Ch 16- Gene Control in Prokaryotes

OB Domain

DNA Binding Protein responsible for binding to DNA and forming H bonds

Operon

promoter + operator + structural genes

Where do the regulatory protein bind to in an operon?

the operator

Regulatory proteins

binds to the operon and stimulates transcription (+ control) or represses transcription (- control)

Types of regulatory elements

positive control

negative control

Positive control

regulatory protein enhances gene expression

Negative control

regulatory protein inhibits gene expression

Negative control operons

inducible

repressible

Inducible

turned off but it needs to be on

neg inducible element prevents repressor regulatory protein from binding to gene, allowing gene to be on

Lac operon

negative inducible operon

Reg protein turns off, but presence of Lac turns on

= production of glucose

Repressible

turned on but it needs to be turned off

regulatory protein binds to operator with repressor element and represses transcription

regulatory protein cant bind without neg repressible element

Positive control operons

stimulate transcription

catabolite repression

Catabolite repression

availability of glucose turns other genes off

resulting in no transcription

cAMP and CAP bind upstream

More glucose=

less cAMP

CAP is not on operon

equals no transcription

Lower glucose=

more cAMP

results in cAMP binding to CAP and stimulates transcription

Increased v decreased glucose

Increased—no translation

Decreased—translation

Attenuation

premature termination of transcription

transcription begins, but structural genes are not transcribed

Attenuator

more tryptophan

Terminates transcription

Antitermination

decrease tryptophan

does not terminate transcription

Bacterial enhancers

increases transcription, can be distant from the enhancer

Antisense RNA

complementary to targeted sequence of mRNA

can’t produce the protein bc it blocks the translation

Riboswitches

formation of secondary structures in mRNA

Ribozymes

mRNA enzymes leading to cleavage and degradation