The cell membrane is a vital component of any cell, and it has a variety of important functions. Cell membrane functions include maintaining the boundaries of the cells, thus supporting the contents of the cell, maintaining proper cell to cell contact, regulating the entry and exit of molecules in and out of the cell, etc. Thus, to understand how the cell membrane manages to carry out this procedure, one needs to understand the cell membrane structure. Given below are the various components that comprise the structure of the cell membrane according to the Fluid Mosaic model.
Structure of the Cell Membrane
The first layer of the cell membrane consists of a phosphid bilayer. The phosphate molecules are arranged in such a way that the hydrophilic heads are on the outside, while the hydrophobic fatty acid tails are on the inside, facing each other. The tails of the molecule are said to be hydrophobic and that is why they point inwards towards each other. This specific arrangement of the lipid bilayer is for the purpose of preventing the entry of polar solutes, like amino acids, proteins, carbohydrates, etc. Thus, the phosphate lipid bilayer is one of the main factors responsible for regulating the entry and exit of molecules in and out of the cell.
Integral Membrane Proteins
Integral membrane proteins are those proteins that are a part of the cell membrane structure. They are present between consecutive molecules of phopholipids. These fibrous proteins present may span the entire length of the cell membrane. These molecules have important functions, as they serve as receptors for the cell. Some of the proteins of the cell membrane may also enter the cell. Sometimes, a part of the protein molecule is inside and some of it is outside. This kind of protein molecules act as carriers for active transport of substances in and out of the cell. Some of these protein molecules form pores and thus, allow fatty acids and other lipid insoluble in water molecules to pass through. Furthermore, other integral proteins serve as channel proteins as well to aid in selective transport of ions in and out of the cell. Such molecules are visible with the help of an electron microscope.
Certain other elements may also be present along the length of the cell membrane, depending on the location and needs of the cell. These structures include globular proteins, which are peripherally placed, and are only at times associated with the cell. These protein molecules may even be enzymes or glycoproteins. In such cases, either the cell will have special functions, or the location of the cell may require it to perform certain specific functions. When speaking of plant cell vs animal cell, there is one important structure that is additionally present most of the time in animal cells. These molecules are cholesterol molecules, which aid the phospholipids in making the membrane impermeable to water soluble substances. These cholesterol molecules also stabilize the membrane and provide the cell with a 'cushion effect', which prevents it from suffering any major injuries due to trauma and impact forces.
Thus, this was a look at the various components that comprise the cell membrane structure and functions that it carries. The cell membrane of a plant or animal cell is akin to the skeleton in the human body, and hence, is the main component that forms the basic structure in all cells.