L12 - Biological Membranes

Question 1

Importance of Biological Membranes

Answer 1

Compartmentalisation
Maintaining separate biochemical environments
Selectively permeable

Question 2

Fluid Mosaic Model Proof

Answer 2

Freeze fracture
Split bilayer with diamond knife

Question 3

Membrane fluidity

Answer 3

Movement,
Cholesterol,
Fatty acid unsaturation,
Protein movement,
Hop diffusion

Question 4

Movement in the Membrane

Answer 4

10^7 per second (2 microns per second) laterally
1x per month flip-flop

Question 5

Cholesterol’s role in the membrane

Answer 5

Reduces fluidity at high temperatures
Maintains fluidity at low temperatures

Question 6

Fatty Acid Unsaturation on Membrane Fluidity

Answer 6

Kinks prevent tight packing

Question 7

Protein movement in the membrane

Answer 7

Move laterally, proven by fusing mouse and human cells (fluorescent)

Question 8

Hop diffusion in the membrane

Answer 8

100x slower in natural membranes
Fenced in by actin cytoskeleton but can hop

Question 9

Integral proteins

Answer 9

Transmembrane

Question 10

Peripheral proteins

Answer 10

Loosely bound via other proteins

Question 11

Lipid-anchored proteins

Answer 11

Covalently attached to lipids

Question 12

Membrane carbohydrates

Answer 12

Short, branched oligosaccharides <15 sugar units
Identity tags
Most glycoproteins, some glycolipids

Question 13

Role of Selectively permeable barrier

Answer 13

Rate of diffusion based on size, relative solubility in oil

Question 14

Membrane transport proteins

Answer 14

Hydrophilic channels
Transport Proteins

Question 15

Roles of membrane proteins

Answer 15

Cell-cell recognition
Enzymatic Activity
Signal Transduction
Intercellular Joining
Attachment of cytoskeleton and extracellular matrix