Membrane Structure and Function Flashcards
Most abundant lipids in membranes =
phospholipids
Phospholipid Composition
Polar Head =
1) Glycerol backbone
2) Phosphate Group
3) Side Chain (off of phosphate)
Hydrophobic Tails =
1) Fatty acid chains (2)
Phosphate
PO4 -
–> Charged group
Ampiphatic
Meaning to have BOTH hydrophilic and hydrophobic regions
(like phospholipids do)
Saturated
ONLY single bonds (has greater rotation)
1) Physically more rigid
2) More compact
3) Can fit more into one unit of volume
Unsaturated
Contains double bond/s (has less rotation at sites of double bond)
1) Physically less rigid –> More fluid
2) Has “kinks”
3) Can’t stack well
Saturation of phospholipids exist in a…
RANGE –> More of a “dimmer switch” analogy rather than a traditional light switch
The plasma membrane is a…
Phospholipid bilayer
Phospholipid Bilayer
A double layer of phospholipids in which the polar heads face out and the tails face in (to each other)
The bilayer structure of membranes creates…
A membrane that is an effective cellular barrier
–> The membrane is largely impermeable to charged/polar molecules
The membrane is impermeable to charged/polar molecules because…
Of the ampiphatic nature of the phospholipids and their created bilayer
–> Charged/polar molecules cannot pass (diffuse ) through the hydrophobic interior of the membrane
Fluid-Mosaic Model
Fluid = Refers to phospholipids
Mosaic = Refers to proteins
“A mosaic of protein molecules bobbing in a “fluid” bilayer of phospholipids”
Distribution of proteins in a membrane is…
NOT random
–> Groups of proteins are often associated in long-lasting, specialized patches where they carry out common functions
Fluidity of Membranes
Membranes are not static sheets of molecules locked rigidly in place
–> It is dynamic, it moves
Lateral Movement
Side to side movement of lipids in a membrane
–> Very frequent, rapid
–> “Like partygoers elbowing their way through a crowd”
2 types of membrane movement:
1) Lateral movement
2) Flip-flop movement
Flip-Flop Movement
When a lipid switches sides across the membrane (to the opposite layer)
–> Very rare, but can happen
Issue of the flip-flop movement is…
Very difficult to do as the polar head must enter the non-polar region of the bilayer to come out the other side
–> Requires A LOT of energy to do so
Do proteins move in membranes?
YES, they can but many do not
Moving Proteins
–> Proteins move at a much slower rate than lipids (due to larger size)
Types of protein movement in membranes
1) Highly directional manner
2) Simply drifting in the membrane
Non-moving Proteins
Many membrane proteins do not move as they are bound/fixed by the ECM or cytoskeleton
What does the fluidity of a membrane depend on?
Composition AND temperature
> # Unsaturated Phospholipids =
Increase in fluidity (close packing is not as possible)
Unsaturated phospholipids solidify at…
Lower temperatures
–> Lower freezing point