Lectures 1-3 Flashcards
Describe transport proteins.
Passive transport, down conc gradient.
Active transport, up conc gradient, requires ATP.
A protein sits in the lipid bilayer, needs AA that can easily interact with lipids - lipid soluble.
Binding site for substrate, travels through the membrane and is released on the other side.
What is facilitated diffusion?
passive transport
describe the sodium pump
primary active transport.
3 Na+ out, 2K+ in
Uses energy from breaking down ATP to move them.
what is secondary active transport?
doesn’t use ATP.
Describe ion channels.
only passive transport, high to low. transmembrane proteins (interact with lipid, embedded in membrane) selective permeability. the opening is controlled somehow. diverse
Describe selective permeability.
selectivity filter determines what ions may pass through.
usually only cations or anions.
discriminates based on charge or size.
what is depolarisation/hyper polarisation?
depolarisation - increase in voltage
Describe gating.
Most are closed, so deal with mechanism for opening it.
mechanically gated, second messengers, phosphorylated, temperature, ligand gated, voltage gated, proton gated.
how are ion channels named?
voltage gated/sensitive __ channel.
ligand channel named after neurotransmitter that open or closes it.
Describe the mechanism of a ligand gated ion channels.
neurotransmitter binds and the channel changes its shape so the pore can open up and the ligand can pass through.
Describe the muscle nicotinic receptor.
4 transmembrane domains, large extracellular bit, big intracellular loop between 3 and 4.
helps the cell regulate the protein.
present in the muscle, nicotine agonist for it.
Describe voltage gated channels.
change in voltage opens it, usually depolarisation.
na/ca/k channels. all similar structures.
Describe the structure of a K channel
4 seperate subunits come together.
Each subunit has 6 transmembrane domains.
4th one has charges on it and acts as the voltage sensor. moves when voltage changes, changes structure
Describe the structure of Na/Ca channels.
4 subunits are linked together into one long protein.
“psuedo subunits” since not really seperate, but behave as if they are.
Alpha subunit can form a channel on its own, Beta are accessory subunits.
Where are nuclear hormone receptors?
How do they bind to ligands?
intracellular, bind to lipid soluble compounds allows them to cross the cell membrane and bind to receptors inside the cell
What is transactivation?
NHR dimer binds to transcription factors.
activates genes, increases RNA and protein translation.
Hormone responsive element, binds transcription factors to NHR dimers.
What is transrepression?
shutting genes off, reduces expression of a protein.
NHR receptor monomer from earlier that didn’t dimalise.
bind to transcription factors and stop them interacting with DNA.
or inhibit TF once it’s bound to DNA.
Describe the mechanism of nuclear hormone receptors.
steroid diffuses through the cell membrane to the cytoplasm and joins a monomer receptor which is joined to a heat shock protein.
the two dissociates, and two receptors form a pair, they then enter the nucleus via a nuclear pore.
It then interacts with DNA, switching genes on or off.
Slow form of signalling.
What are gene protein coupled receptors.
What are their structure?
very diverse and important.
7 transmembrane domains.
start outside the cell, finish inside.
G protein is seperate, binds to large intracellular loop between 5th and 6th domain.
Describe the G protein coupled receptor structure and general mechanism.
agonist binds to GPCR, which couples itself with the G protein.
G protein interacts with an effector/target protein which produces second messenger.
Describe a G protein.
3 subunits.
Alpha - bound to GDP
beta
gamma
describe the specific mechanism of a GPCR
agonist binds to a receptor, GPCR changes shape and allows it to bind to the G protein.
GTP replaces GDP to alpha.
changes shape of G protein, splits into alpha with GTP and beta/gamma.
alpha interacts with a target protein.
alpha has built in GTPase, breaks down GTP to GDP and pi.
joins back to start.
What is cAMP?
a target molecule, nucleotide.
coupled to many molecules, ie dopamine, noradrenaline.
2 halves, some inhibit, some stimulate.
made by adenylate cyclase.
what is Gs?
G stimulation.
