Physiology

Topics: Neuron, Signal transduction, Hormone Pages: 32 (8140 words) Published: June 18, 2013
1.3 Explain the structure of a cell membrane. Justify the functions of the cell membrane with its structure. In 1972, J.J Singer and G.L Nicolson has proposed a model to explain about the cell membrane known as Fluid Mosaic model. They are suggested that cell membrane is a dynamic structure composed of proteins and phospholipids. A cell membrane is the structure that completely encloses every cells and it can control the exchangement of substances such as nutrients and waste products . The plasma membrane is consists of combination of lipids, proteins and their derivatives. The phospholipid bilayer is the most fundamental structure of the plasma membrane. Other lipids, proteins and other components can be seen inside or the outside of the plasma membrane. Proteins embedded within the plasma membrane. The phospholipid bilayer

Phospholipid means fats that containing a phosphorous at one end of each molecule. There are two regions of phospholipid structure. Each phospholipid has a hydrophobic head that is attracted to water and hydrophobic tail repels water.

These phospholipids spontaneously arrange themselves into two layers like a sandwich. Their fatty acids arrange to the interior of the membrane and their head can be seen outer and inner surface of cells. In the plasma membrane , four major phospholipids can be found. They are,

Phosphatidylcholine
phosphotidylethanolamine
phosphotidylserine
spingomyelin
But all these phospholipid are not distributed in same way. It means, the outer surface of the plasma membrane consists of phosphotidylcholine and spingomyelin. The inner surface of the plasma membrane consists of phosphotidylethanolamine and phosphotidylserine. There is another class of phospholipid known as phophotidylinositol which is situated to the inner half of the plasma membrane.

In addition to these phospholipids, there are two types of lipids. They are glycolipids and cholesterol. Glycolipids are the lipids, containing carbohydrate chains. These glycolipids can be found in the outer leaflet of the plasma membrane. The carbohydrate portions of these glycolipids are localized on the cell surface.

Cholesterol is the another type of lipid in the plasma membrane. Cholesterol can be found in between the phospholipid bilayer. It can be found only in plasma membarane. Membrane proteins
There are two types of proteins. They are peripheral and integral membrane proteins. Integral proteins also known as Transmembrane proteins. Because they penetrate the lipid bilayer. They have hydrophobic regions and the hydrophiliv regions. Due to that regions these transmembrane proteins are considered as amphipatic. Peripheral membrane proteins can be associated with the surface of this bilayer. Furthermore, they are loosely bound to the surface of the peripheral proteins. They can be found in intracellular surface or the extracellular surface. Functions of the plasma membrane

The plasma membrane serves as the boundary between the cytoplasm of the cell and the external environment. It separates inside of the cell from outside of the cell. Function of the proteins.
Anything that enters or leaves the cell must pass the cell membrane. Plasma membrane control the entering substances and leaving substances. Some substances can move across the plasma membrane depending upon concentration gradient. It means substances can move from high concentration to lower concentration. This process doesn't need energy. Therefore this is referred as passive transport. 02, N2, Benzene, H2O, Urea, Glycerol, CO2 can pass through the plasma membrane easily.But some molecules cannot pass through the plasma membrane. It means some substances move across the membrane against to the concentration gradient. Those substances should move from lower concentration to high concentration. Therefore they need the energy for this process. Therefore this is referred as the active transport. ATP supplies the energy for this active...
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