Genetics Unit 3- Lecture 15

low levels

many prokaryotic gene products are present continuously at __________; these can increase as needed

environment

Bacteria respond metabolically to changes in their

____________, and they regulate gene expression to

synthesize products needed for a variety of normal cellular

activity.

DNA replication, recombination, repair, and cell division

Genes in prokaryotes that are affected by environment are ___________, ___________, ________, and __________

always on

constitutive gene expression means what

turned on when inducer in present

Inducible gene expression means what(lac gene expression)

turned off when repressor present

Repressible gene express means what

default off

gene expression regulation under positive control means

default on

gene expression regulation under negative control means

constitutive enzymes

Enzymes continuously produced regardless of the

chemical makeup of the environment are called

______________________

inducers

Bacteria adapt to their environment by producing certain

enzymes (inducible enzymes) only when specific

substrates (________) are present.

increase rapidly

In the presence of lactose, concentrations of the enzymes responsible for lactose metabolism _____________

lactose.

The inducer for genes involved in lactose metabolism is

________

operator and a promoter.

The lac operon has three structural genes, lacZ, lacY, and

lacA, with an upstream regulatory region consisting of an

________ and a __________

operon

set of genes with a shared structure and function

ß-galactosidase

The lacZ gene encodes ______________, an enzyme that converts the disaccharide lactose to the monosaccharides glucose and galactose.

lacZ gene

The _________ encodes ß-galactosidase, an enzyme that converts the disaccharide lactose to the monosaccharides glucose and galactose.

permease

· The lacY gene codes for _______________, an enzyme that

facilitates the entry of lactose into the bacterial cell.

Lac Y

· The ____ gene codes for permease, an enzyme that

facilitates the entry of lactose into the bacterial cell.

transacetylase

· The lacA gene codes for the enzyme ____________, which

may be involved in the removal of toxic by-products of

lactose digestion from the cell.

lacA

· The ____ gene codes for the enzyme transacetylase, which

may be involved in the removal of toxic by-products of

lactose digestion from the cell.

single polycistronic mRNA

The structural genes of the lac operon are transcribed as a

______________________

cis-acting.

In bacteria, regulatory regions are almost always located

just upstream of the gene cluster they control and are

______________

Negative control

genetic expression occurs unless it is

shut off by some form of a regulator molecule.

Positive control

transcription occurs only if a regulator

molecule directly stimulates RNA production.

Jacob and Monod (1960)

_______________ proposed the operon model in

which a group of genes is regulated and expressed

together as a unit.

negative control

The lac operon is subject to _______________ because

transcription occurs unless it is shut off by a repressor

molecule.

lac I gene

The _______ regulates transcription of the structural

genes by producing a repressor molecule.

Constitutive mutation I-

lac l gene makes a repressor that has an altered operator-binding region stopping it from binding, causing the transcription of lac genes Z Y A even though there is no lactose present

Constitutive mutation Oc

Nucleotide sequence on operator gene is altered. No binding occurs with repressor and transcription occurs

Super-repression mutation I

Lactose-binding region of repressor is altered so it no longer binds to lactose even if lactose concentrations are high

-repressor always binds to operator no matter what and transcription is inhibited

trans-acting

I gene produces diffusible product (__________)

it can act only in cis

O region does not produce a diffusible product

O region can regulate Z, Y, and A genes only when it is

right next to those genes (_____________)

merozygotes

Partial diploid _____________ can be used to support

predictions of the operon model for the lac operon.

glucose

Even if lactose is present, E.coli's preferred carbon source

is ________. If _______ is also present, it is more

energetically efficient for bacteria to use _________, not

lactose.

CAP

In the absence of glucose and the presence of lactose,

_____ exerts positive control by binding to the CAP-binding

site and facilitating RNA polymerase binding at the

promoter.

positive control

In the absence of glucose and the presence of lactose,

CAP exerts ____________ by binding to the CAP-binding

site and facilitating RNA polymerase binding at the

promoter.

Cyclic adenosine monophosphate (cAMP)

____________________ is required for CAP binding.

adenylyl cyclase

Cyclic adenosine monophosphate (cAMP) is required for

CAP binding. Glucose represses activity of ______________, the enzyme that catalyzes the production of cAMP, and thus prevents

CAP from binding when glucose is present.

