Lipids

Question 1

Basics about lipids

Answer 1

• Non-polar
• Doesnt make interactions with water
• Significantly hydrophobic

Question 2

Fatty acids

Two parts to them

Answer 2

• A long hydrocarbon chain - hydrophobic and not very chemically reactive, can be different in lengths and can be saturated (no double bonds) or unsaturated (one or more double bonds)
• A carboxylic acid group - hydrophillic and readily reacts with a hydroxyl or an amino group on a second molecule to form esters or amides

Question 3

Phospholipids

Answer 3

• Comprised of two fatty acids, glycerol and a phosphodiester head group

Question 4

Sphingolipids

Answer 4

• Has an amine so will be able to form amide bonds

Question 5

Steriods

Answer 5

• Type of lipid with a polycyclic aliphatic carbon skeleton
• They have a fixed shape due to cyclisation

Question 6

Self-assembly of amphiphiles (phospholipids)

Answer 6

• Monoglyceride - will pack in a sphere shape and form micelles with all the hydrophobic tails in the centre and the hydrophillic head on the outside
• Triglycerides - form bilayers with the heads on the outsides and the tails facing inwards and form cylinder shapes

Question 7

Lipid bilayer

Answer 7

• Has proteins (ion channels, receptors and transporters) in it as well as lipids and carbohydrates
• Provides the basic fluid structure and is relatively impermeable to most water-soluble molecules - less polar moelcules can pass
• Individual phospholipids can rotate axially or the fatty acid tails can flex

Question 8

Factors influencing fluidity in membranes

Answer 8

Fluidity decreases as the packing of phospholipids is closer
* Length - shorter, reduced interactions of hydrocarbon tails so more fluid
* Saturation - each double bond in an unsaturated tail creates a small kink , so less fluid
* Cholesterol controls fluidity as it can fit into the gaps of the unsaturated phospholipids, more cholesterol means less fluidity due tot he gaps being filled and more Van der Waal interactions