Chemical Signaling

receptors

proteins with binding sites for specific signalling chemicals

enzymes vs receptors

quorum sensing in bacteria

• a change in behavior of a colony when its population density reaches a certain threshold

• bioluminescence in fibrio fischeri and mutualism with the bobtail squid

hormones

• produced by endocrine gland and transported by bloodstream

• hormones can persist in body for much longer than with nerve impulse

• estrogen, insulin, glucagon, testosterone

neurotransmitters

• transmits signals across synapses

• very quick and rapid removal

• acetylcholine, dopamine, serotonin

cytokines

• proteins that acts as chemical messages within cells or between nearby cells

• multiple effects depending on binding site

calcium ion

muscle fibre - calcium ions bind to a protein on actin to allow myosin heads to attach

neurons - causes the release of neurotransmitters from presynaptic neuron

chemical diversity of hormones and neurotransmitters

localized and distant effects of signalling molecules

• hormones can have effects over large distances

• neurotransmitters produce a localized effect between neurons

Transmembrane receptor in plasma membrane and intracellular receptor in cytoplasm and nuecleus

Initiation of signal transduction pathways by receptor

• transduction pathway - sequence of interactions initiated by the ligands binding to the receptor

• intracellular pathway - ligand enter the cell, binds to receptor, complex regulates gene expression

• transmembrane pathway - ligand binds w receptor, receptor chagnes shape, produces secondary messenger molecules and causes changes within cells

transmembrane receptors for neurotransmitters and changes to membrane potential

• neurotransmitters released from presynaptic neuron

• bind to receptors on post synaptic neuron

• causes sodium ion channels to open

• sodium enters the cell via facilitated diffusion

• changes the membrane potential

• e.g. acetylcholine is a messenger between neurons and muscle fibres

Transmembrane receptors that activate G protein

Mechanism of action of epinephrine receptors

transmembrane receptors with tyrosine kinase activity

Intracellular receptors that affect gene expression

effect of hormones oestradiol and progesterone on target cells

regulation of cell signalling pathways by positive and negative feedback