chemical composition of plasma membrane

INTRODUCTION
plasma membrane is also known as cell membrane or cytoplasm membrane.
It is the biological membrane, separates interior of the cell from the outside environment.
Selective permeable to Ions and organic molecules.
Its basic function is to protect the cell from its surroundings.
It consists of the phospholipids bilayer with embedded proteins.
Cell membranes are involved in:�cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for several extracellular structures.

1. PREPARED BY: BASHARAT NAUMAN REG# 5537 MICROBIOLOGY 3 RD STR ABASYN UNIVERSITY PESHAWAR

2. CHEMICAL COMPOSITION OF PLASMA MEMBRANE Introduction Chemical composition Molecular structure Membrane lipids Membrane proteins Membrane carbohydrates Structural organization of cell membrane

3. INTRODUCTION plasma membrane is also known as cell membrane or cytoplasm membrane. It is the biological membrane, separates interior of the cell from the outside environment. Selective permeable to Ions and organic molecules. Its basic function is to protect the cell from its surroundings. It consists of the phospholipids bilayer with embedded proteins. Cell membranes are involved in: cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for several extracellular structures.

4. Chemical   composition: Cell membranes contain a variety of biological molecules, notably lipids and proteins. Some of the proteins and lipids, however, may have oligosaccharides, covalently attached to them. The sugar containing sequences of these glycoprotein and glycolipids also play a role in determining the identity of cells.

5. Molecular   structure: The molecular structure of cell membrane id totally dependent on: Membrane   Lipids Membrane   Proteins Membrane   Carbohydrate

6. Membrane lipids The cell membrane consists of three classes of amphipathic lipids:  phospholipids , glycolipids, and sterols. The fatty chains in phospholipids and glycolipids usually contain an even number of carbon atoms, typically between 16 and 20. The entire membrane is held together via non-covalent interaction of hydrophobic tails. In animal cells cholesterol is normally found in the irregular spaces between the hydrophobic tails of the membrane lipids, where it confers a stiffening and strengthening effect on the membrane. The major lipids in the cell membrane is phospholipids.

7. Phospholipids molecule

8. Continued…. Each phospholipid molecule has hydrophilic (polar) head and a hydrophobic (non-polar) tail. The hydrophilic heads interact with water while hydrophobic tails remain away from it and in contact with each other. hydrophilic and hydrophobic molecules interact differently with water.  hydrophilic molecules dissolve readily in water because they contain charged groups or uncharged polar groups that can form either favorable electrostatic interactions or hydrogen bonds with water molecules.  Hydrophobic molecules, by contrast, are insoluble in water because almost all, of their atoms are uncharged and nonpolar and therefore cannot form energetically favorable interactions with water molecules.

9. Continue… For that reason, lipid molecules spontaneously aggregate to bury their hydrophobic tails in the interior and expose their hydrophilic heads to water. The lipid molecules exchange positions horizontally (laterally) with their neighbours in the same layer.  In this energetically most-favorable arrangement, the hydrophilic heads face the water at each surface of the bilayer, and the hydrophobic tails are shielded from the water in the interior.

10. Membrane   Proteins The cell membrane has large content of proteins, typically around 50% of membrane volume. large variety of protein receptors and identification proteins, such as antigens, are present on the surface of the membrane. Functions of membrane proteins can also include cell–cell contact, surface recognition, cytoskeleton contact, signaling, enzymatic activity, or transporting substances across the membrane.

11. Continue… There are three types of proteins in plasma membrane. Integral proteins, Transmembrane proteins and Peripheral proteins.

12. Integral proteins are usually globular and they normally extend in the interior of the lipid bilayer. It directly interacts with hydrophobic regions of the bilayer. The hydrophilic regions of integral proteins are generally exposed to the cytoplasm and external aqueous phase outside the cell. They carry out all the functions of the membrane such as transport of molecules across the membrane, receiving signals from hormones and establishing cell shape. Transmembrane proteins are also integral proteins.

13. Transmembrane protein is a type of integral protein spanning the entirety of the biological membrane to which it is permanently attached. transmembrane proteins span from one side of a membrane through to the other side of the membrane. Many transmembrane proteins function as gateways to deny or permit the transport of specific substances across the biological membrane, to get in or out of the cell as in the case of waste byproducts.

14. Peripheral membrane proteins  are proteins that adhere only temporarily to the biological membrane with which they are associated. These molecules attach to integral membrane proteins, or penetrate the peripheral regions of the  lipid bilayer . The reversible attachment of proteins to biological membranes has shown to regulate cell signaling and many other important cellular events. Membrane binding may promote rearrangement, dissociation, or conformational changes within many protein structural domains, resulting in an activation of their biological activity.

15. Membrane Carbohydrate Carbohydrates ( oligosccharides ) in plasma membrane occur as glycol proteins and glycolipids most of the membrane carbohydrates are bound to protein molecules. Carbohydrate chains of all the cell membranes are located extensively on the exoplasmic surface, i.e. outside the cell. Although the functions of membrane carbohydrates are yet to be established, they seem to be involved in cell communication and recognition processes.

16. Structural organisation of plasma   membrane:    the mid 19th century, Moritz Traube noted that the outer layer of cell is semi permeable to allow transport of ions. Traube had no direct evidence for the composition of this film, though, and incorrectly asserted that it was formed by an interfacial reaction of the cell protoplasm with the extracellular fluid. The fatty and oily nature of the cell membrane was first correctly intuited by Quincke , who noted that a cell generally forms a spherical shape in water and, when broken in half, forms two smaller spheres. In 1902 Hans Meyer and Ernest Overton proposed that the plasma membrane is composed of a thin layer lipid molecule. James Danielli and Hugh Davson in 1935 proposed the lipid bilayer model.

17. Continue… In early 1960, David Robertson proposed that, plasma membrane was of uniform thick with two protein (outer and inner) coats and middle phospholipid bi-layer. John Singer and Garth Nicolson modified David’s model and called it fluid mosaic.

18. FLUID MOSAIC MODEL

19. Continued… John Singer and Garth Nicolson proposed the fluid mosic model of the plasma membrane. According to this model biological membranes can be considered as a two-dimensional liquid in which lipid and protein molecules diffuse more or less easily. Although the lipid bilayers that form the basis of the membranes do indeed form two-dimensional liquids by themselves, the plasma membrane also contains a large quantity of proteins, which provide more structure. Examples of such structures are protein-protein complexes, pickets and fences formed by the actin -based  cytoskeleton , and potentially  lipid rafts .

20. references www.wikipedia.org/introduction,chemical ... www.mville.digication.com www.profosinubi.com