What is a plasma membrane and how does it work 29

1
What is a plasma membrane and how does it work?
2/9

• What are the lipids in a membrane?
• What is membrane fluidity and what factors
  determine it?
• How is the lipid melting point affected by fatty
  acid tail length, polyunsaturation, trans-fats
  and sterols?
• What classes of protein are associated with
  membranes?
• What is a hydropathy analysis?
• Why cant some proteins move freely in the plasma
  membrane?

2
What is the current theory of the Fluid Mosaic
Model?Describe the evolution of ideas, the
names of these researchers, and their relative
dates. (7 ideas/dates)6 People/dates
3
What is membrane fluidity? Why is fluidity so
important?

• Fluid mosaic model wrt lipids and proteins
• Membrane lipid fluidity/motion
• PL Motion Flip-Flop vs. Lateral
  Diffusion
• Once/week vs.
  3-5 um/second
• Endoplasmic Reticulum
• PL translocation/translocase
• What is a membrane transition temperature? (Tm)

4
What things factor into estimates of membrane
fluidity?

• Why have a flexible membrane? Can it be TOO
  fluid?
• Permit conformational changes to membrane
  proteins!
• Flex without tearing PM!
• Regularity to PM permeability!
• PL density- /um2
• FA Tail length- long or short?
• Long Tail m.p. Short Tail -m.p.
• Unsaturated FA example omega fish oils
• Cis-natural vs. Trans-artificial
• Kinks No Kinks
• Lower Tm Raise Tm
• Ultimately many factors combine together!

5
Why do long FA tails make the fluid (melted)
state so tough to maintain?

• Rigid stacking
• Bilayer width
• Homeoviscous Adaptation
• Prokaryotes-
• Plants-
• Yeast-
• Each membrane PL ratio is unique!

6
The fluidity of a membrane is increased (M.P. or
Tm lowered) when The tail length is shorter OR
FA- tails are polyunsaturated
7
Different cells/organelles have unique membrane
lipid compositions to reflect different
requirements/environments!With respect to H2O
temp, what FAtail lengths are expected in
Antarctic Icefish (-3 C) or Devils Hole Pupfish
(40 C)?
8
Why do cis-bonds M.P. and trans-FA modify
fluidity?

• Cis-Fats creates spaces in the P.M.!
• Spaces in the P.M. create area for flex!
• FA Content Animal Fats vs. Vegetable Fats
• Problems and solution for industry?
• Trans fats DO NOT KINK!
• Trans fats in diet promote disease!
• Trans Fats are created to prevent rancidity!
• Trans Fats help keep margarine solid at Room Temp!

9
Sterols can either increase or decrease membrane
fluidity!

• Basic Shape
• Membranes are up to 50 sterol!
• As temp goes down OH inhibit tight PL-tail
  packing!
• As temperature goes UP- rings prevent PL
  Dispersion!
• CH also decreases PM permeability by filling in
  holes/spaces between FA tails!
• Sterols are produced by all eukaryotic cells!
• Especially in the human liver at night!
• WE need not have them in out diet (except Vit D)!

10
Membrane Flip-Flop Fast vs. SlowPhospholipid
diffusion across membrane
11
How do detergents work at the level of a lipid
bilayer?
12
How does membrane fluidity impact human disease?

• Coronary Heart Disease What are dietary risk
  factors?
• Cholesterol and Saturated fat
• Trans-fatty acids
• Fish Oils
• Fluidity Balance flexibility vs. membrane
  tearing in arterial wall and endothelial cells
  lining wall.
• Cell dysfunction and death!
• Neurological Function How diet affects nerve
  function?
• Cholesterol and permeability to ions like Na and
  K!
• Neuronal flexing and tearing?
• Links to hyperactivity and neurological
  degenerative diseases?

13
What are the classes of protein one finds
associated with the plasma membrane? Remember
that not ALL membrane proteins may be free to
diffuse about the membrane, some may be anchored
to a particular place.
14
Typically charges on amino (outside), carboxyl
(inside), and carbohydrate groups make membrane
protein flip-flip an extreme rarity!
15

• How do hydropathy analysis of a DNA sequence help
  us predict protein functions?
• Why is this useful?
• Human Genome Project and our proteins/diseases!

16
Are all the proteins associated with the PM
floating freely about the PM? Certainly
Not!Some proteins HAVE to be anchored in the
cytosolic side to certain locations by the
proteins actin, ankyrin, and spectrin!