Chapter 6 (Bio-2210)

what does membrane function depend on

them being dynamic structures, Fluidity and functional proteins

Current membrane model

fluid mosaic

how much of membranes are proteins

~50-75% by weight

fluid part of the model

membrane lipids

phospholipids

most abundant lipids in the membrane

glycolipids

have specialized functions in the membrane

sterols

stabilize membranes and buffer fluidity

movement of lipids in membrane

rotation and lateral id rapid and random

tranverse is rare and regulated

phase transition

when the membrane goes from a fluid state to a gel state

transition temperature

the temperature in which the membrane becomes fluid

below to T_m

the functions relying on fluidity of membrane will be disrupted

Unsaturated fatty acid fluidity

more fluid, more points of unsaturation mean more fluid

saturated fatty acid fluidity

not fluid, solid at room temp

length of fatty acids in fluidity

longer chains decrease fluidity

Fluidity buffer

maintains membrane fluidity in response to temperature change

cholestral in high temperature

stabilizes the membrane

cholestral in low temperature

prevent the lipids from packing tightly together, makes them less gel like

Homeoviscous adaptation

change in length and degree of saturation of fatty acids to compensate for temperature changes, common in ectotherms

mosaic part of the membrane

the proteins

integral membrane proteins

embedded in the lipid layer

• have hydrophobic domains

• can move laterally in the membrane

the orientation of integral membrane proteins

• regions exposed to one sid eof the membrane are chemically different then the other side

• all the molecules are orientated the same way

Peripheral proteins

located on one side of the bilayer

Lipid-anchored proteins

covalently attached to lipid molecules embedded in the bilayer

functions of membrane proteins

1. enzyme catalysts

2. transport proteins

3. anchors

4. receptors

5. communication

Glycosylation

linkage of a carbohydrate to a protein to make a glycoprotein

functions of glycoproteins

• glycoproteins are most prominant in plasma membrane

• the carb groups lay on outer surface of the membrane

• important for cel-cell recognition and signalling