Lectures 1-3

Question 1

Describe transport proteins.

Answer 1

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.

Question 2

What is facilitated diffusion?

Answer 2

passive transport

Question 3

describe the sodium pump

Answer 3

primary active transport.
3 Na+ out, 2K+ in
Uses energy from breaking down ATP to move them.

Question 4

what is secondary active transport?

Answer 4

doesn’t use ATP.

Question 5

Describe ion channels.

Answer 5

only passive transport, high to low.
transmembrane proteins (interact with lipid, embedded in membrane)
selective permeability.
the opening is controlled somehow.
diverse

Question 6

Describe selective permeability.

Answer 6

selectivity filter determines what ions may pass through.
usually only cations or anions.
discriminates based on charge or size.

Question 7

what is depolarisation/hyper polarisation?

Answer 7

depolarisation - increase in voltage

Question 8

Describe gating.

Answer 8

Most are closed, so deal with mechanism for opening it.

mechanically gated,
second messengers,
phosphorylated,
temperature,
ligand gated,
voltage gated,
proton gated.

Question 9

how are ion channels named?

Answer 9

voltage gated/sensitive __ channel.

ligand channel named after neurotransmitter that open or closes it.

Question 10

Describe the mechanism of a ligand gated ion channels.

Answer 10

neurotransmitter binds and the channel changes its shape so the pore can open up and the ligand can pass through.

Question 11

Describe the muscle nicotinic receptor.

Answer 11

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.

Question 12

Describe voltage gated channels.

Answer 12

change in voltage opens it, usually depolarisation.

na/ca/k channels. all similar structures.

Question 13

Describe the structure of a K channel

Answer 13

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

Question 14

Describe the structure of Na/Ca channels.

Answer 14

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.

Question 15

Where are nuclear hormone receptors?

How do they bind to ligands?

Answer 15

intracellular, bind to lipid soluble compounds allows them to cross the cell membrane and bind to receptors inside the cell

Question 16

What is transactivation?

Answer 16

NHR dimer binds to transcription factors.
activates genes, increases RNA and protein translation.
Hormone responsive element, binds transcription factors to NHR dimers.

Question 17

What is transrepression?

Answer 17

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.

Question 18

Describe the mechanism of nuclear hormone receptors.

Answer 18

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.

Question 19

What are gene protein coupled receptors.

What are their structure?

Answer 19

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.

Question 20

Describe the G protein coupled receptor structure and general mechanism.

Answer 20

agonist binds to GPCR, which couples itself with the G protein.
G protein interacts with an effector/target protein which produces second messenger.

Question 21

Describe a G protein.

Answer 21

3 subunits.
Alpha - bound to GDP
beta
gamma

Question 22

describe the specific mechanism of a GPCR

Answer 22

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.

Question 23

What is cAMP?

Answer 23

a target molecule, nucleotide.
coupled to many molecules, ie dopamine, noradrenaline.
2 halves, some inhibit, some stimulate.

made by adenylate cyclase.

Question 24

what is Gs?

Answer 24

G stimulation.

Question 25

What is cAMP’s main effect?

Answer 25

switch an inactive kinase to an active one, kinases phosphorylate things.

also inactives myosin light chain kinase, relaxes smooth muscle.

Question 26

What is Gi?

Answer 26

inhibitory.

slows down cAMP production.

Question 27

What is the phospholipase C pathway/IP3 pathway?

Answer 27

Gq (G protein) interacts with phospholipase C (breaks down phospholipids)
splits PIP2 into DAG and IP3.
Both are secondary messengers.

DAG interacts with protein kinase C,
IP3 goes to the endoplasmic reticulum, causes release of calcium, which acts as a messenging molecule.

Question 28

What is PIP2, IP3 and DAG?

Answer 28

PIP2: phosphatidylinositol bis phosphate; IP3: inositol trisphosphate; DAG: diacylglycerol

Question 29

What are orphan receptors?

Answer 29

no known ligands. 30NHR are orphans.

Question 30

first drug?

Answer 30

Paul Ehrlich

Salvarsan