secondary messengers

cAMP phosphodiesterase

converts cAMP to AMP to terminate signal

CREB

cAMP response element binding protein
transcription factor which regulates gene expression by binding to cyclic nucleotide response element

secondary messenger

molecules that relay signals from cell surface receptors to target molecules inside the cell or nucleus

nucleotides

monomers of DNA

adenylyl cyclase

converts ATP to cAMP
cleaves off 2 phosphates from ATP and cyclises remaining phosphate from 5 to 3' of sugar

mechanism of PKA activation

2x cAMP bind to each regulatory subunit
allows for release of catalytic dimer in activated form

transcription factor

regulatory protein that binds to DNA and affects transcription of specific genes

how is the soluble form of cGMP activated

by nitric oxide - lipid soluble gas

cyclic nucleotides

cAMP and cGMP

hydrolysis

breakdown of compound by addition of water

kinase

enzyme that catalyses transfer of phosphate group from ATP to specified molecule

targets of cAMP

binds to CN (ligand) gated ion channels
binds to and activates PKA - initiates kinase cascade

PKA structure

4 subunits - 2 catalytic and 2 regulatory

how does cGMP regulate phototransduction ?

in dark cGMP continually produced
ion channels stay open due to Na+ influx - releases neurotransmitters
in light cGMP levels drop, ion channels close and and reduction in neurotransmitters detected by brain

rhodopsin

the pigment in rod cells that causes light sensitivity
activates transducin

transducin

the G-protein that couples rhodopsin to phosphodiesterase in rod photoreceptors which breaks down cGMP

2 configurations of retinal cofactor in rhodopsin

11-cis and all trans

nitric oxide synthase

converts L-arginine and O2 to citrulline and nitric oxide

targets of nitric oxide

pathogens, G cyclase, smooth muscle (relaxes it)

retinol is derived from...

vitamin A

isomer

compounds with same chemical formula but different structures

phospholipase

cleaves fatty acids from phospholipids

phosphatidylinositol

abundant in membrane
hydroxyl-rich side group
extracellular
polar inositol head group

what 2 secondary messengers are produced from phosphotidylinositol ?

inositol triphosphate (PIP3) and DAG

what enzyme is responsible for the cleavage of phospholipids to form secondary messengers ?

phospholipase A or C

PIP3

inositol triphosphate
polar head group
water soluble so acts in cytosol
controls calcium release

DAG

diacylglycerol - hydrophobic
activates PKC by increasing its affinity for calcium ions

calciosome

specialised area of ER high in Ca2+

how many Ca2+ are needed to open calcium channel ?

4

calmodulin

calcium modulated signalling protein - facilitates contraction in smooth muscles

how many binding sites does calmodulin have ?

4 - but each Ca2+ bound to 6O2

apart from DAG what does PKC need to be activated ?

PPS - phosphatidylserine

where is PPS found ?

mem

signal transduction

transmission of molecular signals from extra to intracellular

phosphatase

enzyme - removes phosphate group

what is the role of calcium in inositol phospholipid signal transduction ?

mediates calmodulin activity
aids DAG in activating PKC

kDa

kilodalton
atomic mass unit used to describe molecular weight of large molecules eg. proteins

EF hands

Ca2+ binding motif that consists of E and F helix with binding site in centre

what are the 2 PKC domains ?

regulatory and catalytic

V1

pseudosubstrate site
folded to sit across active site and prevent binding of sub

V3

hinge region

what PKC domains respond to calcium and DAG ?

C1 and 2

role of RACK proteins in PKC activation

translocate PKC to relevant membrane areas

what allows for the prolonged activation of PKC after calcium levels drop ?

downstream target of initial PKC is lipase enzyme that produces more DAG

3 examples of lipid derived secondary messengers

IP3, DAG, ecoisanoids

eicosanoids are derived from...

arachidonic acid

linoleic acid

essential fatty acid
pre-cursor for AA

essential fatty acids

cannot be synthesised by the body

lysophospholipid

phospholipid from which one fatty acid has been removed

3 ecosanoid types

prostaglandins
thromboxane
leukotrienes

role of prostaglandins

inflammation response
stops platelet aggregation

role of thromboxane

promotes blood coagulation (clotting)

role of leukotrienes

inflammatory mediator

leukotriene effects

muscle contraction
pulmonary artery constriction
increase capillary permeability
mucus secretion

in what cells is leukotriene generation triggered

mast (immune)

PGH synthase

converts AA to PGH2

PGH2

precursor for PGs, thromboxane and leukotrienes

what is meant by "PGH synthase is a bifunctional enzyme" ?

catalyses 2 reactions - COX and peroxidase

what is aspirin an example of

secondary metabolism product

how does aspirin act to decrease the symptoms of inflammation?

acts on PGH synthase - acetylates serine amino acid adjacent to active site thus blocking it
prevents PGH from activating PGH2

analgesic

drug that relieves pain

antipyretic

reduces fever

side effects of aspirin

gastric bleeding
hepatic and cerebral damage in children

why does aspirin have negative side effects ?

inhibits both isoforms of PGH
PGH1 is housekeeping enzyme

agonist

molecule that, by binding to a receptor site, stimulates a response

antagonist

block active site

marine fats are high in...

n-3PUFAs

n-3PUFA example

EPA

EPA benefits

in high levels preferentially used by PGH synthase to form 3 series TxA and PGI which decrease likelihood of clot formation and thus cardiovascular disease

2 common asthma treatments

ventolin and bectotide

Salbutamol (Ventolin)

short acting beta-2 andrenergic receptor agonist
causes smooth muscle to relax allowing for bronchial dilation