regulation of transcription

what does the activator do?

enhances interaction between RNA polymerase and promoter region

encourages expression of gene

what is the function of the promoter region?

where RNA polymerase binds to DNA

what is the function of an operator?

sequence of DNA where transcription factor binds

what does a repressor do?

protein that impedes the progress of RNA polymerase along the template strand, impeding the expression of a gene

bind to silence/ operator (operator mainly in prokaryotes)

what does an enhancer do?

bound to by activators to loop DNA to bring a specific promoter to the initiation complex

what are silencers?

regions of DNA bound by repressor proteins to silence gene expression

prevents RNA polymerase from binding to promoter region

what are general transcription factors (GTF)?

class of proteins that bind to specific sites on DNA to activate transcription

found in prokaryotes

what is the basic transcription apparatus in prokaryotes?

GTFs, RNA polymerase, mediator multiple protein complex

what is the lac operon?

found in E.coli

operon of genes involved in lactose metabolism

operon is only expressed when lactose is present and glucose is low/absent

what are the two regulators for the operon?

lac repressor and catabolite activator protein (CAP)

what does the lac repressor do?

represses the operon but stops acting as a repressor when lactose is present

senses lactose indirectly through the isomer, allolactose

what does the catabolite activator protein do?

activates the transcription of the lac operon only when glucose levels are low

detects glucose indirectly through cAMP molecule

what are the three genes in the operon?

lacZ, lacY, LacA

what is the additional gene that is used but is not in the lac operon?

Lac I

what does Lac Z do?

codes for beta galactosidase (lactose → glucose + galactose)

what does Lac Y code for

lactose permease (transports lactose across membrane)

what does lac A code for?

• encodes thiogalactoside transacetylase

• removes toxic thiogalactosides from cell

what does Lac I do?

• encodes repressor molecule which regulates operon by binding to operator region

how does the lactose repressor act when there is no lactose

• binds tightly to operator

• prevents transcription

how does the lactose repressor act when there is lactose present

• allolactose binds to repressor causing a conformational change

• causes repressor to dissociate from operator

• allolactose is acting as an inducer (so lac operon is an inducible operon)

• transcription occurs

how does CAP act when there are low glucose levels?

• cAMP is produced and binds to CAP causing conformational chage

• CAP can now bind to CAP site

• CAP helps RNA polymerase to bind to promoter

• transcription is upregulated

how does CAP act when there are high glucose levels?

• no cAMP made

• CAP cannot bind to CAP site

• transcription continues at a basal level

what is the purpose of the lac operon?

ensures that bacteria only turn on lac operon once glucose has been used up

how does gene regulation in eukaryotes occur?

control of which genes in the genome are expressed by different cells

different patterns of gene expression in each cell allowing diverse structures and functions

how to general transcription factors work in eukaryotes?

TFs bind to certain sequences of DNA triggering transcription

how do additional transcription factors work in eukaryotes?

determine when and where a gene is used. They act as "switches," binding to specific DNA regions to start or stop gene activity

tissue specific gene expression

example: albumin

• activators are tissue specific

• activators for albumin are usually found in the liver therefore elevated levels of albumin transcription occur in the liver