AP BIO.: 2.6, 2.7, 2.9 - Membrane Transport & Facilitated Diffusion

Easy passage (selective permeability).

Small, non - polar, hydrophobic molecules.

Difficult/ protein assisted passage (selective permeability).

Large, polar, hydrophilic molecules/ ions.

Passive transport.

Transport of molecule down concentration or electrochemical gradient (NO ENERGY).

Diffusion.

Spontaneous process resulting from constant motion of molecules from high to low concentrations (DOWN CG).

T/ F: Molecules diffuse directly across membrane; diff. Rates of diffusion for diff. Molecules.

True.

Osmosis.

Diffusion of water DOWN concentration gradient across selectively permeable membrane.

T/ F: Osmosis can be thought of as diffusion of water from low solute to high solute.

True.

Facilitated diffusion.

Diffusion of molecules through membrane DOWN concentrtaion gradient via specific transport proteins.

T/ F: Facilitated diffusion increases rate of diffusion for small ions, water, & carbs.

True.

Channel proteins.

Provide hydrophilic channels for molecules/ ions to pass through.

Gated channel proteins.

Only allow passage when there's a stimulus.

Aquaporins.

Specific channels for water.

Carrier proteins.

Undergo conformational changes for substances to pass.

GLUT - 2.

Transmembrane carrier protein that enables passive glucose movements across cell membranes,

Active transport.

Transport of molecule AGAINST concentrtaion gradient (REQUIRES ENERGY).

Adenosine Triphosphate (ATP).

Energy source used by cells.

Conformational change (ATP).

ATP can transfer terminal phosphate group to transport protein, changing shape of transport protein to better move a substance.

Pumps.

Maintains membrane potential by moving substances against concentration W/ ENERGY.

Membrane potential.

Unequal concentrations of ions across membrane, creating electrical charge (electrochemical gradient).

Electrogenic Pumps.

Proteins that generate voltage across membranes -> can later be used as energy source for cellular processes.

Sodium Potassium Pump.

Animal cells use ATP to pump 3 NA+ out & 2 K+ in, creating +1 charges to extracellular fluid (more negative inside cell) to regulate concentrations of NA+/ K+.

Proton Pump.

Integral membrane protein that uses sunlight (for photosynthesis) & NADH/ FADH2 (for cellular respiration) to transport H+ across membrane AGAINST concentration gradient.

Proton gradient.

Difference in proton concentration across membrane created by proton pump.

NADH & FADH2.

Electron carriers that donate electrons to ETC.

Cotransport.

Coupling of favorable (down CG) movement of 1 substance w/ unfavorable (against CG) movement of another substance.

How does cotransport power "unfavorable" movement ?

Takes advantage of favorable movement (natural diffusion) to power unfavorable movement -> uses potential energy stored in electrochemical gradients (generated by pumps) & energy created by movement DOWN cg to move other substances against cg.

Sodium Glucose Cotransporter (SGLT).

Needs to have favorable movement of sodium to power movement of glucose.

Uniport.

1 molecule.

Antiport.

2 molecules in opp. Directions.

Symport.

2 molecules in same direction.

Sucrose H+ Cotransporter.

Sucrose moves into plant cell against concentration gradient.

How is sucrose able to move into plant cell against concentration gradient in Sucrose H+ Cotransporter ?

High H+ concentration outside, low H+ concentration inside; low sucrose concentration outside, high sucrose concentration inside -> H+ movement moves down cg = favorable -> powers active transport, allowing sucrose to be pumped against gradient.

Exocytosis.

Secretion of molecules (gen. From RER) via vesicles that fuse to plasma membrane by forming a bilayer.w

What happens once vesicles fuse to membrane during exocytosis ?

Vesicle contents are released to extracellular fluid.

Endocytosis.

Reuptake of molecules from vesicles fused from plasma membrane.

Phagocytosis ("cell eating").

When cell engulfs particle w/ pseudopodia to be packaged into food vacuole & digested by lysosome.

Pinocytosis ("cell drinking").

Non - specific uptake of extracellular fluid containing dissolved molecules in protein - coated vesicle.

T/ F: protein - coated vesicle in pinocytosis helps mediate transport of molecules.

True.

Receptor mediated Endocytosis.

Specific reuptake of molecules when solute binds to receptors (clustered in coated vesicle) on plasma membrane, allowing cell to take up large quantities of specific substance.