Chapter 8- Biological Membranes Flashcards
cell (plasma) membrane description
semipermeable phospholipid bilayer. made up mainly of lipids w/ some proteins and carbohydrates (few free fatty acids)
-allows fat-soluble compounds to cross easily (through simple diffusion), but not large or water-soluble compounds
glycoprotein coat
created by carbohydrates associated with membrane-bound proteins. cell wall also has high carbohydrate concentration.
phospholipids and membrane dynamics
phospholipids move rapidly in the plane of the membrane through simple diffusion.
Lipid rafts
collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules, typically serve role in signaling. travel though bilayer slowly
flippases
assist in transition or “flip” between layers–> movement of phospholipids b/w layers of plasma membrane b/c it is otherwise energetically unfavorable.
fluidity of membrane
steroid and cholesterol molecules
stability of membrane
waxes
unsaturated fatty acids
come mainly from diet. transported from intestine to chylomicrons. increase membrane fluidity.
glycerophospholipid
triacylglycerol with one of its fatty acid chains substituted for a phosphate (polar head group). phospholipids spontaneously form micelles or liposomes due to hydrophobic interactions.
sphingolipids
do not contain glycerol. contain hydrophilic region and 2 hydrophobic fatty acids. main difference between them are the different hydrophilic regions (ex: ceramide, sphingomyelins, cerebrosides, and gangliosides)
cholesterol in membrane
20% of its mass. 50% mole fraction of membrane. adds fluidity to membrane. stabilizes adjacent phospholipds.
waxes
type of lipid. extremely hydrophobic and rarely found in cell membranes of animals (sometimes found in cell membranes of plant). composed of long fatty acid chain and long alcohol chain (high melting point). in membrane provide stability and rigidity in nonpolar tail region only.
3 main membrane proteins
- transmembrane proteins- pass completely through the lipid bilayer (ex: channels and receptors)
- embedded proteins- associated with only interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane (ex: catalytic activity with enzymes)
- membrane-associated (peripheral) proteins- bound through electrostatic interactions with lipid bilayer, especially at lipid rafts. or are bound to other transmembrane or embedded proteins, like G proteins found in G protein-coupled receptors. (ex: signaling and recognition)
* Note: 1 + 2 are considered integral proteins,
carbohydrates and membrane
generally attached to protein molecules on the extracellular surface of cells. hydrophilic. can act as signaling/recognition molecules. (ex: ABO blood types only differ with respect to carbohydrates on cell)
cell adhesion molecules (CAMs)
proteins that allow cells to recognize each other and contribute to proper cell differentiation and development.
gap junctions
allow for direct cell-cell communication. permit movement of water and some solutes (not proteins). each connexon (aka: gap junction) has six connexins.
tight junctions
form watertight seal to prevent paracellular transport or leakage of water and solutes. found in epithelial cells and form continuous band around the cell. cell-cell junction. (found in lining of renal-kidney- tubules where they restrict passage of solutes and water without cellular control)
desmosomes
bind adjacent cells by anchoring to their cytoskeletons. formed by interactions between transmembrane proteins associated with intermediate filaments inside adjacent cells. typically found at interface between two layers of epithelial tissue.
Hemidesmosomes
have similar function to desmosomes but their main function is to attach epithelial cells to underlying (basement) membranes
Function of cholesterol in membrane fluidity and stability
fluidity: interfering with crystal structure of the cell membrane and occupying space between phospholipid molecules
stability: cross-linking adjacent phospholipds through interactions at the polar head group and hydrophobic interactions at the fatty acid end
osmotic pressure equation
osmotic pressure = iMRT i- van't Hoff factor (number of particles obtained from the molecule when in solution) M- molarity of solution R- ideal gas constant T- absolute temp (K)
*Note: osmotic pressure is a colligative property
facilitated diffusion
simple diffusion for molecules that are impremeable to membrane (large/polar/charged molecules), using integral membrane proteins to serve as transporters or channels. energy barrier is too high for these molecules to cross freely.
carriers
ex of facilitated diffusion. only open to one side of the cell membrane at any given point, like a revolving door.
occluded state–> when the carrier is not open to either side
channels
facilitated diffusion. may have open or closed formation. when open they are open to both sides simultaneously.
secondary active transport
aka coupled transport. no direct coupling to ATP hydrolysis. uses every by one particle going down its electrical gradient to drive a different particle up its gradient. symport= same direction. antiport= opposite directions.
pinocytosis
endocytosis of fluids and dissolved particles. bulk movement of liquid into a cell through vesicular infoldings
phagocytosis
ingestion of large solids such as bacteria `
Nernst equation (determining membrane potential from intra- and extracellular concentrations of various ions)
E = 61.5/z log(ion out/ ion in)
Na+/K+ ATPase
maintain low concentration of sodium ions and high concentration of potassium ions in the cell (3Na out for every 2K in… makes cell more negative)
mitochondrial membranes
- outer- permeable to large pore allowing for passage of ions and small proteins. completely surrounds mitochondria
- inner- restricted permeability. has many cristae (infoldings) which increases surface area for integral proteins. encloses mitochondrial matrix (site of citric acid cycle)
goldman-hodgkin-katz voltage equation (intense Nerst)
takes every ion into account (Na+ K+ Cl-)
