bio 141 ch 5: cell membranes

fluid mosaic model

mosaic of proteins floats in or on the fluid lipid bilayer like boats on a pond

phospholipid structure

glycerol, two fatty acids, phosphate group

glycerol

3 carbon polyalcohol

two fatty acids

attach to glycerol in phospholipids. nonpolar and hydrophobic

phosphate group

attach to glycerol in phospholipids. charged and hydrophilic

four components of cellular membranes

phospholipid bilayer, transmembrane proteins, peripheral protein network, cell surface markers

cell surface markers

glycoproteins or glycolipids

saturated fatty acids in a bilayer

can withstand warmer temperatures, less fluid

unsaturated fatty acids in a bilayer

colder temperatures, more fluid

transmembrane domain

hydrophobic amino acids arranged within fatty acid region

pores

polar interior allows water and small polar molecules to pass through the membrane down their concentration gradient

diffusion

movement of molecules from high concentration to low concentration

passive transport

movement of molecules through a membrane in which no energy is required and molecules move in response to a concentration gradient

selectively permeable

membranes are…

small nonpolar molecules

can pass through the membrane easily

small uncharged polar molecules

some will bounce off, others can pass through the membrane

large uncharged polar molecules

most will not pass through the membrane

ions

cannot pass through selectively permeable membrane

facilitated diffusion

molecules that cannot cross membranes easily may move through proteins from higher to lower concentration

channel proteins

hydrophilic when open; pore with a door

carrier proteins

bind to molecules and change shape

channel proteins

allow the passage of ions, highly polar substances, and bulky molecules through nonpolar interior of plasma membrane

channel proteins

facilitated diffusion only

carrier proteins

must bind to the molecule they transport

osmosis

net diffusion of water across a membrane toward a higher solute concentration

hypertonic

higher solute concentration in environment

hypotonic

lower solute concentration in environment

isotonic

two solutions have the same solute concentration

hypotonic

human red blood cells will swell and eventually burst

turgid

swollen

isomotic regulation

involves keeping cells isotonic with their environment

osmotic pressure

used by plant cells to push the cell membrane against the cell wall and keep the cell rigid

turgor pressure

the force within the cell that pushes the cell membrane against the cell wall

active transport

requires energy; ATP used directly or indirectly; moves substances from low to high; requires the use of highly selective carrier proteins

uniporter

carrier protein that moves one molecule at a time

symporter

carrier protein that moves two molecules in the same direction

antiporter

carrier protein that moves two or more molecules in opposite directions

coupled transport

combined action of antiporter and symporter

Na+/K+ pump

direct use of energy from ATP for active transport; uses an antiporter to move 3 Na+ out of the cell and 2 K+ into the cell against both concentration gradients

affinity

changes for either Na+ or K+ so ions can be carried across the membrane via the carrier protein

symporter

uses ATP indirectly

glucose/Na+ symporter

captures energy from Na+ diffusion to move glucose against concentration gradient

endocytosis

bulk transport of substances into the cell; requires energy

exocytosis

bulk transport of substances out of the cell; requires energy

exocytosis

used in animals to secrete hormones, neurotransmitters, digestive enzymes