Lipids 2

Question 1

What are phospholipids?

Answer 1

Are amphipathic molecules
Contain phosphodiester bonds
Hydrophilic head consists of glycerol, phosphate group and variable group
Hydrophobic tail consist of 2 fatty acids

Question 2

What are the driving forces for phospholipid bilayer formation in water?

Answer 2

Van der Waal’s forces between fatty acid tails
Hydrogen bonds between hydrophilic groups
The hydrophobic effect - hydrophobic interactions in aqueous solutions are entropy driven and therefore thermodynamically favourable
Electrostatic interactions between hydrophilic groups

Question 3

What is the importance of forming bilayers rather than micelles?

Answer 3

Bilayers can be macroscopic but micelles only microscopic
Bilayers stabilised by non-covalent bonds therefore more stable
Bilayers self heal as free edges would expose hydrophobic chains to aqueous environment
Bilayers can readily form lipid vesicles (liposomes) and trap aqueous solutions inside

Question 4

How does cholesterol control membrane fluidity?

Answer 4

At body temperatures - cholesterol prevents phospholipids moving extensively throughout the membrane decreasing membrane fluidity
At low temperatures - cholesterol prevents phospholipids packing tightly together increasing membrane fluidity
Fluidity increased by the presence of unsaturated fatty acids
Hydrocarbon kinks prevent close packing

Question 5

Describe different types of membrane proteins and their function

Answer 5

Integral
Peripheral
Lipid anchored
Control entry and exit of molecules and information - pumps, channel, cell surface receptors
Contribute to cell identity and recognition

Question 6

What are glycolipids?

Answer 6

Glycolipids found on extracellular side of membrane
Act as mediators of cell-cell interactions
Act as markers of particular cell types