Transport

Selective permeability

movement across lipid bilayer is dependent on charge/polarity and size

Highly permeable

small and nonpolar (O2, CO2)

Less permeable

small and polar (water, urea)

Even less permeable

large and polar (glucose)

Highly impermeable

ions even if small

Vesicular transport

for macromolecules/large particles; endocytosis, exocytosis

Passive transport

no energy input required, simple diffusion, facilitated diffusion

Active transport

energy input required, primary active transport, secondary active transport

Osmosis

passive movement of water

Pinocytosis

"cell drinking," ingestion of fluid and solutes, virtually all cells

Phagocytosis

"cell eating," ingestion of large particles (i.e. bacteria, dead cells), used in WBCs

Receptor-mediated vesicular endocytosis

selective uptake of material via endocytosis

Ligand

molecule that binds to receptor and alters its activity

Exocytosis

export material from inside the cell to outside the cell via vesicle fusion

Diffusion

movement of many molecules across membrane

Simple diffusion

movement of freely permeable solutes across the membrane from region of high concentration to low concentration

Facilitated diffusion

movement from high concentration to low concentration with assistance of an integral protein

Stereospecificity

the way that a molecule fits into a protein (orientation)

Limitations of facilitated diffusion

saturation (limited number of available carriers), stereospecificity, competition

Channels

membrane protein that forms a channel to pass through

Non-gated channels (pores)

membrane protein that forms an aqueous passageway that is always open

Gated

passageway that is intermittently open and closed

Carriers

membrane proteins that bind substance at one end, undergo conformational change, and transport substance to other side of membrane

Active transport

movement of solute from low concentration to high concentration, energy required

Primary active transport

ATP is directly coupled to solute movement

Na+/K+ ATPase (Na+/K+ pump)

Plasma membrane of virtually all cells in the body; Transport 3 Na+ out of cell and 2 K+ into cell per 1 molecule of ATP

Ca2+ ATPase (Ca2+ pump)

Plasma membrane of most cells; Pump calcium out of cell; Membrane of sarcoplasmic reticulum; endoplasmic reticulum: pump calcium into SR and ER from cytosol

ATPase

carrier is an enzyme that hydrolyzes ATP to yield ADP +P

Secondary active transport

ATP is indirectly coupled to solute transport

Co-transport (symport)

secondary active transport with solutes moving in the same direction

Counter-transport (antiport)

secondary active transport with solutes moving in opposite directions

Osmosis

passive movement of water through a semi-permeable membrane

Aquaporins

integral membrane pore proteins which allow water to pass

Osmolarity

number of dissolved particles per unit of volume

Colligative property

dependent on total number of particles in a given amount of solution. Not dependent on size, charge

Isosmotic

two solutions have same osmolarity

Hyperosmotic

solution with higher osmolarity

Hyposmotic

solution with lower osmolarity

Hydrostatic pressure

the fluid pressure inside its vessel (i.e. blood pressure); can oppose osmotic pressure; can limit the movement of water

Biological property

the effect of osmotic solutions on the cell

Tonicity

dependent on the concentration of impermeant solute

Isotonic

no osmotic flow, equal concentrations

Hypotonic

lower concentration, causes water flow out

Hypertonic

higher concentration, causes water flow in

0.9% NaCl

Normal saline