Membranes pt. 1

no cell

• cell membrane (plasma membrane)
• mid 1800s 
• something had been surrounding cell 
• --> definite boundary

• interaction with environment
• internal structures
• boundary to separate mixing between environments

• compartmentalize (prevent mixing between cytoplasm and environment)
• with the composition of membranes
• (phospholipids, steroids, carbs, proteins)

lipids

• 1890s
• doctorate in botany; interested in what's around the cell
• theory: whatever was in the boundary of the cell would affect what goes in and the rate 
• found that lipid-soluble molecuels moved into cell much more rapidly compared to polar, insoluble substances
• some ort of lipid was on surace

• Hober: 1910
• Fricke: 1925
• interest: RBC; interested in electrical resistance/ conductivity of cell; if you measure cell resistance, will contents of cell be resistant or attracted (it would conduct because of hte charge of the many particles,)
• they found that in intact cells, resistance was high; conductivity was low
• suggested it was due to lipids

• proteins
• polar and highly conducting

• conductivity
• lipid

• Harvey: 1912
• Collander: 1927
• not working together
• worked with artificially prepared protein membrane
• interested in movement through the membrane
• found htat the membrane wsn't as permeable as what was on the surface of the cell
• supported lipid idea
• whatever was on surface wasn't just protein

put drop of lipid on lside next to surface of amoeba cell--> began to spread out on the surface after sticking to cell

• late 1915-1920
• physical chemist
• interested in monolayers and phospholipids
• studied behavior of phospholipids
• designed Langmuir trough to study lipids
• mix lipids in benzene: as benzene evaporated, lipids would spread self over surface--> arranged self in monolayer
• - measure SA with that

if lipids were on cells and if so, how many layers

• 1925
• used mammal RBCs since they are hollow--> made RBC ghosts (all you see are the plasma membranes/ made by putting it in hypertonic solution
• took RBCs, extracted lipid, put it in a trough, squeezed it, and measured SA of lipid and RBC and compared

• phospholipd: RBC= 2:1
• 0 used acetone, which only takes 2/3 of phospholipids
• - used dry preparations, which caused lower yield due to shrinking

• mid 1930s
• RBC ghosts, looking with polarized light (all wavelengths in same direction)
• suggested lipid molecules are all perpendicular to the plane of the membrane

• 1931
• yes
• studied surface tension of cell, where it meets water

• kind of measurements for cells for about 0.2 dyne/cm (measure of surface area)
• oil was also measured (10-15 dynes per cm)

• told us that membrane can't just be lipid
• cause if it were, the surface tension value would be similar to oil

• they added protein which brought the value near 0.2 dynes per cm
• the idea that proteins had to be involved in lipids

• alot
• proteins
• specific
• can work on things
• molecules similar in structure won't get through as easily as other molecules (which suggested presence of proteins)

• they did but there were serious problems:
• - how do you know you're not dealing with more than the membrane?

contamination

membranes of different speicies and types of cells leads to different results and questioning of results

even if working with the same types of cells fromt eh same organism, the fact that they may have been in a different environment could have changed the results

batch of cells from same environment, but different preparation--> different results

animal membranes

lipid composition