membrane proteins

Question 1

liquid-ordered (Lo) state

Answer 1

gel-like state in which all types of motion of individual molecules are strongly constrained

Question 2

liquid-disordered (Ld) state

Answer 2

state in which individual hydrocarbon chains are in constant motion (lateral & rotational)

Question 3

membrane dynamics

Answer 3

at mammalian physiologic temperatures (20-40 C) biological membranes are fluid and are maintained in a transition state between Lo & Ld

Question 4

membrane proteins facilitate…

Answer 4

translocation of individual lipid molecules

Question 5

flippase

Answer 5

(P-type ATPase) moves PE and PS from outer to inner leaflet

Question 6

floppase

Answer 6

(ABC transporter) moves phospholipids from inner to outer leaflet

Question 7

scramblase

Answer 7

moves lipids in either direction, toward equilibrium

Question 8

membrane proteins are limited in movement by:

Answer 8

associating to form large aggregates (patches)
anchoring to internal structures

Question 9

microdomains (rafts)

Answer 9

clusters of cholesterol and sphingolipids that make the bilayer slightly thicker and more ordered than neighboring, phospholipid-rich regions- can be up to 50% of the cell surface

Question 10

_______________ are central to the ability of biological membranes to undergo fusion with other membranes w/o losing continuity

Answer 10

curvature changes

Question 11

integrins

Answer 11

surface adhesion proteins that mediate a cell’s interaction with the extracellular matrix and with other cells
-> carry signals in both directions across membrane
-> heterodimeric proteins composed of two unlike subunits, a & B

Question 12

cadherins

Answer 12

involved in surface adhesion
-> undergo homophilic interactions with identical cadherins in an adjacent cell

Question 13

selectins

Answer 13

have extracellular domains that bind specific polysaccharides on the surface of an adjacent cell
-> requires Ca2+
-> essential part of the blood-clotting process

Question 14

passive transporters

Answer 14

facilitate movement down a concentration gradient, increasing the transport rate
-> process is called passive transport or facilitated diffusion

Question 15

active transporters

Answer 15

move substrates across a membranes against a concentration gradient or an electrical potential; process called active transport

Question 16

simple diffusion

Answer 16

movement of a solute from the region of high concentration to the region of lower concentration

Question 17

membrane potential, Vm

Answer 17

a transmembrane electrical gradient that occurs when ions of opposite charge are separated by a permeable membrane

Question 18

transporter proteins reduce the energy of activation for diffusion by…

Answer 18

forming noncovalent interactions with the dehydrated solute; providing a hydrophilic transmembrane pathway