pharmacology Flashcards
What does intracellular binding describe?
Hint - which set of stairs is involved in every single secondary messenger system?
ligand + receptor binding → enzyme cascade activation → cellular response/s
What do receptors allow?
Hint - signals + intracellular or extracellular change
- extracellular signals across PM to respond to stimuli
- so extracellular substances (can’t pass through) → intracellular change
Which molecular responses can receptors allow?
Hint - 2 are very cellular, one to do with channels and one to do with +VE feedback
- opening of ion channels
- secretion of other signalling molecules
- cell motility (movement)
- modification of cell cycle
What type of signalling is utilised by type 2 and type 3 receptors?
- type 2 receptors → G-protein pathway
- type 3 receptors → enzyme-linked cell surface pathway
Describe type 1 receptors.
Hint - type of transmission, what its coupled to how many times its repeated
- associated w/ fast neurotransmission (GABA, 5-HT, ACh)
- receptors are coupled to ion channels and sit on the cell membrane like subunit
- subunits repeated 4/5x within membrane
What is a ‘binding domain?’
where small molecule (substrates) will bind
Describe the example of type 1 nicotinic ACh receptors (stimulatory) and how they work.
- consists of 5 membrane spanning subunits: • 2 x α (binding domain for ACh) • β • γ • δ 1. 2x ACh molecules bind to 2 alpha units 2. opens ligand-gated Na+ ion 3. depolarises cell as influx of Na+
Describe type 2 receptors and how they work.
Hint - 4/5 → ligand binds domain, signal transmitted, domain + signalling molecule and GP activation
- single polypeptide chain (400-500 AA residues)
- ligand attaches to binding domain → signal travels through chain → signalling molecule (receptor) binds to domain → G-protein activated
Draw, label and describe the structure of a type 2 receptor.
Hint - looks like the piping of plumbing in the house
- receptor protein forms seven transmembrane α-helices embedded in membrane
- long intracellular (3rd) loop between α-domains 5 and 6 where G protein couples to receptor
(see notes for diagram)
Describe G-proteins and their subunits.
(Hint - activity, all 3 types of radiation in physics, describe the most active and then how the other two connect to the membrane when inactive what all 3 subunits form)
- highly-mobile intracellular membrane proteins with 3 subunits (α, β and γ)
- α subunit:
• more mobile than β and γ subunits
• functions as a GTPase enzyme (converts GTP → GDP) - β and γ subunits – form complex which is v. hydrophobic therefore they stay closely associated w/ the membrane
- when inactivated, all 3 subunits form complex with GDP bound to α-subunit
(see notes for diagram of resting state)
Describe the 3 stages of (G-protein-coupled) activation of type 2 receptors.
(Hint - use the diagrams on your notes)
1)
- ligand + receptor (bind) → conformational change in α, β and γ complex
- α-subunit dissociates from other 2, converts: GDP → GTP
2) α-subunit coupled to GTP, associated with specific allosteric target enzyme (e.g. adenylate cyclase)
3)
- α subunit hydrolyses GTP → GDP
- inactivates enzymatic ability of α-subunit + allows activation of target enzyme
- inactive α-subunit re-associates with β and γ complex
- G-protein changes: substrate → product.
(see notes for diagrams)
What can a G-protein mechanism act as and how?
- signal amplifier
- single activated receptor can activate several G-proteins
Which 4 membrane proteins do targets for G proteins activate?
(Hint - Na+)
1) adenylate cyclase – producing intracellular cAMP
2) guanylate cyclase – producing intracellular cGMP
3) phospholipase C/inositol phosphate system
4) regulators of ion channels
What is cAMP produced from a type 2 (G-protein) receptor, how is it inactivated, what does it specifically target and what are these molecules subsequently used for?
(Hint - 2, PK and DEs)
• cAMP (cyclic 3’,5’-adenosine monophosphate) acts as a secondary messenger → inactivated by hydrolysis into 5’-AMP
• cAMP:
- specifically targets inactive protein kinases → activate (ATP as phosphate source)
- activate PKs to phosphorylate (activate) downstream enzymes
Give an example of a role that cAMP has in cells.
the breakdown of glycogen in β-adrenoceptors
Which involvements does cAMP have in cells other than β-adrenoceptors, how it can be broken down and how can it be inhibited?
