The process of cell metabolism is dependent on how a cell membrane behaves. The materials that move in and out of a cell are regulated by the materials that make up the membrane. Cholesterol's role in cell membrane function helps to keep this lining intact and assists with moving needed nutrients in and out of the cell.
Cholesterol is a fatty substance that's manufactured by the liver. It's classified as a type of lipid and can be found inside every cell in the body. A cell membrane is rich in cholesterol, which can make up as much as 50 percent of its content. The membranes that surround structures, or organelles, inside the cell also contain cholesterol. Cholesterol molecules are typically smaller and less dense than other surrounding molecules, so it only makes up about 20 percent of a cell membrane's mass, or weight.
The chemical makeup of cholesterol plays an essential role in how it helps the cell's membrane carry out needed functions. Each cell's membrane, also known as the plasma membrane, is composed of a double layer of phospholipids, proteins and cholesterols. A waterlike material fills each cell, and also fills the spaces in between a cell's internal structures. The materials that make up the plasma membrane each play a role in regulating what materials are able to move in and out of the cell.
Phospholipids are made out of fatty acids and phosphate heads, or compounds. As with most fatty materials, the fatty acid part of a phospholipid is water-insoluble, while the phosphate compound is water-soluble. The phosphate heads are situated on both the inside and outside of the cell membrane, whereas the fatty acids are only found on the inside of the membrane. Like phospholipids, cholesterol molecules are part water-soluble and part water-insoluble. This allows for both the water-soluble and water-insoluble components of phospholipids and cholesterols to interweave throughout the membrane's lining. By doing so they're able to regulate the types of materials that move into and out of the cell.
A cholesterol molecule is made up of a hydroxyl group, four hydrocarbon rings that surround the hydroxyl group and a hydrocarbon tail. The hydroxyl group is the water-soluble portion, while the hydrocarbon portions are water-insoluble. With the hydrocarbon rings situated on the outside, fatty acid chains coming off nearby phospholipids are attracted to the cholesterol molecules. This attraction helps to stabilize the membrane surface by holding it intact. In effect, cholesterol molecules help to maintain the membrane's durability so it can hold up to the continuous flow of materials that move in and out of it.
Cell proteins are essential to the life and function of a cell. Protein molecules come in different shapes and sizes depending on what type they are. Some protein molecules need to move in groups in order to function properly. When this is the case, a lipid carrier is needed to move these protein groups through the cell's membrane. These carriers are made out of high concentrations of cholesterols and phospholipids, with long fatty acid chains. These long chains reach all the way to the inside of the cell membrane and serve as a guide for the lipid carriers.