Fluid-Mosaic Model of Plasma Membrane
1. Phospholipids: There are five types of phospholipids in the cell membrane. Lecithin, cephalin, glycolipid, glycophosphotide and phosphotidic acid. Phospholipids are arranged in two layers. Each layer is composed of numerous lipid molecules. Each lipid molecule has two parts. head and tail The large outer part is called the head. It is spherical or oval and composed of phosphates. It is polar and hydrophilic. The two filament-like parts attached to the head are called tails. It is composed of fatty acids. The tail is non-polar and hydrophobic. Between the head and the tail is the gyserol. Lipid molecules are always moving, shaking and bouncing around each other. This type of movement is called flip flop movement. As the layers move between the two layers due to frictional motion, the membrane feels like a fluid.
2. Proteins: There are three types of proteins in the plasma membrane. These are-
(i) Peripheral Protein: The protein which is located at the edge of the lipid layer is called peripheral protein. It looks round. It is enzyme in nature. It remains attached to the cytoskeleton. Cyclins are produced from abundant pollen grains by the action of membrane bound enzymes.
(ii) Intrinsic Protein: The protein that is in the intrinsic state inside the lipid layer is called intrinsic protein. It looks oval. Acts as a carrier and transports essential substances. It maintains cell-to-cell adhesion.
(iii) Intermembrane Protein: The protein that extends from one end of the lipid layer to the other end is called an intermembrane protein. It is the largest protein. It changes its structure by taking energy from the ancha. As a result, a hole is created through it. Essential substances move through these pores. It acts as a receptor for hormones, neurotransmitters, mediated endocytosis, insulin etc. Various molecules, ions and electrons move through channels, pumps and electron transport chains.
3. Glycocalyx (Carbohydrate): Carbohydrate chains are present on the outside of the cell membrane. Carbohydrate chains are attached to lipids to form glycolipids and proteins to form glycoproteins. Glycoproteins and glycolipids together are called glycocalyx or cell coat. It acts as a cell-marking factor. It helps in the movement of essential substances.
4. Cholesterol: Cholesterol is a type of steroid. It has a claw on its head and is water absorbent. The other part is water repellent. Cholesterol is sandwiched between phospholipid molecules. It is irregularly arranged. Cholesterol is higher in animal cells and lower in plant cells.
Protein molecules are scattered between phospholipids in the cell membrane. Because of this, the protein molecules look like a mosaic when viewed from the surface of the cell membrane. To explain this situation in one word, the cell membrane model has been named ‘Fluid Mosaic Model’.