Lecture #5 Membrane Transport & Cell Communication

Membrane Transport i.diffusion ii.facilitated diffusion iii.active transport

Diffusion O2O2 CO 2 -molecules pass through membrane -movement is spontaneous -molecules travel down the concentration gradient -goal: equlibrium -speed is limited by rate of diffusion INTRACELLULAR EXTRACELLULAR

Osmosis movement of water down a concentration gradient difference in concentration of solute across a membrane intracellular [solute] vs. extracellular [solute] osmotic, hyperosmotic, hyposmotic

Facilitated Diffusion molecule is transported down its concentration gradient faster and more efficient than diffusion uses transport proteins 2 kinds: carrier proteins channel proteins

GLUT – glucose transporter proteins INTRACELLULAR EXTRACELLULAR GLUT1 – red blood cells, adipose cells, muscle cells glucose insulin GLUT4 – liver cells, adipose cells, muscle cells after glucose uptake

Active Transport pumping a molecule against its concentration gradient requires energy (ATP)

Ca 2+ -ATPase – skeletal muscle CYTOPLASM ER LUMEN Ca 2+ ATP Ca 2+ P

Na+-K+-ATPase – nerve stimulation and membrane potential INTRACELLULAR K 2+ Na 2+ ATPADP EXTRACELLULAR K 2+ Na 2+ restingstimulated Na 2+ K 2+ Na 2+ K 2+ stimulation release of energy

Active Transport and Co-transport bloodgut epithelial cellintestinal lumen tight junctions K 2+ Na 2+ ATPADP K 2+ Na 2+ glucose

Other forms of transport Exocytosis Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis

Cell Signalling Signals: local regulators – e.g. growth factors long-distance regulators – e.g. hormones 3 stages: Reception Transduction Response

Non-hormonal cell-to-cell communication

Reception – Plasma Membrane Receptors 3 major types: G-protein linked receptors receptor tyrosine kinases ion channel receptors

G-protein linked receptors ligands: e.g. some hormones (epinephrine) neurotransmitters

Epinephrine – adrenergic receptor epinephrine – produced by the adrenal gland enters the bloodstream during short-term stress response liver -  1 receptors blood vessels -  2 receptors

Liverblood vessels - heart, lung, cerebral cortex  1 receptor adenylate cyclase GTP  1 receptor adenylate cyclase GTP ATP cAMP PKA glycogen breakdown – release glucose  2 receptor adenylate cyclase GTP  2 receptor adenylate cyclase GTP ATP cAMP PKA inhibits MLCK – vasodilation

blood vessels – skin and gut  2 receptor adenylate cyclase GDP  2 receptor adenylate cyclase GDP ATP cAMP X vasoconstriction

Receptor Tyrosine Kinases kinase: an enzyme that phosphorylates another protein – catalyzes the transfer of phosphate groups RTKs – catalyze the transfer of phosphate to side chain of tyrosine amino acid in a protein ligands – e.g. growth factors – EGF, FGF, PDGF, etc.

Transduction protein phosphorylation – kinases second messengers: cAMP Ca 2+

Transduction phosphorylation - kinases – growth factors »stimulate cell division cAMP – adenylate cyclase »activates PKA »various effects – e.g. glycogen breakdown or vasodilation Ca 2+ - PLC produces IP 3 and DAG »activates PKC »various effects – e.g. muscle contraction

Response Cytoplasmic responses: –opening or closing of a gated ion-channel –alteration in metabolism –regulation of enzyme activity –change in cytoskeletal organization Nuclear responses –activation or repression of gene expression »activation or inhibition of cell cycle »induction of differentiation »cell committment