Topic 1.3 Membrane Structure

Question 1

What was the Davson-Danielli Model

Answer 1

• suggested a lipid-protein sandwich because proteins appear darker in electron micrographs and phospholipids appear light. The proteins coat the outer surface and do not permeate the bilayer. (a trilaminar appearance)

Question 2

What did the Davson-Danielli model not account for and wrongly assume

Answer 2

• assumed all membranes were uniform thickness w a constant lipo-protein ratio
• did not account for permeability of substances (e.g. hydrophilic)
• assumed all membranes would have symmetrical internal and external surfaces
• the temperature of solidification did not correlate with the proposed model

Question 3

Evidence for the Falsification of Davson-Danielli

Answer 3

1. red-green fluorescent antibody tagging: membrane proteins from two diff cells w diff color, when the two cells fused, the red and green markers became mixed throughout, suggesting that membrane proteins could move
2. free-fracturing to split the membrane revealed irregular rough surfaces within; rough surfaces interpreted as transmembrane proteins

Question 4

emergent property of putting phospholipids into water?

Answer 4

they automatically arrange themselves into a spherical shape to keep the heads ‘wet’ and the tails ‘dry’