Gene Control- Prokaryotic Flashcards
how do prokaryotic cells conserve energy and resources?
- only transcribing genes when necessary
a. don’t make mRNA for tryptophan producing enzymes if tryptophan can be absorbed from environment - only producing proteins when needed a. don’t need lactose digesting enzymes if no lactose is present
prokaryotic gene control
Conserves Energy and Resources control enzymes already in cell control production of enzymes negative and positive control operon models regulatory genes
how do prokaryotic cells control enzymes already in the cell
post translation control
1) allosteric enzymes (activated or inhibited)
2) feed back inhibition: end product of anabolic path is the inhibitor
3) adjustment to short term changes
how do prokaryotic cells control of the production of enzymes
transcription control
1) control transcription of genes
2. slower/longer lasting effects: more stable environment
how do they control transcription of genes
a. repressors bind to operators and stop transcription
b. enhancers bind to promotor to speed
transcription
negative control
1) negative slows or stops function
2) feed back inhibition (allosteric enzymes)
3) repressors blocking transcription (gene control)
positive control
1) SPEEDS up production
2) just allowing production does not count!!
3) Enhancers bound to promoter
4) allosteric activators
operon model
clusters of functionally related genes controlled as a group (3 parts)
three parts of operon model
- DNA code for the genes
2) promotor – stretch of DNA before genes
a. attracts RNA polymerase
b. needed to start transcription
3) operator – DNA sequence near promotor
a. binding site for repressor protein
regulatory genes
make repressors found up stream from operon they regulate
trp
tryptophan amino acid
trp operon
1) Repressible operon bcs it is normally active
2) genes make trp
low trp level in cell
operon active
a. repressor is inactive
b. promoter is open to RNA polymerase
c. genes to make trp are copied
high trp level in cell
High trp level in cell : operon repressed
a. trp repressor is allosteric
1. binding to trp activates repressor
2. active repressor binds to operator
3. blocks RNA polymerase
4. genes not transcribed
lactose
(galactose + glucose)
lac operon
Inducible operon : usually off
a. repressor is active unless lactose bound to it
2. genes make
a. β-galactosidase cleaves lactose in 1/2
b. permiase membrane transport protein for lactose
c. third gene
unknown
lac operon in the prescence of lactose
lactose binds to allosteric repressor
1) inactivates repressor
2) Repressor releases operator
3) RNA polymerase copies all 3 genes
positive control of lac operon
- lac operon is an inducible operon = can be activated
- lac operon exhibits positive control = can be speeded up
- If glucose is present E. coli prefer to use it
If glucose is present E coli prefer to use it, process
a. lack of glucose causes E. coli to speed up use of lactose
b. lack of glucose causes build up of cAMP (cyclic AMP) = signal molecule
c. cAMP signals speed up operon translation
d. cAMP binds to regulatory protein CAP
e. build up in glucose in cell causes lack of cAMP so CAP becomes inactivated
what happens when cAMP binds to regulatory protein cap
I. CAP becomes active
ii. CAP binds to start of promotor
iii. Makes promotor more attractive to RNA
polymerase
repressible operons
a) repressor inactive w/o allosteric binding
b) normally on
c) usually anabolic
inductible operons
a) repressor active unless bound
b) normally off
c) usually catabolic
