Lecture 7 - Membrane Structure

Question 1

What are the functions of biological membranes?

Answer 1

1. Selective permeability barrier
2. Comparmentalization of functions.
3. Identification
4. Signalling
5. Energy storage

Question 2

What are common features of biological membranes?

Answer 2

1. Sheetlike structures that can form closed boundaries in aqueous solution
2. Composed of lipid, protein, and carbohydrate
3. Lipid bilayer is relatively impermable to polar molecules
4. Membrane proteins carry out most specific fxns
5. Membranes are held together by non-covalent interactions
6. Biological membranes are asymmetric
7. Membranes are fluid under physiological conditions

Question 3

Membrane lipids are …..

Answer 3

AMPHIPATHIC! - both hydrophobic (hydrocarbon tails) and hydrophilic (polar head groups)

Question 4

Describe the structure of a phospholipid

Question 5

Describe the effect of saturation and length of fatty acids chains

Answer 5

Increased saturation and increased length leads to decreased fluidity

Question 6

What confirmation are naturally occuring unsaturated fatty acid chains in?

Answer 6

CIS

Question 7

Describe the general structure of phospholipid backbone and give examples.

Answer 7

Glycerol or sphingosine (in sphingomyelin) - attach to fatty acids and phosphate via hydroxl groups

Glyercol attaches to 2 fatty chains, sphingosine carries on hydrocarbon of its own

Question 8

What composes a phospholipid headgroups and give some examples

Answer 8

Phosphate + alcohol, ex. serine, choline, inositol, ethanolamine, etc.

Question 9

What are other components of the membrane?

Answer 9

Glycolipids - sphingosine backbone w/ sugar attached

Cholesterol - makes membrane less flexible

Question 10

Memorize the amphipathic properties of membrane lipids…

Answer 10

Question 11

What are the forces at play in the spontaneous formation of lipid bilayers?

Answer 11

Hydrophobic effect, van der Waals, electrostatic and H bonding

Question 12

What is the difference between transverse and lateral diffusion of membrane lipids

Answer 12

Transverse (flip flop) - very slow, protein mediated

Lateral - all the fucking time, gives fluidity

Question 13

What are factors affecting fluidity?

Answer 13

1. Temp - needs to be above “melting temperature” to be fluid and free flowing
2. Length and degree of unsaturation of fatty acid chain - shorter, unsaturated = ^^ fluidity
3. Cholesterol content - decreases fluidity (lipid rafts)

Question 14

What factors make a substance imperable to a lipid bilayer?

Answer 14

1. Polarity - ^ polarity means it won’t get through
2. Size - the larger the molecule, the more difficult it will be to get through

Question 15

How do drugs get into cells?

Answer 15

1. Passive diffusion
2. Hijacked transporters
3. Liposome delivery
4. Protein transduction

Question 16

What is the relative ratio of lipid to proteins in the membrane?

Answer 16

Differs but around 1:1, there’s more protein than people think

Question 17

Types of membrane proteins…

Answer 17

Integral membrane proteins - transmembrane, monolayer associated, lipid linked - amphipathic to be inserted into membrane

Peripheral membrane proteins - protein attached

Question 18

Fluid mosaic model

Answer 18

1. Lipid bilayer acts as solvent for membrane proteins
2. Membrane proteins are free to diffuse laterally, but cannot flip-flop

Question 19

How can lateral diffusion of membrane proteins be constrained?

Answer 19

1. Anchoring protein to intracellular structure
2. Anchoring protein to extracellular structure
3. Protein/protein interactions b/n cells
4. Barriers by junction proteins

Question 20

Describe lipid rafts

Answer 20

Regions of membrane that are more rigid and resistant to solubilization

Specific proteins are recruited for…

1. Signal transduction
2. Protein sorting
3. Recognition
4. Viral entry/exit

Question 21

Describe some special properties of lipids in a membrane

Answer 21

Abnormal lipid distribution signal cells are dying