Cholesterol is a sterol made in animal cells. Sterols are molecules found in the cell membranes of plants. Sterols are basically steroid alcohols. Animal cells have cholesterol in the membrane and sterols in bilayers. Sterols occupy gaps left by kinks in the short-tailed hydrocarbon molecules. The short-tailed hydrocarbon molecules are essentially the HDL cholesterol or what is commonly known as good cholesterol. The chemical formula of a cholesterol molecule is C27H46O. Deposits of cholesterol appear as fatty layers and in common parlance are called lipids or fats.
Composition Of Cell Membrane
The cell is the basic unit of life. It is the smallest individually existing unit of life. Life on earth began from single-celled organisms like bacteria. Both animal and plant cells have cell membranes. Plant cells have an outer cover called a cell wall surrounding their cell membrane made of cellulose. Animal cells do not have cell walls.
A molecule is the smallest particle of matter that has independent existence. Still smaller particles of matter like atoms and sub atoms exist but they do not have an independent existence. Atoms combine to form molecules. By combining the atoms achieve stability and are able to exist independently as molecules. The cell membrane is richly supplied by cholesterol or C27H46O molecules. The body can manufacture own cholesterol molecules. Cholesterol is also present in most food matter consumed by the body. Cholesterol molecules make most of the cell membrane. The lipid, elastic and selective permissibility feature of cell membranes is because of cholesterol molecules in the cell membranes.
Normal structure of cell membranes
The normal structure of cell membrane is quite elastic, not rigid, and stretchable. High density cholesterol has been found to be more in normal cell membranes. The high density cholesterol accord the cell membrane with features suitable for carrying out its functions. High density cholesterol is the short tailed hydrocarbon. The kinks of the short tailed hydrocarbons are filled by sterols that further build up the structure of cell membranes and bi layers. The low density cholesterol is saturated hydro carbon with long tails and low combining capacity. These are not so efficient in giving the cell membrane the desired form.
Limp cell membranes
Limp cell membranes are poor in high density cholesterol. Limp cell membranes can have more content of other than HDL molecules like more of LDL molecules and sterol molecules. Limp cell membranes have inferior ability than normal cell membranes to carry out the cell membrane functions. Limp cell membranes can suffer from early death than cells with normal membrane structure. There can be early ruptures which might cause the cell organelles to release chemicals that dissolve them.
Fatty cell membranes
The cell takes up only so much cholesterol as is required by it to make the cell membrane and carry out intercellular functions. The extra cellulose molecules are not excreted by the body as are water soluble vitamins. They deposit as fat molecules around the cells and make the cells appear fatter than normal. Fatty cells collectively make up fatty tissues. Only when the fats are called up by the liver through activation of reverse transfer pathways they get used up as bile and can be excreted via fecal route.
Functions of cell membrane
The cells may almost appear as continuous mass except for the fine surrounding demarcations called cell membranes. The cell membranes enable bi way selective transfer of molecules between cells. When new cells are formed from existing cells by the process of cell division, the cell membranes conduct passage of nutrients to newborn cells from the parent cell. The cell membranes enable a phenomenon called osmosis that refers to selective transfer of fluids to and fro the membrane. Through the process of osmosis cells are able to derive nutrition and share excess nutrient molecules with surrounding cells. Thus a state of balance is achieved within all cells due to the selective permissibility of the cell membranes.
Cholesterol functions in the cell membrane
The cholesterol in the cell membrane achieve the following functions
- Structure of the cell and membrane
It is due to the presence of cholesterol molecules that cells get their structure. Cells with well-defined cell membranes exhibit distinct existence from surrounding cells. The presence of HDL in cell membranes accords them the required transmission capabilities to achieve balanced cell nutrition.
- Conduct of intercellular functions
An efficient cell membrane allows for the efficient conduct of intercellular processes with the cells. Within the cell, the cell organelles release chemicals and absorb molecules to synthesize and break down substances. A cell membrane of appropriate structure maintains boundaries and does not rupture untimely.
- Reverse transfer vehicles
HDL from cell membrane serves as vehicles for the reverse transfer of LDL to the liver where they get converted to bile. Thus HDL helps maintain the correct cholesterol balance and reduce excess LDL in the body.