Control of Gene Expression in Bacteria

Question 1

constitutively expressed genes

Answer 1

genes that specify essential products that are continuously expressed

Question 2

inducible and repressible genes

Answer 2

regulatory mechanosms allow synthesis of products that are only required under certain conditions by inducing or shutting them down

Question 3

what is an operon?

Answer 3

group of structural genes and sequences that control transcription

promoter, operator, gene a, b, c

Question 4

what is an operator?

Answer 4

part of operon that determines whether transcription will occur

overlaps with 3’ end of promoter and 5’ end of first structural gene

what the regulatory protein may bind to

Question 5

negative inducible operon

Answer 5

transcription must be turned on

-regulator gene encodes for repressor protein
-is bound to operator and prevents RNA polymerase from binding to promoter
-inducer binds to the repressor to inactivate it
-RNA polymerase now free to bind and activate transcription

Question 6

negative repressor operon

Answer 6

transcription must be turned off

-co-repressor binds to repressor protein so it can bind to operator
-inhibits transcription

Question 7

what is positive control?

Answer 7

-regulatory protein is an activator that binds to operator and starts transcription

-alternatively, activator can bind upstream of operator to influence transcription
ex: CAP is an activator that binds upstream of promoter and enhances binding of RNA polymerase to promoter

Question 8

lac operon

Answer 8

negative inducible
-regulator protei is inhibitor
-allolactose inactivates inhibitor (inducer)

positive control
-CAP and cAMP enhances transcription

Question 9

lac operon when lactose is present

Answer 9

-lactose transports into cell by permease
-lacZ breaks it into glucose and galactose
-converts into allolactose which keeps operator on the on switch
-RNA polymerase binds to promoter and induces expression of 3 structural genes

Question 10

lac operon when lactose is absent

Answer 10

-repressor protein (lacl) binds to operator (lacO)

Question 11

catabolite repression

Answer 11

bacteria turning off other metabolic pathways when glucose is present (more favourable)

Question 12

positive control and methods

Answer 12

transcription of other metabolic pathways turned on when glucose is low

cAMP binds upstream of promoter

When glucose is low
-cAMP levels high, binds to CAP , complex binds to DNA which increases efficiency of polyemrase binding

when glucose is high
-cAMPS levels low, does not bind to CAP