BIOC 503 - Membrane Dynamics

fluidity, change shape

__ and the membrane’s ability to ___ are necessary for cell function because

localized

___ motion (nanoseconds scale)

• rotational

• rotation around bonds

• bobbing at water-lipid interface

Does not change location of molecule within the membrane. Rely on membrane fluidity.

extensive

___ motion (milliseconds to hours)

• lateral mobility

• transverse mobility

Change of location of molecule in the membrane: diffuse from one place to another or switch from one monolayer to the other. Rely on the ability of membrane to change shape.

gel state

state of fully saturated lipid bilayer when there is not enough fluidity

fluid state

state of a fully saturated lipid bilayer when there is enough/too much fluidity

• can become leaky in that state

factors affecting membrane fluidity

• temperature

• cholesterol

• saturation

cold

__ temperatures lead to a crystalline structure of lipid bilayer thus ending up in a gel state

hot

__ temperatures lead to a liquid crystalline structure of lipid bilayer thus ending up in a fluid state

double bonds

saturation affects membrane fluidity: ___ in 2nd position makes membrane MORE fluid by enhancing the rotation of lipid molecules in bilayer.

• polyunsaturated fatty acids (omega 3 and omega 6) crucial to membrane fluidity

cholesterol

___ when in lipid bilayer in high amounts makes the membrane LESS fluid

• take up the space created by the double bonds of fatty acids

• small polar headgroup in monolayer surface while large hydrophobic body with fused rings is inside bilayer

lipid rafts

mobile microdomain of the plasma membrane containing more saturated fatty acids, cholesterol, and sphingolipids

• more rigid than rest of membrane

prokaryokes

__ do not have cholesterol and thus control membrane fluidity by regulating unsaturation of fatty acids

lateral diffusion

uncatalyzed ___ of membrane lipids from one place to another on the SAME leaflet

• fast & with low resistance

• NO ENERGY REQUIRED aka ATP independent process

• most active motion in bilayer

flip-flop

uncatalyzed ___ between two leaflets is a very slow process

• transverse motion = change in monolayer

• ATP DEPENDENT PROCESS
  requires special transmembrane proteins/transporters to move hydrophilic head through the hydrophobic inside of bilayer

flippase

P type ATP transferase moving PE and PS from the outer to inner monolayer

• transverse motion = change of monolayer

• slow process

• ATP dependent

floppase

ABC transporter moving phospholipids from inner to OUTER monolayer

• transverse motion = change of monolayer

• slow process

• ATP dependent

scramblase

transmembrane protein moving lipids in EITHER direction, toward equilibrium

• use the energy of the gradients to function

• activated by Ca2+

fluorescence recovery after photobleaching

aka FRAP

Technique used in the experiment demonstrating lateral mobility of phospholipids where light was used to take away the fluorescence in a specific spot which was then monitored over the next few seconds it took for fluorescence to recover

proteins

membrane ___ CANNOT flip-flop aka cannot change monolayer as they need to be specifically oriented to functions

HOWEVER, they can diffuse laterally by their interactions with cytoskeletal structures and ECM

• process SLOWER because they are complexes with multiple subunits and have intracellular domains interacting with other molecules

hybridized cells

experiment technique used to demonstrate the lateral diffusion of PROTEINS in plasma membrane where mouse cell and human cell experimentally merged before being analyzed for membrane composition.

sialic acid receptor

receptor for viruses triggering endocytosis by host cell

lowest energy

a protein with intrinsic curvature interacts strongly with curved membrane surface, allowing both membrane and protein to achieve their ___

superstructures

if membrane region spontaneously curves, monomeric subunits of certain proteins can polymerize into ___ that favors and maintains curvature

amphipatic helices

A protein with one or more ___ inserted into one leaflet of the bilayer crowds the lipids in that leaflet, forcing the membrane to bend.

Caveoloe

small, flask-shaped invaginations of the plasma membrane in vertebrate adipocytes

• markers for fatty tissues

• contain specific protein called caveolin

caveolin

protein specific to caveolae forcing inward curvature of the plasma membrane

• usually dimer

• each half of dimer has 3 fatty acids chain going into the membrane from the INNER monolayer