A soap molecule has a long hydrocarbon chain and a charged head. Soap will form a mono-molecular film on water.

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Agitating soapy water makes micelles.

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Soap bubbles are made from a double layer of soap

molecules sandwiching a thin layer of water.

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Phospholipids, the main component of cell membranes,behave like soap molecules.

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hydrophobic tails

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IntroductionA thin outer layer called the cell membrane surrounds all

cells.

This membrane has four main functions:1. allow the transport of raw materials into the cell2. allow the transport of manufactured products and wastes

out of the cell3. prevent the entry of unwanted material into the cell4. prevent the leakage of essential matter out of the cell

IntroductionCellular functions depend on a watery

environment like the one that is found on the inside of the cell.

In order to maintain their integrity, cells need to be surrounded by an environment through which water cannot flow. A membrane composed of fatty molecules serves this purpose.

History of the Cell MembraneIn 1924, using an

electron microscope, two Dutch physicians, E. Gorter and F. Grendel found that the cell membrane was composed primarily of phospholipids (shown on the right).

History of the Cell MembraneThey deduced, based on the

properties of phospholipids, that the cell membrane was in fact a bilayer.

water of the extra-cellular fluid

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water of the cytoplasm

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History of the Cell MembraneCell membranes form because

these phospholipid molecules spontaneously orient themselves in a double layer having a fatty inside and a water soluble outside.

water of the extra-cellular fluid

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History of the Cell MembranePhospholipids are made

up of a glycerol backbone with a hydrophilic head region containing a phosphate group and a hydrophobic tail region containing a saturated fatty acid and an unsaturated fatty acid.

The fact that it has both types of fatty acids ensures the cell membrane is fluid.

History of the Cell MembraneBy the 1930s

experimental evidence showed that proteins were also part of the cell membrane.

In 1935, James Danielli and Hugh Davson proposed the sandwich model: a phospholipid bilayer between two layers of protein with pores for molecules to travel through.

History of the Cell MembraneStronger electron microscopes would show

that the cell membrane was not covered in protein, but rather had protein embedded in it.

History of the Cell MembraneIn 1972, S. J. Singer and Garth Nicholson

presented the fluid mosaic model of the cell membrane, which displayed the cell membrane as an integration of proteins and other molecules into the phospholipid bilayer.

Structures in the Fluid Mosaic Model of the Cell Membrane

Cholesterol is interspersed throughout the cell membrane to add rigidity to it.

It also allows the cell membrane to stay fluid over a wider range of temperatures.

Structures in the Fluid Mosaic Model of the Cell Membrane

Various proteins are associated with the cell membrane.

1.Integral Proteins (a.k.a. trans-membrane proteins) span the width of the cell membrane and create channels through which charged molecules or large molecules can pass through.

2.Peripheral Proteins are found on the surface of the cell membrane and are primarily used in cell to cell signaling with surface carbohydrate chains or linking with the cytoskeleton for support.

Structures in the Fluid Mosaic Model of the Cell Membrane

The cytoskeleton is attached to the cell membrane for added stability, since membrane proteins and phospholipids can shift places in the membrane.

The Fluid Mosaic Model