Cell Transport Flashcards
Diffusion
mvmt along concentration gradient (high to low); no ATP required
Simple diffusion
- direct passage through membrane
- kinetic mvmt of molecules/ions provides motion
- high to low conc
- in cells, diffusion occurs directly through the cell membrane or through protein pores in the cell membrane (channel protein)
Faciliated diffusion
utilizes membrane protein for import/export
Active Transport
requires energy (hence active) typically moving against conc gradient 2 types: primary and secondary active transport
Endo and exocytosis
specialized transport mechanisms
Membrane Transport-General
- Lipid soluble molecules pass directly through phospholipid bilayer: O2, CO2, alcohol
- Some H2O soluble molecules pass through the cell membrane using channel protein pores: H2O, PRO, some ions, lipids bound to PRO
- Many substances are transported against their conc. gradient (active transport)
General Permeability rules
Small HydroPHOBIC molecules: (O2, CO2, N2, benzene) simple diffusion
Small uncharged POLAR molecules:( H20, glycerol, ethanol) simple diffusion
Larger uncharged POLAR molecules: (AA, Glucose, nucleotides) facilitated
Ions: (H+,Na+, HCO-3, K+,Ca2+,CL-,Mg2+) facilitated
Intracellular//Extracellular composition
Na+= 140mEq/L (E)/ 10 mEq/L (I) K+= 4mEq/L (E)/ 140 mEq/L (I) Cl-= 103mEq/L (E)/ 4 mEq/L (I) Glucose= 90mg/dL (E)/ 0-20mg/dL (I) Proteins= 2g/dL (E)/16 g/dL (I)
Factors affecting simple diffusion
- amount of substance available
- lipid solubility of diffusing substance
- # and size of membrane openings (channels)
- velocity of kinetic motion of molecules (greater temp=faster difusion)
- molecular weight-smaller particles move more rapidly
- distance-shorter distance=faster diffusion
Facilitated Diffusion “carrier mediated diffusion”
- requires interaction of carrier protein
- carrier protein binds the transported molecule (ion) and shuttles the molecule through membrane w/o energy source
- conformational change in carrier protein causes molecule to move through membrane
- molecule must be moving along its conc gradient
Factors affecting facilitated diffusion
- rate is regulated by ability of carrier protein to complete the transport
- once carrier proteins are “saturated” no increase in diffusion rate is possible
- molecules can move in either direction using the same carrier protein-(depending on conc gradient)
Simple vs. Facilitated
Facilitated: limited by number of available transport PROs in membrane
Simple: occurs at all parts of the membrane
-limited only by conc. gradients
Osmosis
net mvmt of water along its conc. gradient
–requires a semi-permeable membrane separating fluid compartments
Osmotic pressure
driving force for osmosis across a membrane
- -directly related to the solute conc. of the two fluid compartments
- -water tends to move from low to high
Hydrostatic pressure
fluid pressure
- -force that water transmits via its weight (i.e. water tower) or via its flow through a vessel (blood flow)
- -tends to equalize with the osmotic pressure to prevent too much loss/gain of water from cells & tissues
Active transport
transport of substances across the cell membrane which requires energy expenditure
- –molecule move against the conc. gradient
- Ions (Na, K, Ca, Cl, H)
- Large molecules (glucose, PRO)
both types utilize carrier proteins
Primary active transport
direct utilization of ATP as energy source
Secondary active transport
energy for transport comes from stored energy of ionic conc. gradient b/w intracellular and extracellular environments
—ionic conc. gradient is initially created by primary active transport of the ion of interest
Na+/K+ pump: active transport
- Membrane protein actively pumps 3Na+ ions OUT of cell and 2K+ ions INTO cell using ATP
- responsible for setting up ionic conc. gradients b/w intra and extra cellular spaces
- important for maintaining a voltage across the cell membrane (- inside, + outside)
Co-transport
method of transport for glucose and AAs
- -AAs are transported into cell against conc. gradient; sugars move w/ conc. gradient
- -transport occurs in conjxn w/ Na athat move down their CG and into cell
- -Carrier PRO is specific for sugars and AAs
- -both the transported molecule and Na+ must be bound to the carrier protein for transport to occur
Counter transport
Transport of molecules in opposite directions across the cell membrane; uses energy of conc. gradient of one of the transported molecules
- –example: Ca+ moving out of cell using Na+ moving into cell
- –maintains overall ionic balance of intra and extra cellular space
Endocytosis
Passage of material into a cell moving through cell membrane; requires energy use by cell
Phagocytosis: endocytosis
uptake of particulate material; only “recognized” particles are engulfed
Pinocytosis: endocytosis
uptake of soluble molecules (water); non-specific engulfment of molecules
Receptor mediated endocytosis
- -uptake of specific molecules using specific membrane proteins (clathrin)
- -ingested particle first binds to clathrin
- -binding to clathrin activates invaginations of cell membrane, bringing particle into cell
- -vesicle brought in disassembled by cell; ingested material retrieved and protein receptor is recycled back to cell membrane
Exocytosis
Process of secreting/releasing most proteins made by cells
vesicles from Golgi app move toward cell membrane and fuse with it
as fused membranes flatten out the vesicle contents are released into the interstitial space
