Session 6.1 Biological Signalling - Receptors and Ligands Flashcards
how can intercellular signalling occur
signalling cell secretes a signalling molecule which attaches to receptor in target cell and causes a change
signalling by plasma membrane bound molecules which then attach to a receptor in target cell
what are the different types of signalling by secreted molecules
paracrine
endocrine
synaptic
what is paracrine signalling
signalling molecules secreted from cell into interstitial space within tissue, recognised and causes response in tissue (local mediator)
what is endocrine signalling
signalling molecule released from signalling cell into blood which circulates in body to target cells in distal tissues
what is synaptic signalling
arrival of action potential at pre-synaptic membrane releases transmitter into synapse which is recognise by receptors in target cell to cause response
what are the subdivisions of signalling molecules
local chemical mediators
hormones
neurotransmitters
can overlap though
where are receptors found
hydrophilic - hormones in blood, no access to inside cell so cell surface receptor
hydrophobic - carrier proteins in blood, released at target tissue, diffuse directly through bilayer into cell, and bind to intracellular receptors in nucleus or cytoplasm
what is a receptor
a molecule that recognises specifically a second molecule (ligand) or family of molecules and which in response to ligand binding brings about regulation of a cellular process
when unbound state = receptor functionally silent
what is a ligand
any molecule that binds specifically to a receptor site
what is an agonist ligand
when bound, produces activation of receptor from silent form
what is an antagonist ligand
when bound, do not cause activation in receptor site, remains silent as preventing binding of agonist
what are the role of receptors in cellular physiology
signalling neurotransmission cellular delivery control of gene expression cell adhesion modulation of the immune response - recognision of foreign bodies sorting of intracellular proteins release of intracellular calcium stores
how tightly does a ligand bind to receptor site
higher affinity than allosteric binding
as ligand is diluted as released from signalling tissue - low concentration
how are receptors classified
classified - specific agonist recognised
sub classification - affinity of antagonists
how are acetylcholine receptors classified
nicotinic - agonist is nicotine
muscarinic - agonist is muscarine
how are muscarinic receptors subdivided
they all can be inhibited by the antagonists but with different potencies at different receptor sites so
M1 = pirenzipine as antagonist
M2 = gallamine
M3 = hexahydrosiladiphenol
what is an acceptor
operate in absence of ligand
if not, ligand binding produces no response
does not need a modulator as not silent at rest, eg: sodium channels with anaesthetic agents, operate normally without
how has evolution solved the problem of transducing extracellular into intracellular signals
- attach enzyme to receptor so when hydrophilic signal attaches, causes conformational change in receptor and release of second messenger (as converted)
- receptor in membrane. ion binds and causes opening of channel
- receptor coupled to effector on separate molecules so binding of agonist causes conformational change which is transmitter to effector which produces second messenger
- separating effectors and receptors by transducing molecules in between, which transduce conformational change onto effector to produce second messenger
- hydrophobic signal enters directly into cell and bind to intracellular cell surface receptor. receptors bind to DNA to control gene expression (activation of transcription factors)
why is coupling receptor and effector a good idea
if effector mutated, other effectors can be activated by receptor…so not so susceptible to mutation
