Bio 2 - Prokaryotic Gene Expression

Exam 2

Prokaryotes

no structural diversity, metabolically diverse

photoheterotrophy

carbo

chemoautotrophy

carbon + energy from inorganic chemicals

extremophiles

survive in temps above boiling point, high salinity content, ph 1 (South Pacific giar - bacteria hibernated and paused life)

selective gene expression

conserve energy and resources

pre transcriptionally

most efficient (stops translation all together)

post transcriptionally

deactivate made mRNA

post translational

fastest - catabolize or deactivate proteins

Operon

group of genes controlled by one promoter

Promoters

binding sites for polymerase (strong = exact sequence/strong bind weak =sequence doesn’t line up quite right)

Sigma factors

help polymerase do its job + can promote multiple operons

Inducer

stimulate synthesis of a protein

Operators

sites of binding for other proteins

negative control

repressor - binds to operator + down regulates transcription

positive control

activator - binds to operator + up regulates transcription

Lac operon

inducible system (normally off), controls lactose metabolism in E coli

Z gene

B galactosidase

Y gene

B galactoside permease

A gene

B galactoside transacytelase

Lac repressor protein

binds to multiple operators to prevent transcription - negative regulation (creates hair pin loop so RNA pol can’t bind)

TRP operon

repressible system - creates proteins + tryptophan, new tryptophan binds to repressor stopping transcription

Describe the state of both the lac repressor protein and CRP as well as the outcome of the lac operon system for each of the following scenarios:
   A. lactose but no glucose present
   B. glucose but no lactose present
   C.  both glucose and lactose present
   D. neither glucose nor lactose present

A. Lactose present means that the lac repressor protein will be inhibited by allolactose, and transcription will occur. Since transcription will occur, and there is no glucose, cAMP levels can rise, activating CRP, leading to the up regulation of transcription of the lac operon.

B. If glucose is present, then the production of cAMP is halted, therefore no production of CRP and no up regulation of transcription. With no lactose present, the lac repressor protein can bind to polymerase, inhibiting it from completing transcription. 

C. If lactose is present, the lac repressor protein will be inhibited by allolactose, allowing for transcription to occur. But if there is glucose present, no cAMP, no CRP, and no up regulation of transcription. In this scenario, transcription would occur but in very small amounts.

D. If there is no lactose present, the lac repressor protein is active and binding to RNA polymerase, preventing transcription. But, if there is also no glucose present, cAMP is binding to CRP which is meant to up regulate transcription and activate RNA polymerase once again. But because the lac repressor is bound, it will still out-prevent CRP from binding and no transcription will occur.