2. (10) The proposal that membranes are bilayers of lipid molecules was a major

Question

2. (10) The proposal that membranes are bilayers of lipid molecules was a major step forward in understanding membranes. This concept is generally attributed to Gorter and Grendel Below are the original data from Gorter and Grendel s breakthrough 1925 paper entitled "ON BIMOLECULAR LAYERS OF LIPOIDS ON THE CHROMOCYTES OF THE BLOOD" (chromocytes are red blood cells,RBC). This paper purported to show that red blood cells were covered with a 2 molecule thick bilayer. They measured blood cells under a microscope to estimate surface area (RBC's are distinct in different animals, column 1) and numbers of cells (units in column 3 are mm3), then they extracted phospholipids with acetone from a large packed volume of cells column 2 units are mLs or cm3) and spread the lipids on a film balance to measure total surface area of the lipids as a monolayer (see below in final Column are m2). Based on the data were they justified? Choose two data sets and show why or why not with calculations. Watch units! BTW, their lipid extraction procedure with acetone was later shown to remove only about 75% of RBC lipid. How does this change the results? Discuss possible sources of error in these measurements and analysis

Explanation / Answer

Gorter and Grendel hypothesized that if plasma membrane is a bi layer then surface area of mono layer of lipids measured would be double. So they performed experiment and they extracted lipids from known number of RBC of many mammalian sources like humans, goat, sheep etc.

They finally after experiment calculated that lipids (monolayer) and plasma membrane are in the ratio 2:1. This supprted their hypothesis and led to conclusion that cell membranes are composed of 2 molecular layers.

Some of the experimental data was incorrect like miscalculation of area and pressure of lipid mono layer. It also failed to describe membrane function and false assumptions that plasama membrane consists of mostly lipids.

In their exoeriment they didnot extract completely all lipids from RBC and they underestimated surface of RBC because they are unaware of its double concave shape.

Acetone may induce oxidative stress leading to disturbance of bochemical and physiological functions of RBC thereby affecting membrane integrity.

Acetone results in RBC membrane destruction and haemolysis and increased blood levels which causes ketonemia.

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