lecture 15+16 Flashcards
what is non-mediated transport important for
nutrient absorption, excretion of wastes
e.g. non polar, hydrophobic O2, CO2, N, fatty acids, steroids, fat soluble vitamins (ADEK), small alcohol, ammonia
how structure of channel protein allows specificty
specific amino acids line the channel pore
examples of channel stimuli
voltage, ligand, pH, phosphorylation, cell volume(stretch)
facilitated diffusion of glucose
glucose binds to GLUT –> in cell is converted by kinase into glucose-6-phosphate to maintain conc. gradient
primary vs secondary active transport
primary: direct energy from ATP
secondary: indirect energy from another ion conc. gradient
primary active transport examples
Na+/K+, Ca2+/K+(muscle SR), H+/K+ (stomach)
All ATPase
secondary active transport examples
Na+ anitporter/exchanger for Ca2+ or H+ out of cell
Na+ symporter/cotransporter for glucose or amino acids into cell
plasma membrane andp phospholipid structure
8nm (10^-9m), 50% lipid, 50% protein
75% lipid tail, 25% phosphate head
3 types of lipid molecules
cholesterol, phospholipids, glycolipids (generally in ECM lipid layer)
asymmetry of membrane cause
lipids rarely flip flop into different leaflets so the two lipid layers can have different composition
membrane fluidity factors
lipid tail length: longer = less fluid
number of double bonds: more = more fluid as more kinks
cholesterol: more cholesterol = less fluid (actually depends on temp)
nonpolar uncharged molecules permeability + examples
permeable
O2, N2, benzene
lipid soluble permeability + examples
permeable
steroids, fatty acids, some vitamins
small uncharged polar permeability + examples
water, urea, glycerol, CO2
large uncharged polar permeability + examples
impermeable
glucose, amino acids
ions permeability + examples
impermeable
Na+, K+, Cl-, Ca2+, H+
physical consequences of diffusion on cell
limited to 20um, thin pm, need to increase SA
how membrane maintains gradient (conc., electrochemical)
mimics capacitor by separating and storing charge
uses 30% resting energy
Pf features
-mediated by 9 isoforms of aquaporins
-mercury sensitive
-large
-temp independent
Pd features
-direct through pm
-small
-mercury insensitive
-temp dependent
hyposmotic vs hyperosmotic
hyposmotic - less solute, less pressure
hyperosmotic - more solute, more pressure
water moves to high pressure to even out
passive diffusion
no ATP required, solute moves down concentration or electrochemical gradient