(Hint - cardiac, muscle, p, drugs)
- increased activity of voltage-gated Ca2+ channels in the heart
- inactivation of myosin light chain kinase in SM
- cAMP broken down by phosphodiesterase
- inhibited by drugs (i.e. caffeine)
Describe the 5 stages by which receptor guanylate cyclases act as an example of type 2 receptor. Which secondary messenger is involved?
(Hint - EC + ligand, IC domain + GP, gc → cG, cG binds cG-PK, GK + pi → Thr/Ser residues)
1) ligand binds on extracellular domain
2) G-protein activates intracellular domain (guanylyl cyclase)
3) guanylyl cyclase produces: → cGMP
4) cGMP binds to cGMP-dependent protein kinase (G-kinase)
5) G-kinase phosphorylates downstream proteins on threonine/serine residues
- cGMP = secondary messenger
(see notes for diagram)
How does the receptor phospholipase C (or inositol phosphate system) act as an example of a type 2 receptors and which actions are steps associated with?
(Hint - PIP →
- GP and p-lipase
- PIP splits → Dog + Inspo
- both these products act as 2s
- Dog → PKC → targets
- Inspo leading to Ca release)
- based on phospholipid phosphoinositide-4,5-diphosphate (PIP2)
1. G-protein activates target enzyme (phospholipase)
2. phospholipase splits: PIP2 → diacylglycerol (DAG) + inositol-1,4,5-triphosphate (InsP3)
3. InsP3 + DAG act as 2° messengers
4. DAG activates PKC which is serine/threonine kinase, → phosphorylates certain target enzymes
5. InsP3 binds to endoplasmic receptors → open endoplasmic Ca2+ channels → influx of Ca2+ into cytosol needed for certain actions
How do regulators of ion channels act as an example of type 2 receptors? Give a specific example of this in the body.
(Hint - all about GPs and muscu receptors, main NT, K)
- G-proteins directly activate ion channels.
- e.g. interaction of ACh and muscarinic receptors opens K+ channels via G-protein pathway
What is a kinase?
enzyme that catalyses the transfer of phosphate groups
What are the 4 forms of type 3 receptor?
Hint - TYR, LINKED TYR, TYR P, SER/THR
a. Receptor tyrosine kinases - TYR
b. Receptor linked tyrosine kinases – LINKED TYR
c. Receptor tyrosine phosphatases – TYR P
d. Receptor serine/threonine kinases – SER/THREIONINE
State the six stages by which tyrosine kinases work as an example of type 3 receptors and give 2 examples of molecules.
(Hint - ligand EC, change + 2 poly → dimer, tyr K + Pi, auto Pi by tails, SH2 + SH3, genes affected and cells respond
- 2 hormone examples)
1) ligand binds to extracellular binding site
2) conformational change in shape → 2 polypeptides form dimer
3) cytoplasmic tyrosine kinase activated by phosphorylation
4) autophosphorylation → cytoplasmic tail groups can phosphorylate each other (+Pi)
5) activated tyrosine kinases (phosphotyrosines) now binding sites for proteins with SH2 + SH3 domains → act as ligands.
6) proteins/enzymes + transcription factors are activated → gene transcription altered → cellular response
- i.e. receptors for growth factors + insulin
(adapter protein – an important class of protein)
(see notes for image of process)
State the molecule that each abbreviation stands for and state the other names where applicable:
a) GAP (Hint - GTPase…)
b) GEFs (Hint - a type of DNA base exchanger + how to ask for help in WW1)
c) Raf (Hint - ser/thr and k.)
d) ERK (Hint - an EC type of SR kinase)
e) TF
f) FAK (Hint - like adjusting + then sticking on your glasses)
a) GTPase activating protein
b) Guanosine exchange factors i.e. Sos
c) serine/threonine kinase i.e. MAPKKK
d) extracellular signal regulating kinase
e) Transcription factor
f) Focal adhesion kinase
Explain integrins and the integrin protein family as an example of receptor-linked tyrosine kinases type 3 receptors.
