chapter eighteen part one Flashcards
gene regulation in prokaryotes/unicellular eukaryotes
respond to different environmental cues
- feedback inhibition
- adjust activity of enzymes already present
- adjust production level of certain enzymes
gene regulation in multicellular eukaryotes
- environmental cues
- developmental changes
- cell specialization/differentiation
- expression of different genes in certain areas
sites of gene regulation
- transcription regulation
- chromatin modification
- transcription initiation - post-transcriptional regulation
- alternative RNA splicing
- mRNA degradation
- mRNA location/availability - post-translational regulation
- regulate protein activity (constitutive, regulated)
- regulate protein lifespan
where odes the most regulation occur
transcription regulation
- often in response to signalsc
chromatin modification
- DNA methylation - methylated regions where genes no expressed
- histone protein methylation - condenses chromatin and reduces transcription
- histone protein acetylation - addition of acetyl group to AA in histone tail loosens chromatin and promotes transcription
transcription initiation
- key control point
- involves proteins that bind to DNA and inhibit/facilitate binding of RNA poly
- can vary in cell/tissue type
alternative RNA splicing
from single pre-mRNA, multiple mRNA
- troponin (muscle protein)
- plasma B cell
mRNA degradation
by enzymes
- hemoglobin mRNA in erythroblasts
- mRNAs usually stable for a while, translated repeatedly into red blood cells
regulation of protein activity
reversible addition of phosphate groups. acquired sugars, transported to target destinations
- constitutive enzymes
- regulated enzymes
constitutive enzymes
always there
- glycolysis, aminoacyl-tRNA synthetase
- most of bacterial enzymes, varies by cell type for multicellular euks
regulated enzymes
inducible - on/off
- digestive/biosynthetic/cyclins
- fewer of bacterial enzymes, varies B cell type for multicellular euks
operon
collection of several genes for one biosynthetic pathway and its regulatory regions
regulatory regions of operon
promoter, operator, activator binding sites
promoter
site for RNA poly to bind and begin transcription
operator
controls access of RNA poly to genes
- where repressor proteins bind
operons under negative control
use a repressor protein
1. repressible
2. inducible
repressible operon (trp)
- anabolic enzymes
- by itself, trp operon turned on
if no trp
operon turned on, repressor protein inactive, transcription of enzymes needed for trp synthesis produced
if trp
operon off, trp binds to repressor (corepressor), repressor binds to operator, RNA pol access to promoter blocked, no enzymes for trp synthesis produced
inducible operon (negative control) (lac)
- catabolic enzymes (using lactose as energy source)
if no lac
operon turned off
- regulator produces repressor protein
- repressor by itself binds to operator
- RNA poly blocked, no enzymes for lac catabolism
if lac
operon turned on
- lac binds to repressor protein (lac = inducer)
- repressor protein moved from operator/can’t bind
- RNA poly proceeds, enzymes for lac catabolism transcribed
operons under positive control
- use activator protein
- inducible
inducible (positive control) (lac)
- lac operon fine-tuned by being sensitive to glucose concentration
- if glucose low, then cAMP goes up and cAMP binds to CRP
- if glucose high, cAMP concentration falls, CPR detaches from lac operon
what happened when cAMP binds to CRP
- it binds to DNA, increases tcr of lac operon