Tryptophan

The enzymes for __________ production form an operon

tryptophan

In the presence of ____________, the trp operon is repressed. (If

________ is present, the cell doesn't need to produce more.)

corepressor

Tryptophan functions as a ___________ in the trp operon, which is required for the repressor to bind to the operator.

allosteric transition

Repressor binds to tryptophan causing an _______________ that allows the repressor-tryptophan complex to bind to the operator, blocking transcription

does not restore repressibility

O- (or Oc) mutations on trp operon

· adjacent to structural genes

· no repression ever occurs

· presence of a copy of O+ on a plasmid ___________________

O- (or Oc) mutations

_______________ on trp operon

-transcription is always active

· adjacent to structural genes(cis acting)

· no repression ever occurs

· presence of a copy of O+ on a plasmid does not restore repressibility

restore repressibility

trpR- mutations

· no repression ever occurs

· gene is far from structural genes

. presence of a copy of trpR+ will ___________________

attenuator

The trp structural genes are preceded by a leader

sequence containing another kind of regulatory site called

an _____________

can

Transcription of the leader region of the trp operon _____

occur even when the operon is repressed in the presence

of tryptophan.

Attenuation

______________ is the mechanism by which expression of the

rest of the trp operon is repressed after transcription of the

leader sequence.

tryptophan

The mRNA from leader region can form two different

conformations, depending on the presence or absence of

___________

early termination (attenuation) transcription.

In the presence of tryptophan, the hairpin structures form

in the mRNA and cause ______________________

proceeds to the end of the operon.

In attenuation, the absence of tryptophan, a different hairpin forms and transcription _______________________

simultaneous transcription and translation

Attenuation happens during the __________________________ that occurs in bacteria.

termination of transcription.

In Attenuation, the presence of tryptophan, the ribosome that is

translating the leader mRNA causes __________________

does not interfere with transcription.

In Attenuation, the absence of tryptophan, the ribosome that is

translating leader mRNA _____________________

IN BACTERIA

______________, Attenuation mechanism is common to several operons for enzymes responsible for synthesis of other amino acids.

threonine, histidine, leucine, and phenylalanine.

IN BACTERIA, Attenuation mechanism is common to several operons for enzymes responsible for synthesis of other amino acids.

These include ___________, _____________, ______________, and ___________________

. the larger amount of DNA

. larger number of chromosomes

· spatial separation of transcription and translation

· mRNA processing

· RNA stability

· cellular differentiation in eukaryotes

Gene regulation in eukaryotes is more complex than it is in

prokaryotes because of:

_________________________

_________________________

_________________________

_________________________

_________________________

_________________________

Promoters

· ____________ are nucleotide sequences that bind one or more

proteins that regulate transcription initiation.

. Located immediately adjacent to genes they regulate.

· Specify where transcription begins and the direction of

transcription along the DNA.

Enhancers

· _____________ are nucleotide sequences that can be

upstream, downstream, or within a transcribed gene (cis

regulators).

. Necessary for high level of transcription.

. Control time and tissue specific expression.

. Interact with regulatory proteins (transcription factors).

· Analogous to operators (but more complex).

. Necessary for high level of transcription.

. Control time and tissue specific expression.

. Interact with regulatory proteins (transcription factors).

· Analogous to operators (but more complex).

4 ways that enhancers promote the transcription of a gene

proximal promoter elements

Many promoters contain __________________ that

act to increase the levels of basal transcription.

The CAAT box has a consensus CAAT or CCAAT and is

critical to the promoter's ability to initiate transcription.

CAAT or CCAAT

The CAAT box has a consensus _____ or _______ and is

critical to the promoter's ability to initiate transcription.

EUKARYOTES

the CAAT box only occurs in _________________

lower

Mutations within the promoter sequence dramatically _____ the rate of transcription.

GC box

The ________ is also found in proximal promoter regions

cis

Enhancers are ___ regulatory

cis regulation

Regulation by being located next to the gene being regulated on the same chromosome

Silencers

· ______________ are cis-acting elements that repress the level of transcription.

. Control time and tissue specific expression.

. Interact with regulatory proteins produced by other genes

(transcription factors).

cis-acting

Silencers are ____________ elements that repress the level of transcription.

. Control time and tissue specific expression.

. Interact with regulatory proteins produced by other genes

(transcription factors).

2 ways that silencer repress transcription

Transcription factors

____________________ bind to cis-acting sites and bring

about positive and negative effects on the transcription

initiation rate in response to extracellular signals or in

tissue- or time-specific ways.

extracellular signals or in tissue- or time-specific ways.

Transcription factors bind to cis-acting sites and bring

about positive and negative effects on the transcription

initiation rate in response to _________________ or _____________________________

Chromatin

Initiation of eukaryotic transcription:

. _______________ must be remodeled and modified to allow

transcription proteins to bind to their specific cis-acting

sites.