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Transcript
Membrane Structure & Function Membrane Models 1935-1970 Sandwich Model 1972- Present Fluid-Mosaic Model Membrane Transport (Passive) 1 2 Glucose, amino acids Diffusion • Steepness of concentration gradient • Temperature • Mass of diffusing substance • Surface area • Diffusion distance 2 types of membrane transport Passive vs Active Channel-mediated Facilitated Diffusion of Potassium ions through a Gated K + Channel Extracellular fluid Glucose 1 Plasma membrane Glucose transporter Glucose gradient 2 3 Glucose Cytosol http://trc.ucdavis.edu/biosci10v/bis10v/media/ch04/tonicity.html Crenation Hemolysis Cytolysis Turgor pressure – the force directed against the cell wall after the influx of water (osmosis) Plasmolysis – the shriveling of the cell membrane due to loss of water (osmosis) Filtration is movement of water and solute molecules across the cell membrane due to hydrostatic pressure generated by the cardiovascular system. Requires Energy: ex.: thyroid gland concentrates Iodine glucose is completely absorbed by digestive tract sodium potassium pump Active Transport I. Solutes are transported across plasma membranes with the use of energy, from an area of lower concentration to an area of higher Concentration *Sodium-potassium pump *Thyroid gland *Intestines (glucose) II. 2 sources of energy 1. ATP (Primary active transport) 2. Energy stored in Ion concentration gradients (Secondary active transport) **40% of a cell’s ATP is used for Primary active transport Cyanide shuts down active tranport by turning off ATP production Extracellular fluid Na+ gradient Cytosol K+ gradient Cytosol K+ gradient 3 Na+ Na+/K+ ATPase 3 Na+ expelled 2K+ 1 P 3 Na+ 1 ATP 2 ADP 3 P + 4 2K imported Secondary Active Transport Mechanisms • Antiporters carry two substances across the membrane in opposite directions (Digitalis) • Symporters carry two substances across the membrane in the same direction 18 Endocytosis – taking in large amounts of material (bulk flow) • Ex. LDL cholesterol (bad cholesterol)