M & R Flashcards
Chemical signals may be classified according to their functions into
hormones
neurotransmitters
localchemicalmediators
Types of Signaling
Autocrine
Chemicals relaeased by the cells stimulates the crll itself
Paracrine chemicals released by the cell stmulate the neighboring cell
Endocrine
Juxtacrine direct contact or interaction between the cells via complementary surface proteins
Juxtacrine signaling like
Gap junctions and interaction between the complementary proteins if the t cell and APC
Agonist
Antagonist
Partial agonist
Is a ligand that binds to the receptor and activates it
Is a lingand that binds to the receptor without activating it
Partial agonist it activates the receptor but cant elicit the maximum response
Receptor
Binds to a specific ligand to regulate cellular a process
For a cell to respond to any chemical messenger it must produce
specific receptor that recognizes and produces a response to the signaling molecule
Properties of receptor binding sites
binding is specific.
Shape of the binding site determines specificity
Binding is most ofen reversible
ligand/receptor binding induce a conformational change and a change in the activity of the molecule.
no chemical modification occurs (ligand bound to a
receptor site is not modified chemically
Receptors are two types
Cell surface receptor (mostly transmambrane )
Intra cellular receptor (in neucleas or cytoplasm
Cell surface receptors
Ion channel linked receptor(ligand gated ion channel )
When it binds to the receptor it undergoes a conformational change opening the ion channel and let the ions to pass through
Where do you find them
Nicotinic ACH receptor
GABA receptor
Glycine receptor
Receptors of the ligand gated ion channels
They have a similar pentametic subunit structure each subunit with four transmembrane domains the m2 lines the pore of the channel
Enzyme-linked receptors
Their cytosolic part has intrinsic enzymatic activity or associated with an enzyme
Enzyme linked receptor types of enzymes
Tyrosine kinase linked receptor
Guanylyl cyclase linked receptor
tyrosine kinase-linked receptors
Growth factor receptor
PDGR
EGF
Insulin
guanylyl cyclase-linked receptors.
ANP receptor
coupled to guanylyl cyclase
Binding a hormone(ligand) to the receptor causes
Two receptor linked tyrosine kinase dimerize and activating the kinase enzyme on the cytoplasmic domain autophosphorylating tyrosine residues
Phosphorylated tyrosine residues is recognised by
transducing proteins e.g. insulin receptor substrate-1 (IRS-1)
Or
enzymes containing phosphotyrosine recognition sites, Src-homology-2 (SH2) domains.
G protein coupled receptor (no enzyme no ion channel)
It spans the membrane 7 times
Binding to a ligand causes a conformational change that exchanges GDP to GTP on the G protein then the G protein subunits dissociates into betagamma dimer and GTP bound alpha subunit which they transfuce the channels or enzymes
Intracellular receptors during resting dtate stabilised by
Heat shock proteins or chaperene proteins
ACCEPTORS
The molecules that their basic function carried out without interaction with a ligand
Many molecules their activities are modified by binding to small molecules
They are not strictly receptors
