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lecture 18 Flashcards

(25 cards)

1
Q

bacteria that undergo ____ transcription have no ___ genes

A

constitutive transcription

regulatory genes

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2
Q

regulation of bacterial genes is the predominant mode that takes place in what 2 levels?

A

regulates initiation of transcription & amount of transcription

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3
Q

what is negative transcription control?
what is positive transcription control?

A

binding of repressor to regulatory DNA sequence— preventing transcription

binding of activator protein to reg DNA, result of initiating gene transcription

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4
Q

what are repressor proteins and what do they bind to?
what does it do to polymerase?
what are the 2 active sites on it?

A

exert negative control on transcription when they are active and bind to the repressor

binds on reg DNA where the polymerase would bind OR by preventing the transcription complex

DNa binding domain– locating & binding operator DNA
allosteric domain— binds a molecule & changes conformation

inactivated by inducer binding to allosteric site

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5
Q

what may some repressors need to activate DNA bidding site?

A

corepressor

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6
Q

what is positive control of transcription controlled by?
what do activators do?
what site do they have?

A

activator proteins that bind on activator binding sites
OR
Bind to repressors which make them disassociate

binding to repressor makes it leave & allows RNA pol binding at the promoter & intimate transcription

DNA binding site

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7
Q

some activators need a ____ to activate the DNA binding domain, then ___ happens, allowing for binding to DNA

A

allosteric effector compound

allosteric change

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8
Q

what happens if activator binds an inhibitor?

A

will not bind to DNA

OR
If a repressor, will unbind from DNA

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9
Q

what is a common shape of DNA reg proteins?
what 2 protein segments contact the DNA?
what is the most common structural motif in bacteria?

A

a helices

-single poly peptide folds to form 2 domains that bind specifically
-reg protein consists of 2 or more polypeptides joined to form a dimer or trimer or more

helix turn helix motif–> 2 alpha helices fit into the major groove of DNA

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10
Q

what are operons ?

A

genes that are undergoing transcriptional regulation by shared regulatory region

-contain additional regulatory DNA sequences that interact with promoters to exert control

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11
Q

what does glycolysis of glucose produce?
how is lactose made into glucose?

A

pyruvaqate + ATP

-B galactosidase breaks the B galactoside link to get glucose + galactose

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12
Q

what are the functions of B galactosidase ?

A

break lactose to glucose + galactose

convert lactose to allolactose– important in regulating transcription of lac operon—-> acts as inducer

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13
Q

what are the regulatory components of the lac operon?

A

promoter– contains -10 and -35 sites
operator—> lacO–> binds repressor, +1
CAP binding site, on promoter

+++ all partially overlap+++

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14
Q

what are the structural genes of the lac operon and what do they do?

A

lacz— encodes B galatosidase

lacY—encodes permease, which allows lactose to enter the cell

lac A—transacetylase– not essential for metabolism

Lacl: the repressive

are transcribed as polycistronic mRNA

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15
Q

when does the lac operon function?

A

when no glucose is available and when lactose is there

if lots of gluecose— repressor bound to the operator

if lots of lactose and NOT glucose—allolactose, which is the inducer, binds the repressor— which makes it unbind the operator, so we have transcription
CAP-cAMP must also bind to CAP binding site

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16
Q

when glucose is available, what is low? what if it is high, what are cAMP levels like?

A

cAMP–> so not CAP( activator)-cAMP (coactivator) can form and bind to the sit to help with initiation

high cAMP to bind CAP-cAMP–> binds at site & transcription begins

17
Q

what is catabolite repression?

A

glucose blocks transcription even when lactose is present

the preferred catabolite –> glucose–> represses transcription

18
Q

which two complementation groups formed that lac- mutants formed?
what are polar mutations ???

A

lacZ ( b galactosidase) and lacY (permease)

in lacZ– reduces or preventing translation of other genes sequences in the transcript due to the Shino Dalgrano sequence

19
Q

what are cis acting factors?
what is cis dominant?

A

only affect gene expression in the same piece of DNA squence– do not diffuse

ex: promotor, operator

  • the only genes the operator is able to influence are the genes located downstream on the same gene
20
Q

what are trans acting factors?

A

capable of influencing the expression of genes on other chromosomes
- can diffuse and bind to another target

ex: proteins— repressor, activator

21
Q

what are the conditions that take place only when glucose is depleted and lactose is present?

A

cAMP levels rise

CAP-cAMP formation– ->which binds to CAP region on lac promotor

allolactose is produced

repressor protein is modified by allolactose, making it release from the operator, allowing transcription

22
Q

when does basal transcription occur?

A

both glucose and lactose is present

23
Q

What are characteristics of lac superepressor?

A

Can’t bind inducer molecule
Always binds the operator
Gain of function dom mutation

24
Q

What is catabolic repression mediated by?

A

Activator protein binds to promoter
OR
sugar kept out of cell by inactivating permease

25
What is the lacl tetramer?
2 sub bind to O1 2 bind to 02 or 03