ch5 bio

general stucture of membranes is known as

like a "lake" in which is variety of proteins "float"

maintain a bilayer organization spontaneously helps membranes fuse during phagocytosis, vesicale formation, etc

phospholipids vary fatty acid chain length, degree of saturation, phosphate groups

membranes contain proteins, the number of proteins varies with cell function

the proteins and lipids in the membrane are independent and only interact noncovalently

spand the bilayer, hydrophilic ends protrude on either side

dont penetrate teh bilayer

may have different domains on either side of the membrane

the two sides of the membrane can have very different properties

some membrane proteins can be anchored by cytoskeleton elements or lipid rafts lipids in semiolid state

membranes are dynamic and are constantly forming and transforming and fusing and breaking down

membranes have cabs on the outer surface that serve as recognition sites for other cells and moelcules

cells arrange themselves in groups by cell recognition and cell adhesion

binding of cells is usually homotypic: the same molecule sticks out from both cells and forms a bond

help ensure directional movement of materials

like spot welds

allow communication

some substances can pass through but not others in membranes

no outside energy required- diffusion

energy is required for passing through

teh process of random movement toward equilibrium

particles continue to move, but there is no net change in distribution

new movement is directional until equilibrium is reached

diffusion trate depends on diameter of the moelcuesl or ion, temperature of the solution, electric charges, concentration gradient

membrane properties affect the diffusion of solutes

small moelcules pass through the lipid bilayer

lipid soluble moecules can diffuse across the membrane as can water

the diffusion of water

osmosis depends on the number of solute particles present no tthe type of particlesif 2 solutions are separated by a membrane that allows watherbut not solutes to pass throughwather will diffuse from the region of higher wather concentration (lower solute concentration) to the region of lower water concentration (higher solute concentration)

equal solute concentration( and equal water concentraion)

higher solute concentraion

lower solute concentration

water will diffuse (net movement) from a hypotonic solution across a membrane to a hypertonic solution

plant cells with rigid cell walls build up internal pressure that keeps more water from entering (TURGOR PRESSURE)

polar molecules can cross the membrane through channel proteins and carrier proteins

have a central pore lined with polar amino acids

important channels proteins, most are gated can be closed or open to ion passage, gate opens when protein is stimulated to change its shape. stimulus can be a molecule or electrical charge resulting from many ions

gradients can be a concentration gradient of ions, or an electrochemical gradient resulting from a charge imbalance across the membrane

water may pass through the membrane by hydrating ions that pass through a channel

transport polar molecules such as glucose across membranes

glucose binds to the protein which causes it to change shape

moves substances against a concentration gradient requires energy

active transport involves 3 kinds of proteins:
uniports, symports, and antiports

requires direct participation of atp

energy comes from an ion concentration gradient that is established by primary active transport

primary active transport, found in all animal cells, the pump is an tegral membrane glycoprotein. it is an antiport

energy can be "regained" by letting ions move across a membrane with the concentration gradient- secondary active transport, aids in uptake of amino acids and sugars, uses symports and antiports

processes that bring molecules and cells into a eukaryotic cell ( the plasma membrane folds in or invaginates around teh material, forming a vesicle)

molecules or entire cells are engulfed. some protists feed in this way. some whte blood cells engulf foreign substances. a food vacuole or a phagosome forms which fuses w a lysosome

a vesicle forms to bring small dissolved substances or fluids into a cell. vesicles are much smaller than in phagocytosis. constant in endothelial cells

highly specific, depends on receptor proteins integral membrane proteins - to bind to specific substances, sites are called coated pits- coated with other proteins such as clathrin

mammalian cells take in cholesterol by receptor- mediated endocytosis

liver must take up low-density lipoproteins for recycling. teh ldls bind to specific receptor proteins

material in vesicles is expelled from a cell. indigestible materials are expelled. other materials leave cells such as digestive enzymes and neurotransmitters

(keeping different materials separated)
endoplasmic reticulum segregates newly-formed proteins

membranes help transform energy:
-inner mitochondrial membranes- energy from fuel molecules is transformed to atp
-thylakoid membranes of chloroplasts transform light energy to chemical bonds

many cellular processes involve a series of enzyme-catalyzed reactions- all the moelcules must come together for these to occur. forms an assembly line of enzymes

the cholera toxin - one subunit binds to a cell surface receptor- the toxin molecule changes shape and allows the other subunit to enter teh cell
-the subunit acts as an enzyme to modify a peripheral protein- this opens chloride channels in the membrane
- cl- and na+accumulate in teh intestines, followed by osmotic loss of water