describe the structure of the cell membrane?

Answer 1

For a mammalian cell the plasma membrane (outer membrane) is based on the fluid mosaic model. It is the physical barrier between inside the cell and out. It is the site of exchange with the external environment, the site of interaction and communication with the external environment and also provides structural support.

The Fluid-Mosaic Model - is a phospholipid bilayer, with proteins embedded in it. There are also cholesterol, carbohydrates which helps determine the function of the cell.

The function of the plasma membrane is dependent on the functions of the membrane proteins (transport, enzymatic activity, signal transduction, inter cellular joining, cell-cell recognition, and attachment to the cytoskeleton and extracellular matrix (ECM).

If you want any more information check out any anatomy and physiology or biology textbook, it should have a picture of the fluid mosaic model with a great description.

Answer 2

The cell membrane is a phospholipid bilayer. Phospholipids arrange them selves so that the polar ends face the solutions outside the cell and the cytoplasm. A phospholipid has a polar head connected to a phosphate group, glyceral and a non-polar tail(s). One tail is usually saturated while the other is unsaturated this helps the membrane remain fluid. Fluidity it vital for cell function. Proteins are also apart of the cell membrane and many remain fluid and move freely around the membrane but never flip. Cholesterol is also part of the membrane in animal cells and helps maintain fluidity. Attached to some phospholipids and proteins are sugars. These protect the cell and are involved in cell to cell recognition.

Answer 3

The Structure and Function of the Cell Membrane
The cell membrane is a fluid mosaic of lipids, proteins, and carbohydrates. In this tutorial we will describe these three structures and how they function in the cell membrane. This topic provides another example of the relationship between structure and function.

The Structure of Lipids
Lipids are the one class of large biological molecules that does not include polymers. They are grouped together because they share one important chemical property: they have little or no affinity for water. The hydrophobic behavior of lipids is based on their molecular structure. Although they may have some polar bonds associated with oxygen, lipids consist mostly of hydrocarbons. Smaller than true (polymeric) macromolecules, lipids are a highly varied group in both form and function, and include such things as waxes and certain pigments. In this tutorial we will focus on three classes of lipids: the fats, steroids, and phospholipids.
Fats (triacylglycerols)
Although fats are not polymers, they are large molecules, and they are assembled from smaller molecules by dehydration reactions. A fat is constructed from two kinds of smaller molecules: glycerol and fatty acids.

Glycerol is an alcohol with three carbons, each bearing a hydroxyl group. A fatty acid has a long, linear (unbranched), carbon skeleton, usually 16 or 18 carbon atoms in length. At one end of the fatty acid is a "head" consisting of a carboxyl group. Attached to the carboxyl group is a long hydrocarbon "tail." The nonpolar C-H bonds in the tails of fatty acids are the reason fats are hydrophobic: fats separate from water because the water molecules hydrogen bond to one another and exclude the fat.

In making a fat, three fatty acids each join to glycerol by an ester linkage, a bond between a hydroxyl group and a carboxyl group. The resulting fat, also called a triacylglycerol or triglyceride, thus consists of three fatty acids linked to one glycerol molecule. The fatty acids in a fat can be the same, or they can be of two or three different kinds. The length, number, and location of the double bonds in a fatty acid define its physical and chemical characteristics.

The terms saturated fats and unsaturated fats refer to the structure of the hydrocarbon tails of the fatty acids. If there are no double bonds between the carbon atoms composing the tail, then as many hydrogen atoms as possible are bonded to the carbon skeleton, creating a saturated fatty acid. The hydrocarbon tails can pack tightly together resulting in high melting points.

An unsaturated fatty acid has generally one to three double bonds at defined locations along the hydrocarbon chain. The fatty acid will have a kink in its shape wherever a double bond occurs that result in looser packing and lower melting points. This feature plays an important role in the relationship between temperature and the fluidity of the cell membrane.

The major function of fats is energy storage. A gram of fat stores more than twice as much energy as a gram of a polysaccharide, such as starch. In addition to energy storage, adipose tissue also serves to cushion vital organs, such as the kidneys, and provides insulation, by forming a layer of fat beneath the skin. This subcutaneous layer is especially thick in whales, seals, and most other marine mammals.

Phospholipids
Phospholipids are major components of the cell membrane. They are similar to fats, but have only two fatty acids rather than three. The third hydroxyl group of glycerol is joined to a phosphate group, which is negative in electrical charge. Additional small molecules, usually charged or polar, can be linked to the phosphate group to form a variety of phospholipids.

Phospholipids are described as being amphipathic, having both a hydrophobic and a hydrophilic region. Their tails, which consist of hydrocarbons, are hydrophobic and are excluded from water. Their heads, however, which consist of the phosphate group and its attachments, are hydrophilic, and have an affinity for water.

Because of their structure, when phospholipids are added to water, they self-assemble into aggregates so that the phosphate heads make contact with the water and the hydrophobic hydrocarbon tails are restricted to water-free areas. In the animation below you will see the formation of two such structures: micelle and the phospholipid bilayer.

Answer 4

A phospholipid bilayer -- the polar phosphate groups and attached groups on the surfaces and the polar fatty acids in the inside.