1. The Memrane Bilayer: Main Biophysical Properties Flashcards
What is the general membrane dry weight composition?
Protein - 60%
Lipid - 40%
Carbohydrate - 1-10%
What % of total membrane weight is water?
20%
What are amphipathic molecules?
Molecules with both a hydrophilic and hydrophobic moiety
What is the general structure of a phospholipid?
- 1 glycerol
- 2 fatty acids
- phosphate
- head group
What are the most prevelant carbon chains in a phospholipid?
C16 & C18
Why do phospholipids have a kink?
They contain a cis double bond
What is the typical carbon chain length range for a phospholipid?
C14 - C28
What head group does sphingomyelin contain?
phosphocholine head
What head group does a glycoprotein contain?
Sugar
What are the two types of glycoproteins?
- Cerebrosides
- Gangliosides
What head group does a cerebroside contain?
sugar monomer
What head group does a ganglioside contain?
Oligosaccharide (sugar multimer)
What are the 2 types of membrane structure?
- Lipid micelle (circle with heads facing out and tails in)
- Lipid bilayer (2 layers with heads facing out and tails in)
What are the 4 phospholipid motions?
- Flexion
- Rotation
- lateral diffusion
- flip flop
How does the cis double bond influence the bilayer structure?
Reduces the phospholipid packaging, so membrane is more permeable to substances
What is the role of cholesterol in the membrane?
To stabilise the membrane to prevent fracturing
What are the 4 types of membrane?
- Phospholipids
- Glycoproteins
- Sphingomyelin
- Cholesterol
What is the structure of cholesterol?
- Polar head
- Rigid planar steroid ring structure
- Non-polar hydrocarbon tail
How does cholesterol stabilise the membrane?
Reduces the influence of external factors that can alter the structure and/or fluidity of the membrane by abolishing the endothermic phase change during heating of the phospholipid by preventing the membrane from going into its crystaline state and from becoming too fluid
How is cholesterol inserted into the phospholipid bilayer?
Carbonyl oxygen on the fatty acid side chain hydrogen bonds to the hydroxyl group on the polar head group of the cholesterol
What are the effects of cholesterol insertion in phospholipid bilayers?
Reduces fluidity - Reduces phospholipid chain motion by attaching a rigid structure to it
Increases fluidity - reduces the phospholipid packaging by increasing the distance between each phospholipid
What are the general functions of biological membranes?
- Highly selective permeable barrier
- Communication
- Signal generation in response to a stimuli
- Control of enclosed chemical environment
- Recognition (signaling molecules): adhesion proteins & immune surveillance
Are all membranes the same?
No each has a different structure and therefore a different function
e.g. secretion, transportation, absorption of biody fluids, etc.
