genes"

genes that are expressed as need

What are inducible genes?

genes that code for inducible enzymes such as beta-galactosidase

Regulatory proteins either ___ or ___ transcription.

inhibit (negative control) or promote (positive control)

Regulatory proteins are modulated by ___

inducers, corepressors, and inhibitors

Why do bacteria need to adjust/adapt gene expression/regulation?

environment changes constantly; need to adapt quickly for survival therefore no waste of resources

What is diauxic growth?

a biphsic growth pattern in which there is preferential use of one carbon source over another when both are available in environment

What occurs after preferred substrate is exhausted followed by the resumption of growth using the second source?

lag

What helps bacteria switch nutrition quickly?

operons

What are operons?

seqences of bases coding for one or more polypeptides along the promoter and operator or activator binding sites

What is an example of positive transcripitonal control of inducible genes?

lac operon

What is an example of negative control?

trp operon

What is the preferred sugar source?

glucose

What does beta-galactosidase do to lactose when glucose isn't present?

split lactose into galactoe and glucose

Presence of regulatory protein at regulatory site ___ mRNA synthesis

decreases

Absence of a regulatory protein at regulatory site ___ transcription

promotes

What regulates the lac operon?

catabolite activatory protein (CAP) and cyclic AMP (cAMP)

CAp activity is modulated by ___

cAMP

Levels of cAMP is controlled by ___ which converts ATP to cAMP and PPi

adenyl cyclase

Adenyl cyclase is active only when ___

little or no glucose is present

In an absence of glucose, CAP is ___ and promotes transcription.

active

The three sequences on the lac operon is ___

repressor, beta-galactosidase, and permease

What are the two mechanism of control in the lac operon?

repressor and CAP

The lac operon is a ___

negative inducible gene

When there is low glucose and lactose available ...

lac genes strongly expressed bc presence of CAP

When there is a high glucose and lactose unavailable ...

lac genes not expressed bc repressor stays attached and no CAP

When there is low glucose and lactose unavailable ...

lac genes not expressed bc repressor stays attached and CAP attaches

When there is high glucose and lactose available ...

very low level of gene expression bc no CAP and repressor protein not attached

CAP is associated with ___ levels

glucose (high glucose = no CAP)

Repressor protein assocated with availabity of ___

lactose (when available, repressor isn't attached)

the tryptohpan operon is a ___ system

negative repressible system

The trp operon consists of 5 ___ which code for enzymes needed to synthesize tryptohan

structural genes

The trp operon functions only in ___ of tryptophan.

absence

What are the two mechanism of trp operon?

repressor and attenuation

When trytophan is present ...

the trp repressor binds to the operator and RNA synthesis is blocked therefore there is no production of tryptophan

In absence of trytophan ...

repressor dissociates from the operator and RNA synthesis proceeds producing tryptophan

What is attenuation?

regulation of transcription termination

When attenuation occurs later on the gene ...

tryptophan is not produced

When attenuation occurs eariler on the gene ...

tryptophan produced but slow

What are riboswitches?

regulatory segment of mRNA that binds a small molecule resulting in a change in protein production

Folding of leader sequence (the riboswitch) determines ___.

if transcription will continue or be terminated

Low concentration -> riboswitch ___ and translation ___.

attached; occurs

High concentration -> riboswitch ___ and translation ___.

substrate is attached to riboswitch; blocked

Why are global regulatory systems important for bacteria?

bacteria must respond rapidly to a wide variety of changing environmental conditions

What are two global regulatory systems?

regulon and modulon

What is regulon?

global regulatory system; genes or operons controlled by a common regulatory protein

What is modulon?

global regulatory system; multple regulon individually controlled but also globally controlled

Most archaea regulatory proteins function like bacteria ___ and ___ because they bind DNA sites near the promoter or enhance/block the binding of RNA polymerase.

activators and repressors

Some archaea regulatory proteins function like ___ regulatory transcription factors by interacting with a general transcription factor.

eukarya

Feedback inhibition is also called ___.

end product inhibition

What is feedback inhibition?

inhibition of one or more critical enzymes in a pathway regulates entire pathway

What is a pacemaker enzyme?

example of feedback inhibition; catalyzes the slowest or rate limiting reaction in the pathway

How can genes be inserted?

use lac operon's promoter to replace genes with genes of your desire