Lecture 8 - cell communication Flashcards
Local signalling
Acts on nearby target cells; can act on signalling cell
Long distance
Hormones travel through circulatory system to act on far away target cells (insulin)
3 main steps of signalling
Reception, Transduction; Response
Reception
involves receptor protein and signalling molecule binding so receptor changes shape or chemical state
Transduction
Altered receptor protein activates another protein which can cause a cascade of changes often via phosphorylation
Second messengers
Relay molecules (e.g. cAMP IP3, Ca2+)
Response
When cell actually does something, activated proteins will cause at least one function to occur in the cell
Membrane bound vs non membrane bound receptors
Receptors of water soluble molecules are membrane bound (hydrophilic); receptors of lipid soluble molecules are not membrane bound (hydrophobic) and in cytoplasm or nucleus
Examples of membrane bound receptors
Ligand gated ion channels, G protein coupled receptor, tyrosine kinase receptor
Examples of lipid soluble hormones
Testosterone, progesterone, estrogen, thryoid hormones
Which body system relies heavily on ligand gated ion channels?
Nervous system - neurotransmitters bind to ligand gated ion channels on target cells which propagate action potentials
Protein kinases
Enzymes which activate relay molecules by transferring a phosphate group from ATP to the protein (phosphorylation)
Phosphatases
Deactivate (but recyclable) relay molecules by removing phosphate from the protein
cAMP signal pathway
GCPR activates adenylyl cyclase –> cAMP is converted from ATP by adenylyl cyclase –> activates downstream proteins as second messenger
Ca2+ as second messenger requirements
Needs to be pumped out of cell or into ER or into mitochondria to maintain low conc Ca2+ in cell and high conc outside of cell
Ca2+ and IP3 signal pathway
G protein coupled receptor activates phospholipase C –> cleaves PIP2 into IP3 and DAG –> IP3 binds to gated channel of ER –> Ca2+ diffuses into cytosol activating other proteins –> cellular response
benefits of phosphorylation cascade (multi steps)
Amplification, control points, specificity (temporal, spatial) of response despite common molecules, coordinate with other signalling pathways
Phosphodiesterase (PDE)
breaks down cAMP to deactivate response
Adrenalin pathway
Ephinephrine binds to GPCR –> adenylyl cyclase –> ATP to cAMP –> two protein kinases –.> lots og glycogen to glucose 1-phosphate. Each step mega amplification
Glycogen to ATP
Glycogen -> glucose 1-phosphate -> glucose 6-phosphate
Specificity of receptors
3D shape means structure determines function, only target cells interact with ligand
Types of local signalling molecules
Growth factors: Fibroblast Growth Factor (FGF) paracrine
Neurotransmitters: acetylcholine (synaptic)
