gene expression regulation Flashcards
central dogma
the concept that cells follow a particular direction/flow of genetic information
genes provide the information for making proteins —> genes move from DNA —> RNA —> proteins
transcription makes pre-mrna/mrna
translation —> creates polypeptide genes (proteins)
difference between transcription and translation in prokaryotes and eukaryotes
location that they occur
prokaryotes—> cytoplasm bc they don’t have a nucleus
eukaryotes—> transcription occurs in nucleus and translation occurs in the cytoplasm
nearly all cells in your body have the same DNA.. how
we start from a single cell, and DNA from that cell gets copied every time we make a new cell
how can two cells with the same set of genes function differently
gene regulation
gene regulation
process of turning on/off different genes when they are needed
— occurs due to both internal and external environment of the cell
where does most gene regulation occur in prokaryotes and eukaryotes
happens in transcription
however for eukaryotes gene regulation occurs in many other steps as well
differential gene expression
allows certain cells to be or to not be expressed based on needs
transcription factors
proteins that bind to dna sequence and initiate transcription
rna polymerase II
protein that pulls apart 2 dna strands and joins RNA nucleotides complementary to the dna template strand
transcription regulation involves transcription factors that exert negative or positive control
what are two types of transcription factors
repressor protein
activator protein
repressor protein
binds to dna and decreases(or inhibits) the rate of transcription
negative control
activator protein
binds to dna and increases the rate of transcription
positive control
small effector molecules
binds to repressor and causes conformational change
impacts whether or not regulatory transcription factor can bind to DNA
sometimes acts as inducer core press or
prokaryotic gene regulation parts
operon ( containing two or more structural genes, promoter, and operator) and regulatory genes
operon
made up of two or more structural genes, promoter, and operator
structural genes
get transcribed and get turned into proteins
their gene products lead to cellular structures/proteins
promoter
controls where/when transcription occurs
operator
regulatory dna sequence like an on/off switch
regulatory genes
regulate gene expression
encodes gene products that regulate gene expression
organization of lac operon
contains a lac promoter(lacP), lac operator(lacO), and lac genes(lacZ,lacY, lacA)
what do lac genes in lac operon do
they encode for proteins that break down lactose when transcribed
lac regulatory gene
lacl
encodes lac repressor
has its own promoter (i promoter)
example of negative control
lac operon with a repressor protein
how does the presence/ absence of lactose affect the lac operon
when lactose is absent, the lac repressor binds to the operator and transcription is blocked
when lactose is present, the lac repressor is released from the operator and transcription proceeds at a slow rate
why does transcription occur when lactose is present
in its presence, allolactose(small effector molecule) is made and binds to the lac repressor, preventing it from binding to the operator and transcription proceeds
inducible operon
usually off but can be stimulated (induced) to turn on when a specific small molecule interacts with the repressor protein
lac operon with a repressor protein q
example of positive control
lac operon with an activator protein
E.Coli
what does e.coli use to determine its activity
glucose and lactose
when glucose and lactose are both present in the environment, bacteria prefers glucose
when lactose is present, and glucose conc. is low, then bacteria uses lactose
Catabolite activator protein CAP
an activator of lac operon
also known as cAMP receptor protein
CRP
cAMP
small effector molecule
controls CAP
accumulates when glucose is low
how does cAMP regulate transcription
when cAMP binds to CAP, complex binds to CAP site near the lac promoter, which increases RNA polymerase binding and transcription occurs
glucose conc. levels effects on cAMP
when glucose is low, cAMP increases
when glucose is high, cAMP decreases
when lactose is present and glucose is low
the lac operon is turned on
abundant lac mRNA is synthesized
cAMP levels will be high and CRP is active
CRP binds to CRP-binding site, and the cAMP-CRP complex stimulates the RNA polymerase binding to the promoter, increasing transcription
when lactose and glucose are present, the lac operon
is turned on but is working less
cAMP levels will be low, then CRP is inactive
less CRP binds to the site so RNA polymerase less likely to bind to the promoter, leading to lower transcription rates
example of negative control: trp operon with a repressor protein
what does trp operon do
trp—> tryptophan amino acid
repressive operon
builds things up unlike lac operon
biosynthesizes
in the absence of tryptophan what occurs to trp operon
the trp repressor dissociates from the operator and RNA synthesis proceeds
when tryptophan is present..
the trp repressor binds the operator and RNA synthesis is blocked
repressible operon
usually on, but can be inhibited(repressed) when specific small molecules interact with the repressor
trp how it works
O= operator
P = promoter
trpR = trp regulatory gene
when tryptophan is low, trp repressor is inactive and can’t bind to operator site, trp operon transcription occurs
when tryptophan is present, trp repressor is activated and binds to operator site, and trp operon stops which inhibits transcription
