(b)+Membrane+Structure

MEMBRANE STRUCTURE By Kelly E. and Sarig C.

=THE JOBS OF THE PLASMA MEMBRANE:=
 * Isolate the cytoplasm from the external environment
 * Regulate the exchange of substances
 * Communicate with other cells
 * Identification
 * Hold the cell together
 * Protect the cell
 * BInd to other cells and molecules
 * Site for biochemical reactions

=PHOSPHOLIPIDS:=
 * Contain a hydrophilic (attracted to water) head and a nonpolar(prefer other neutral molecules) hydrophobic (repelled from a mass of water) tail
 * The polar head group contains one or more phosphate groups
 * The hydrophobic tail is made up of two fatty acyl chains
 * When many phospholipid molecules are placed in water, their hydrophilic heads tend to face water and the hydrophobic tails are forced to stick together, forming a bilayer
 * Phospholipids are not bonded to each other which makes the double layer fluid



= = = =

= = = = =THE FLUID MOSAIC MODEL=

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The plasma membrane structure is called a //fluid mosaic// because it is made up lots of //phosploipids// that can move laterally thoughout the structure. It is 2 phospholipds thick (phospholipid bi-layer). With the //hyrdophilic// //phosphate// heads on the inside and outside of the cell, and the //hydrophobic hydrocarbon// tails inbetween the two. The phospholipds are bonded together with hydrogen bonds. The result of all this being the fluid mosaic can change shape very easily with out rupturing. When the plasma membrane ruptures the phospholipids will automatically being to 're-group' because their tails repel water as their heads attract it.

=PLASMA MEMBRANES AND MEMBRANE PROTEINS= =INTEGRAL PROTEINS & PERIPHERAL PROTEINS:=

There are two type of membrane proteins (integral and peripheral). Integral proteins are proteins that pass through the entire membrane (they act as tranport channels). The peripheral protein, on the other hand, are proteins that only passes through one layer of phopholipids (it acts as a recognition site). Peripheral proteins contain carbohydrates to help in cell to cell recognition. =KEY FUNCTIONS OF THE MEMBRANE PROTEINS:= =﻿=
 * Structural Proteins are attacked to microfilaments to ensure stability of the cell.
 * Cell adhesion molecules allow cells to interact with and identify each other.
 * Membrane enzymes produce substances that allow the cell to function properly.
 * Membrane receptor proteins serve as a connection between the cell's internal and external environment.
 * Transport proteins play an important role in the maintenece of concerntration of ions. They come in two forms: carrier proteins and channel proteins.