Chapter 5: Membrane Dynamics

plasma membrane

composed of a phospholipids bilayer, hydrophilic phosphate heads and a hydrophobic tail, cholesterol molecules that help stabilize the cell membrane (tooth pick)

receptor proteins

receive and transmit messages into the cell

integral proteins

form specialized doorways for specific molecules

cellular adhesion molecules (CAMs)

(desmosomes or gap junctions) that allow the cells to stick to each other and allow small molecules to move between the cytoplasm of adjacent cells

tight junctions

the cell-cell junctions act as barriers to minimize the unregulated diffusion of material between cells, so there is very little paracellular transport

(cells that line the small intestine)

carbohydrate chain

antigen (cell marker) identify self to self

passive transportation (not requiring energy) through the cell membrane

osmosis

filtration

facilitated diffusion

diffusion

osmosis

diffusion of water using kinetic energy (H2O follows solute)

filtration

moves from high to lower concentration (moving out of an airport)

uses hydrostatic pressure

facilitated diffusion

moves from higher to lower concentration with the aid of a transporter faster movement using kinetic energy

tonicity

describes a solution and how that solution affects cell volume (H2O follows solute)

hypotonic

cell swells when placed in solution and therefor gains water

hypertonic

cell shrinks when placed in solution and therefore loses water

isotonic

cell neither gains or loses water when placed in solution

diffusion

moves substances from higher concentration to an area of lower concentration

fick’s law of simple diffusion

how it moves out of membrane

channel protein diffusion

utilize membrane-spanning protein subunits with a tunnel or pore which is open at both ends at the same time

carrier protein diffusion

utilize membrane-spanning protein subunits that bind to the substrates that they carry, but never form a direct connection between the intracellular and extracellular fluids

(revolving door)

bulk transport through the cell membrane (requires energy and ATP)

active transport (direct/indirect)

endocytosis

exocytosis

active transport

moving substances against the concentration gradient, selectively permeable

sodium - outside

potassium - inside

low to high concentration

primary (direct) active transport

the energy to push molecules against the concentration gradient comes directly from the high-energy phosphate bond of ATP

secondary (indirect) active transport

uses the kinetic energy in one molecule moving down its concentration gradient to push other molecules against their concentration gradient

endocytosis

into the cell - an indentation by the membrane, surround and pinched off and moved to where it will be digested in a much smaller vesicle

pinocytosis, phagocytosis, receptor mediated

phagocytosis

cell eating (going after it) using a large membrane-bound vesicle

pinocytosis

cell drinking

receptor mediated endocytosis

active mediated transport

exocytosis

out of the cell - enclosed by the membrane in a vesicle and transported out of the cell thus rupturing outside the cell (secretion)

specificity

the ability of a carrier to move only one molecule or only a group of closely related molecules

competition

where a transporter may move several members of a related group of substrates, but those substrates will compete with one another for the binding sites on the transporter

saturation

depends on both the substrate concentration and the number of carrier molecules

paracellular transport

movement occurs through the junctions between adjacent cells

(plasma, interstitial fluid of GI tract)

transcellular transport

movement occurs through the epithelial cells themselves forcing the crossing of two cell membranes

(alveoli and blood)

gap junctions

allow small molecules and ions to move between the cytoplasm of adjacent cells

(muscle cells of the heart and digestive tract)

desmosomes

attach the intermediate filaments of the cytoskeleton. strongest of the cell-cell anchoring junctions

(muscles of the heart)

secretion or ejection of substances from a cell

the substance is enclosed in a membranous vesicle which fuses with the plasma membrane and ruptures. releasing the substance to the exterior

mass balance

existing body load + [intake/metabolic production] - [excretion/metabolic removal]

clearance

rate at which molecule disappears from the body

mass flow = concentration x volume flow