Explain how the molecular structure of cell membranes accounts for Essay

Explain how the molecular structure of cell membranes accounts for their selective permeability - Essay Example Other than proteins and lipids the cell membrane also consists of carbohydrates which form a layer outside the cell membrane to serve specific functions of the body. The proteins have a very important role to play in maintaining the shape of the cell membrane which is crucial for maintaining the form and working of the cell as well. They have other important roles not only restricted to the maintenance of functioning and integrity of cell membrane but also in the intracellular metabolic activities. This is because proteins act as receptors for several hormones as well as transmitters which then alter the metabolic activities taking place within the cell. Another important aspect of proteins is that most of the enzymes in the human body are proteins. Most of the intracellular reactions that take place are catalyzed by enzymes and hence proteins are central to the normal functioning of the cells. In the cell membrane certain proteins act as enzymes and they assist in carrying out react ions on the cell membrane surface. Proteins also act as cell adhesion molecules. These molecules possess the capability of attaching the cells to each other and also attaching the cell to the basal lamina. Proteins also have the ability to work as pumps for the passage of ions by the process of active transport which works against the normal diffusion gradient. They also act as carriers and work in moving substances by the process of facilitated diffusion which involves the movement of secondary substances in association with proteins for the purpose of transport. Another important role is as ion channels which only work upon stimulation and activation and allow the movement of ions in the intracellular or extracellular space. Glycoprotein’s present on the cell membrane also have functions related to the immune system. They function in the activities of the antibodies within the body and assist in recognizing the cells of the body from the foreign cells. Thus they protect the cells of the body from undergoing an autoimmune attack. The lipid bilayer of the cell membrane also plays an integral role in the selective permeability of the cell membrane. The bilayer is composed of phospholipids which are hydrophobic at one end and hydrophilic at one end (Guyton & Hall 2006; Ganong 2005). The question now arises as to how these two important molecules help in the selective permeability of the cell membrane. The lipid layer acts as a barrier for water soluble products such as glucose and urea whereas fat soluble substances can be moved through this lipid bilayer because of its properties. The steroid cholesterol plays an important role in maintaining the permeability of the cell membrane. Cholesterol has properties of lipids with a steroid nucleus and hence it only allows fat soluble products to pass through. It is through this lipid bilayer that the cell membrane gets the property of impermeability. The lipid bilayer of the cell membrane also does not allow the complex processes of active transport to occur through it. It only allows passive diffusion of certain substances inside the cell. One may ask as to how the cell survives without essential water soluble products of glucose when the lipid bilayer does not allow them to move inside the cell. The answer to this lies in the complexity of the protein molecules embedded in the cell membrane. It is for this purpose that specific carrier proteins have