Ch.15 Regulation of Gene Expression in Bacteria

Bacteria respond _ to changes in their environment

metabolically

Bacteria regulate _ to synthesize products needed for a variety of normal cellular activity

gene expression

Bacteria adapt to the environment by producing _ only when specific substrates are present

inducible enzymes

For constitutive enzymes, enzymes are _ regardless of the chemical makeup of the environment

continuously produced

In a repressible system, the presence of a specific molecule _ gene expression

inhibits

A repressible system involves molecules that are end products of _

anabolic synthesis pathways

In repressible systems, an abundance of _ in the environment represses gene expression

end product

Example of a repressible system

tryptophan production in bacteria

In a positive control, transcription occurs only when regulator molecule directly stimulates _

RNA production

In a negative control, genetic expression occurs unless shut off by _

regulator molecule

Genes coding for enzymes with similar functions organized in clusters with their regulatory sequences are called _

operons

Transcription is under control of an _

operon

A regulatory region on the same strand is called _

cis-acting

Regulatory regions are located _ from gene cluster

upstream

Trans-acting elements binding at _ regulates clusters negatively or positively

cis-acting sites

CIs- and trans-acting sites are regulatory site events that determine if genes are _ into mRNA

transcribed

Binding of a trans-acting element at cis-acting site can regulate the gene cluster negatively by

turning off transcription

Binding of a trans-acting element at cis-acting site can regulate the gene cluster positively by

turning on transcription

Structural genes code the _ structure of an enzyme

primary

The Lac (lactose) operon has 3 structural genes named

lacZ, lacY, and lacA

LacZ gene

encodes B-galoactosidase

B-galactosidase

Enzyme that converts disaccharide lactose to monosaccharides glucose and galactose

LacY gene

encodes amino acid sequence of permease

Permease facilitates _ into bacterial cell

entry of lactose

LacA gene

encodes enzyme transacetylase

Tansacetylase is involved in

the removal of toxic by-products of lactose digestion from the cell

The Lac operon structural genes are transcribed as _

a single unit

The lac operon structural genes result in _

polycistronic mRNA

Cistron

part of a nucleotide sequence coding for a single gene

When the lac operon structural genes are transcribed, a single mRNA is simultaneously translated into _

three gene products

Lactose stimulates the transcription of _ and induces synthesis of enzymes

lac operon

Gratuitous inducers

chemical analogs of lactose

IPTG (isopropylthiogalactoside)

sulfur analog of lactose

Constitutive mutations

Genes with these mutations produce enzymes regardless of lactose presence/absence

Constitutive mutation lacI- gene

Not part of the lac operon structural genes

Produces repressor molecule, which regulates transcription of structural genes

Operator region if operon has a class of constitutive mutations, _, that produces effects identical to _

lacOc; lacI-

In the negative control of the operon model, a group of _ is expressed and regulated as a unit

genes

In the negative control of the operon model, transcription only occurs when the _ fails to bind operator region

repressor

In the negative control of the operon model, the repressor is _

allosteric

In the negative control of the operon model, the repressor

reversibly interacts with another molecule

causes conformational change in shape and chemical activity

In the negative control of the operon model, the repressor normally binds _ in the operator region

DNA sequence

In the negative control of the operon model, the repressor inhibits _ and represses _ of structural genes

RNA polymerase; transcription

The operon model invokes a series of molecular interactions between _

proteins, inducers, and DNA

When there is no lactose in the operon model

Enzymes are not needed, and the expression of genes encoding enzymes is repressed

When lactose is present in the operon model,

the activation of genes is induced by binding repressor

When all lactose is metabolized in the operon model,

none is available to bind to the repressor, and transcription is repressed

3 predictions from the operon model led to its validity

I gene produces diffusible product (trans-acting)

O region is involved in regulation- no product

O region must be adjacent to structural genes to regulate transcription

The creation of _ bacteria allows for the determination of the operon model

partially diploid

Merozygotes

cells diploid for certain added genes

In the absence or presence of lactose partial diploid, _ used to prove operon model for the lac operon

merozygotes

Mutations of the I gene should have _ effects of I-

opposite

Mutant molecules cannot interact with _

inducer

Binding of lactose to _ causes allosteric change in DNA binding domain

inducer-binding domain

The nature of the repressor was not known in _

1961

In 1961, it was assumed that an allosteric repressor was a _

protein

In 1961, RNA was considered a _

repressor

In 1966 Gilber and Muller-Hill reported

the isolation of lac repressor in purified form

The isolation of repressor confirmed the _ model

operon

When the cell has ample amounts of glucose and lactose, _ is not made

B-gakactosidase

_ is the preferred source of carbon for E.coli

Glucose

Catabolite-activating protein (CAP) helps _ the expression of the lac operon

activate

Catabolite-activating protein (CAP) is able to _ expression in the presence

inhibit

Catabolite repression is also called

inhibition

In the absence of glucose and presence of lactose, CAP exerts _ control over lac operon

positive

In the absence of glucose and presence of lactose, promoter region bind to CAP-binding site, facilitating _ binding at promoter and facilitating transcription

RNA polymerase

cAMP

cyclic adenosine monophosphate

To bind to promoter, CAP must be bound to _

cAMP

Glucose inhibits the activity of _, which catalyzes the conversion of ATP to cAMP

adenylyl cyclase

cAMP prevents CAP from binding when _ is present

glucose

A complex is formed when cAMP-CAP and _ are together in the presence of lac promoter DNA

RNA polymerase

Five contiguous genes on E. coli chromosome encode enzymes for _

tryptophan synthesis

When tryptophan (corepressor) is present, _ and _ attain new conformation

repressor; tryptophan complex

When tryptophan (corepressor) is present, the complex binds to the operator, repressing _

transcription- enzymes not made