What is the fluid mosaic model?
The fluid mosaic model is a model conceived by S.J. Singer and Garth Nicolson in 1972 to describe the structural features of biological membranes. The membrane is described to be fluid because of its hydrophobic integral components such as lipids and membrane proteins that move laterally or sideways throughout the membrane. That means the membrane is not solid, but more like a 'fluid'. The membrane is depicted as mosaic because like a mosaic that is made up of many different parts the plasma membrane is composed of different kinds of macromolecules, such as integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol, lipoproteins. The structure of the cell membrane.
The cell membrane controls what enters and leaves the cell. The cell membrane is made up of 4 main components which are the phospholipid bilayer, membrane proteins, cholesterol and carbohydrates that are linked to some of the lipids. The phospholipid bilayer.
The phospholipid bilayer is made up of phospholipid molecules that arrange themselves into two rows hence giving the name bilayer.
The phospholipids are made up of two parts a phosphate and a lipid. Phosphates are hydrophilic, which means they are attracted to water. The phosphate repels fat and fat soluble materials find it difficult to pass through. Lipids are hydrophobic, which means they repel water. The phospholipid layer does not let many things pass into or out of the cell. This then leads to the question of how substances pass into and out of the cell. Within the phospholipid bilayer there are proteins embedded which enable other molecules to cross into or out of the cell. Cholesterol.
Cholesterol molecules are fitted in between the phospholipid bilayer molecules. The help to regulate the fluidity of the membrane and restrict movement of the phospholipids. Cholesterol also stops the membrane from breaking up. The cholesterol also reduces leakages of substances such as water through the membrane ensuring they pass through the correct channels.
There are four main types of proteins within the phospholipid bilayer. These are Channel proteins, transporter proteins, cell recognition proteins and receptor proteins. Channel proteins
Channel proteins let through any substances that are small such as salt and sugar
Each transporter protein is specific for one type of substance. A substance lands on the transporter protein and it flips to let things in and take things out of the cell
The receptor proteins act as receptors for specific chemicals such as hormones that trigger specific events within the cell.
Cell recognition protein
Cell recognition protein
Cell recognition proteins ensure that the cells are in the right place allowing cell to cell recognition. These are different for each person.
The proteins can be either intrinsic or extrinsic. Intrinsic proteins pass through the membrane and have a portion on the inside and outside of the cell. A channel protein is an intrinsic protein. Extrinsic proteins are fixed in one half of the phospholipid bilayer or attached to its surface. A receptor protein is an extrinsic protein.
The carbohydrates are linked to some of the lipids (this produces glycolipids) and proteins (Producing glycoproteins) on the non- cytoplasmic side of the membrane. These are important for cell to cell recognition