(Hint - all about cell parts attaching, 2 types of radiation and di elements)
- integrins → typical example
- proteins which function by attaching cell cytoskeleton + ECM → biochemically sensing whether adhesion occurs
- α + β subtypes which form transmembrane heterodimers (2 different proteins joined)
State the 4 stages of the messenger process of receptor-linked tyrosine kinases an example of type 3 receptors.
(Hint - The 2 GeRBert brothers (Vinculin and Paxilin) ran into trouble when trying to steal a TALoN from Actin and so SeCuRity came after them and they were F’d so they called out for help (SOS). So that is how they got into trouble/the bad situation in the first place)
draw the image to help you
- binding of a ligand (e.g. collagen) to integrins
- allows chain to interact with structural proteins (e.g. talin + vinculin)
- adapter proteins and membrane-bound tyrosine kinases (e.g. Src)
- then phosphorylate another downstream tyrosine kinase FAK
(see notes for image)
What are receptor tyrosine phosphatases and receptor serine/threonine kinases as examples of type 3 receptors and how do they differ from receptor tyrosine kinases?
(Hint - tyr p add water and see/thr add Pis)
- both activated in same way as receptor tyrosine kinases, but:
- receptor tyrosine phosphatases - function to deactivate target proteins by hydrolysis
- receptor serine/threonine kinases - specifically phosphorylate proteins
Which components are required in the signalling process?
Hint - DACT
1) discriminator (receptors)
2) transducers (allosteric enzymes activated/inactivated by substrate binding) i.e. G-proteins, membrane linked tyrosine kinase
3) amplifiers (second messengers - allosteric enzymes activated to different degrees with multiple binding sites)
4) couplers (adapter proteins - allow allosteric enzymes to form close associations, enabled by adapter proteins)
What is Ras, what family does it belong to and what are the other members of this family?
(Hint – all of the Raf brothers Rab, Ras, Rho + Rac are part of the same family)
- a small GTPase
- other members of this GTPase family:
1. Rho and Rac - GTPases → associated w/ integrin to cytoskeletal signaling
2. Rab - family of GTPases → associated w/ intracellular transport
3. Ras
Describe Ras.
(Hint - in the family, Ras is the main man and the others are all sidemen. Ras has a motor like a trimetric G-protein motor but it’s a dead motor as it is 100x slower than one)
- can exist in active (GTP-bound) OR inactive (GDP-bound) states
- functions like trimeric G-proteins but hydrolyses GTP 100x slower
- could mean it stays active for long periods of time
Which 2 regulatory proteins control the GTPase (Ras, Rhab, Rho and Rac) family and how?
(Hint - a jumper brand and the name of a toy giraffe)
1) GAP - acts to enhance Ras hydrolysis rate
2) GEFs (i.e. Sos) - promotes exchange of GDP for GTP
Describe Ras activation of MAP (mitogen-activating protein) kinase using the following keys:
→ = phosphorylation --- = activation ‘’’’’ = promotion of transcription
(Hint – The 2 GeRbert brothers got into a bit of trouble and so one of their mates from the RAb brothers ‘Ras’ came to help them out and he came along really actively (hence the GTP) with his brother [start here] Raf who came in his MEK motor but there was too much trouble and one of them ended up in the EmeRgency room. So the rest of them went looking for this room but the MAPKK was too complex so they simplified it down to MAPK but then the police came and they realised they needed to get TF out so GENE TRANSCRIPTION could occur)
Raf → MEK — serine/threonine kinase ERK → MAPKK → MAPK → TF (transcription of a specific gene)
(see document for diagram)
Usually, what type of receptors are type 4 receptors?
DNA receptors
Describe the structure of type 4 receptors.
Hint - 4-10 in nuclear area, two domains which bind different things
- large proteins of 400-1000 AAs found in nucleus
- have binding domain (steriod hormone substrate binds)
- also have DNA-binding domain (DNA binds)
