Lipids and Cell Membranes

Question 1

What is a lipid?

Answer 1

A lipid is a molecule that has low solubility in water

Examples:

• Phospholipids (make up the cell membrane)
• Fats (energy sotrage)
• Sterols (e.g.: cholesterol)
• Some vitamins

Question 2

Function of lipids

Answer 2

• Sources of energy
• Form membranes
• Participates in cell signallin

Question 3

What is the length of fatty acids?

Answer 3

6-24 carbons - naturally occurring fatty acids have always even numbered carbons

Question 4

What are fatty acid nomenclatures?

Answer 4

Describes the degree of unsaturation and position of the double bonds

• Delta numbering starts at COOH
• Omega numbering starts at the first double bond of the methyl group

Question 5

What do sterols make up?

Answer 5

• Bile acids
• Steroid hormones
• Vitamins
• Cell membranes

Question 6

Describe the structure of sterols

Answer 6

Rigid, strong, flat, ring structures

The only polar part of the molecule is the -OH bond - rest is non-polar and hydrophobic

Question 7

List a few inherited disorders in lipid pathways

Answer 7

Gaucher’s - genetic disorder in which the metabolism and storage of fats is abnormal

Niemann Pick - inherited, sever metabolic disorder

Tay-Sachs - genetic disorder causing progressive damage to the nervous system

Question 8

What are the three types of membrane lipids?

Answer 8

Phospholipids

• Glycerophospholipids - hydrophilic
• Choline/ethanolamine/serine/inositol; phosphate, glycerol backbone, 2 fatty acid chains

Glycolipids

• sphyingolipids
• alcohol, phosphate, sphingosine core, fatty acid

Question 9

Meaning of amphipathic?

Answer 9

Having both hydrophilic and hydrophobic parts

Membrane lipids are usually amphipathic

Question 10

Why are membranes curved into the shape of a sphere?

Answer 10

When flat, the hydrophobic edges would interact with water - when curved up, there are no edges

Question 11

Describe the movements of phospholipids

Answer 11

Can be:

• Lateral - multiple times every second
• Rotational - once every month, lipids move from one leaflet to another

Question 12

What structural feature affects the fluidity of phospholipids?

Answer 12

The number of kinks they have - the more they have, the more unsaturated they are aka the more fluid they are

Question 13

What is the experiment used to check how fluid phospholipids are?

Answer 13

Fluorescence recovery after photobleaching (FRAP)

• Since membrane phospholipids move constanty they will eventually take over the space that was destroyed
• The more fluid there is in the membrane, the quicker it recovers

Question 14

What happens when cholesterol becomes wedged between phospholipids?

Answer 14

The membrane stiffens and becomes less fluid

Question 15

How is membrane asymmetry generated?

Answer 15

Flippase transfers lipids to the other leaflet by rotating and physically knocking the phospholipids aside

Question 16

How are new membranes produced?

Answer 16

New membranes are synthesised in the ER and then are transferred to the other parts of the cell through vesicle trafficking

Question 17

Types of membrane proteins

Answer 17

Transmembrane proteins
- the proteins can creat channels and pores through membranes

Membrane associated proteins

• partially in membrane;
• e.g.: Pleckstrin homology domains (PH) - 100 amino acid region, found in many proteins, that binds to certain type of phospholipid

Lipid-linked proteins

• lipids are bound by covalent bonds
• GPI-anchors - glycosylphosphatidylinositol

Protein-attached proteins

• especially important in signal transduction
• Has a Beta-2 adrenergic receptor/G-protein coupled receptor
• Has a G protein signalling complex, of which when one part comes away, it activates processes