Lecture 10 Key experiments in PM chemistry, the Fluid Mosaic Model

Extracellular matrix structure

Proteoglycans: a complex web of glycoproteins

Collagen(protein)

elastin( another component)

Fibronectin: bond the ECM glycoproteins to integrins(protein of the plasma membrane) that at in the plasma membrane and extend to the cytoskeleton filaments

Significance of Plasma Membrane

*Creates a barrier that defines the inside and outside of the cell

-selective barriers(regulates transportation of material in/out of cells

-phospholipid bilayer

What wasn’t know about membrane structure

-did not know how phospholipids were arranged in the membrane

Role of Evert Gorter

-conducted an experiment with red blood cells to determine if phospholipid membranes were 1 or 2 thick

Why were red blood cells used

-easy to obtain

-easy to count

-mature cell membranes eject everything expect for plasma membrane

-uniform in size( throughout different species all the same size)

-lack nucleus, organelles, and other complex membranes

Gorter Experiment with Red Blood Cells

1.collected and counted red blood cells

2.Calculated the total surface area of red blood cells

2. cells were destroyed(lyse) and collected the phospholipids (chemical separation)

3. phospholipids were placed into a chamber of liquid buffer that created a floating monolayer

4. measured the total surface area of phospholipids and compared it to total SA of red blood cells

Conclusion of Gorter’s Experiment

Two possible outcomes:

1. surface area of the monolayer equaled the surface area of cells

2. surface area is 2x the surface area of the cells

Conclusion:

*surface area of monolayer was 2x surface area of cell( 2:1 ratio)

-cell membranes are bilayer

Two types of plasma membrane proteins are..

Transmembrane protein: help with transport, float in lipid bilayer, pass in bilayer

Peripheral protein: embedded in membrane, attached to the surface of the membrane

Fluid Mosaic Model of Membranes

-plasma membranes are fluid structures

-things are floating around in it the plasma membrane

Evidence for Membrane Fluidity

Cell Fusion experiment

-membrane of proteins were stained with fluorescent dyes

-test human(red) and mouse cells( green)

Observations

-would colors stay in place?

-do colors mix?

Cell Fusion Experiment

-over time, the colors diffused laterally