negative
gene regulation: ____ control- inhibition of trancription by repressor
positive
gene regulation: ___ control- enhancement of transcription by activator
bacterial gene regulation
few regulatory controls for multiple structural genes
eukaryote gene regulation
multiple regulatory controls for single structural genes
operons
bacterial gene expression is based on ____
operon
unit of gene regulation for multiple structural genes that are linked and functionally related
inducible
system usually off, controlled by turning on
repressible
system usually on, controlled by turning off
lactose (lac) operon
inducible, for catabolism of lactose
tryptophan (trp) operon
repressible, for anabolism of tryptophan
Pi
promoter for repressor (i) gene
i
structural (protein coding) gene for allosteric repressor protein
Plac
promoter for lac operon proper
o
operator, where repressor can bind for negative control
z, y and a
three structural genes for lactose metabolism
1. z
for B-galactosidase, enzyme for above biochemical reaction
2. y
for permease, enzyme that increases permeability of cell membrane to lactose
3. a
for transacetylase, enzyme whoe exact function remains unclear
1. repressor
allosteric protein w both an allosteric site and active site
active site
pocket within the repressor which allows it to bind to the operator
allosteric site
second pocket of repressor, where lactose can bind to inhibit the binding of the repressor to the operator
rna polymerase (pol)
recognizes and binds to promoters to initiate transcription of their structural genes
off
when lactose is absent, operon is ___ as theres no substrate to metabolize
Pr
promoter for repressor (R) gene
R
structural gene for allosteric repressor protein
Ptrp
promoter for trp operon proper
o
operator, where repressor can bind for negative control
e, d, c, b, and a
5 structural genes for tryptophan synthesis
on
when tryptophan is absent, trp operon is __ as enzymes are needed to synthesize tryptophan
1. more space and time
2. much larger genomes
3. more complicated cells
why is gene regulation more complex in eukaryotes than bacteria
eukaryotes
operons are rare in
Trancriptional Control
analogous to that of bacterial operons
epigenetics
gene regulation by modifying the chemical state of the chromatin
chromatin
chromosomal material
cis elements
specific dna sequences to which trans elements can bind to regulate the expression of the linked gene
1. promoters
special dna sequences to which rna polymerase can recognize, bind and initiate transcription of the gene
2. enhancers
specific dna sequences to which trans factors can bind to increase transcription of the gene
3. silencers
specific dna sequences to which trans factors can bind to inhibit transcription of the gene
1. promoters
2. enhancers
3. silencers
3 cis elements
1. rna polymerase
2. transcription factors
2 trans elements
trans elements
diffusible regulatory proteins that bind to specifix elements to control the linked gene
rna polymerase
enzyme that recognizes and binds to promoter to initiate transcription of the associated linked gene
transcription factors
dna binding regulatory proteins that bind to cis elements to increase or decrease transcription of the linked gene
dna looping model
how different enhancers and TFs are brought into close proximity of a promoter to initiate transcription of a gene
short and far
in dna looping model, promoters are a ___ distance from gene and enhancers are ___ from gene
epigenetics
gene regulation via changes to the chemical state of the chromatin
1. euchromatin - potentially active
2. heterochromatin - usually inactive
two chromatin states
1. constitutive heterochromatin - always heterochromatin
2. facultative heterchromatin - can become euchromatin and vice versa
two heterochromatin states
dna methylation
addition of methyl groups to dna
histone acetylation
addition of acetyl groups to histones, which are the major proteins of eukaryotic chromosomes
-methylated DNA
-deacetylated histones
-tightly coiled dna
-enzyme inaccessible
-usually inactive
5 facts about facultative heterochromatin
-demethylated dna
-acetylated histones
-loosely coiled dna
-enzyme accessibke
-potentially active
5 facts about euchromatin