Chapter 8- Biological Membranes

Question 1

cell (plasma) membrane description

Answer 1

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

Question 2

glycoprotein coat

Answer 2

created by carbohydrates associated with membrane-bound proteins. cell wall also has high carbohydrate concentration.

Question 3

phospholipids and membrane dynamics

Answer 3

phospholipids move rapidly in the plane of the membrane through simple diffusion.

Question 4

Lipid rafts

Answer 4

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

Question 5

flippases

Answer 5

assist in transition or “flip” between layers–> movement of phospholipids b/w layers of plasma membrane b/c it is otherwise energetically unfavorable.

Question 6

fluidity of membrane

Answer 6

steroid and cholesterol molecules

Question 7

stability of membrane

Answer 7

waxes

Question 8

unsaturated fatty acids

Answer 8

come mainly from diet. transported from intestine to chylomicrons. increase membrane fluidity.

Question 9

glycerophospholipid

Answer 9

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.

Question 10

sphingolipids

Answer 10

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)

Question 11

cholesterol in membrane

Answer 11

20% of its mass. 50% mole fraction of membrane. adds fluidity to membrane. stabilizes adjacent phospholipds.

Question 12

waxes

Answer 12

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.

Question 13

3 main membrane proteins

Answer 13

1. transmembrane proteins- pass completely through the lipid bilayer (ex: channels and receptors)
2. embedded proteins- associated with only interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane (ex: catalytic activity with enzymes)
3. 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,

Question 14

carbohydrates and membrane

Answer 14

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)

Question 15

cell adhesion molecules (CAMs)

Answer 15

proteins that allow cells to recognize each other and contribute to proper cell differentiation and development.

Question 16

gap junctions

Answer 16

allow for direct cell-cell communication. permit movement of water and some solutes (not proteins). each connexon (aka: gap junction) has six connexins.

Question 17

tight junctions

Answer 17

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)

Question 18

desmosomes

Answer 18

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.

Question 19

Hemidesmosomes

Answer 19

have similar function to desmosomes but their main function is to attach epithelial cells to underlying (basement) membranes

Question 20

Function of cholesterol in membrane fluidity and stability

Answer 20

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

Question 21

osmotic pressure equation

Answer 21

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

Question 22

facilitated diffusion

Answer 22

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.

Question 23

carriers

Answer 23

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

Question 24

channels

Answer 24

facilitated diffusion. may have open or closed formation. when open they are open to both sides simultaneously.

Question 25

secondary active transport

Answer 25

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.

Question 26

pinocytosis

Answer 26

endocytosis of fluids and dissolved particles. bulk movement of liquid into a cell through vesicular infoldings

Question 27

phagocytosis

Answer 27

ingestion of large solids such as bacteria `

Question 28

Nernst equation (determining membrane potential from intra- and extracellular concentrations of various ions)

Answer 28

E = 61.5/z log(ion out/ ion in)

Question 29

Na+/K+ ATPase

Answer 29

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)

Question 30

mitochondrial membranes

Answer 30

1. outer- permeable to large pore allowing for passage of ions and small proteins. completely surrounds mitochondria
2. inner- restricted permeability. has many cristae (infoldings) which increases surface area for integral proteins. encloses mitochondrial matrix (site of citric acid cycle)

Question 31

goldman-hodgkin-katz voltage equation (intense Nerst)

Answer 31

takes every ion into account (Na+ K+ Cl-)