Bio - Regulation of Gene Expression

operon

cluster related genes w/ on/off switch

3 parts of an operon

1. promotor: where RNA polymerase attaches

2. operator: “on/off”/ control access of RNA polymerase

3. genes: code for related enzymes in a pathway

regulatory gene

1. produces repressor protein

2. it’ll bind to the operator to block RNA polymerase

repressible operon

1. normally on

2. anabolic (builds organic molecules

3. organic molecule product acts as a corepressor

   1. bind ot the repressor to activiate it

   2. turns off the operon

4. ex. trp open

inducible operon

1. normally off

2. catabolic (break down food for energy)

3. repressor is active

   1. inducer binds to the repressor

   2. this inactivates the repressor

   3. this turns on the operon

4. ex lac operon

positive gene regulation

1. speeds up transcription

2. involves catabolite activator protein (CAP)

   1. a regulatory protein

   2. an activator of transcription

   3. activated when cyclic amp attaches

      1. produced when glucose is scarce

3. activate CAP attaches to the promotor of the lac operon

   1. increasing the affinity of RNA polymerase

   2. thus accelerating transcription

4. CAP detaches from the lac operon

   1. when glucose lvls increase

   2. transcriptions returns to a normal rate

differential gene expression

1. in a typical human cell only 20% genes are expressed at any given time

2. different cell types (w/ identical genomes) turn on different genes to carry out specific func

3. this accounts for the differences between cell types

chromatin struct

tightly bound DNA has less genes accessible transcription

DNA methylation

1. added to dna

2. makes them more tightly packed

3. decreases transcription

histone acetylation

1. acetyl groups added to9 positively charged lysine in the histone tails

2. makes dna more loose

3. increases transcription

epigenetic inheritance

1. modification on chromatin can be passed on to future generations

2. ex. genomic imprinting, DNA methylation, histone acetylation

3. unlike DNA mutations, these changes to chromatin can be reverse (de-methylation of DNA)

4. explains difference between identical twins

transcription initiation

1. control elements

   1. segments of noncoding dna that help regulate transcription

   2. bind transcription factors which initiate transcription

2. enhances gene expression

3. transcription facotrs

   1. general proteins needed ot start transcritpion

   2. binds w/ other proteins within the promotor or TATA box

   3. specific transction facotr: proximal control elemetns are located close ot the promotor

   4. enhancer

      1. distal contorl elements

      2. may be far from gene or even located in an intron

   5. activator

      1. a protein that binds ot an enhancert

      2. stimulates transcription o fa gene

      3. bound actiators cause mediator proteins to intereact w/ proteins at the promotor

alternative RNA splicing

1. diff mRNA molcules produce from some primary transcript

2. depends on which RNA segments treated as exons and introns

mRNA degradation

1. the life span of mRAN molecules in cytoplasm is key determining protein syn

2. eukaryotic mRNA more long live than prokary

initiation of translation

1. slected mRNAs can be blocked by regulatory proteins that bidn to sequences or struct of the mRNA

2. translation initiation factors simutaneously activated in egg follwoing fertilzation