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Ultimate cell wall of 'Membrane Asymmetry'

 

 Introduction of Membrane Asymmetry

Asymmetry membrane lipid and protein molecules  which have an irregular distribution in monolayers of lipid and bilayer that are called membrane asymmetry.

A. Phospholipid asymmetry in the plasma membrane. 

The lipid composition of phospholipid and state of the fluidity of two halves of the lipid's bilayer are found to be strongly different in membrane asymmetry. For example, in human erythrocyte’s plasma membrane and asymmetry, the outer half contains those phospholipids which have more saturated fatty acid chains in membrane asymmetry, and the inner half contains in membrane those phospholipids which contain terminal amino groups and less saturated fatty acid chains. As a result, the inner monolayer is more fluid than the outer lipid monolayer. But some such phospholipid asymmetry is generated in smooth ER. The membrane asymmetry of glycolipids such as a galactocerebroside, ganglioside. etc., in the myelin sheath of nerves is found to be originated in human of Golgi apparatus in the lab. The specific rule of lipid asymmetry of the membrane is still not clear in membrane asymmetry.

B.  Protein asymmetry in the plasma membrane.

The outer sides of protein asymmetry and inner sides of the plasma membrane of asymmetry and other membranes do not present either the same and equal amounts of the various peripheral plasma membrane and integral proteins of membranes, For example, erythrocyte’s plasma membrane.

Proteins of the plasma membrane of erythrocytes. When the extracted proteins of the plasma membrane of human erythrocytes (RBC) are studies through SS polyacrylamide-gel electrophoresis, approximately 15 major protein bands are detected, varying in molecular weight from 15,000 to 25,000 which is plasma membrane is made up of cell.

 Important properties of some proteins are the following:

  • (i)    Spectrine and other cytoskeleton proteins of membrane asymmetry. Spectrin is the principal component of the protein meshwork that underline. Thus, it maintains the structural integrity and biconcave shape of membrane asymmetry, Spectrum is a long, thin, flexible rod about 100nm in length. It constitutes about 25% of the membrane asymmetry associated protein mass of membrane asymmetry. Spectrin is a heterodimer of membranes and consists of two non-identical membranes, antiparallel, loosely intertwined, flexible polypeptide chains, i.e., α-spectrin and β-spectrin, both being attached non-covalently to each other at multiple points including their ends in membrane asymmetry.
  • The spectrin heterodimers self-associate head to head to form 200nm long tetramers. The tail ends of 5 spectrin tetramers are linked to each other through binding to short actin filaments they are each with 15 actin monomers and to another protein that is called band 4.1 protein of cell membrane. These 3 types of proteins from the ‘junctional complex’ of a deformable, net-like meshwork of the cytoskeleton. Further, the binding of the spectrin cytoskeleton to the cytosolic face of the erythrocyte’s plasma membrane depends on a large intracellular attachment protein that is called ankyrin. Ankyrin tends to bind to both β- spectrin and to the cytoplasmic domain of a transmembrane protein that is called band 3 protein.
  • (ii)   Glycophorin. It is a small transmembrane of glycoprotein having a molecular weight of 55,000 daltons and 131 amino acid residues of glycophorin. This protein bears about 100 sugars on 16 separate oligosaccharide side chains of glycophorin. Despite there being more than 6 x 10⁵ glycophorin molecules per cell and their exact function is still not known it. However, glycophorins are found to contain certain antigenic determinants for the A, B, and O blood groups and MN blood groups. Further, sialic acid confers a high negative charge to the cell surface of erythrocytes of membranes. This sugar may be important in the life cycle of the erythrocytes as it has been shown that cells lose sialic acid as they age in the circulatory system of the cell. Correlated with this is the observation that loss of sialic acid is a signal for the removal of membrane asymmetry and destruction of an erythrocyte through the spleen and liver of the cell. In this way, the life span of red blood cells may be regulated in living being cells.
  • (iii)  Band 3 protein. Membrane asymmetry like that glycophorin's band 3 protein is a transmembrane of protein but it is a multi-pass membrane protein, i.e., it's highly folded in the polypeptide chain that extends across the lipid of bilayer at least 10 times of protein. Each human erythrocyte contains about 10⁶ and band 3 proteins, each of which forms either a dimer and tetramer in the cell membrane. Band 3 protein acts as the anion exchange channels in the cell membrane. As the erythrocytes pass through the lungs as well as they exchanges bicarbonate(HCO⁻) for chloride (Cl⁻) through these hydrophilic channels during the process of CO₂ release.

Constraints on the Motility of Membrane Molecules of a cell

In the fluid mosaic plasma membrane of constraints and it is not complete and independent freedom of movement for its different component molecules of membrane asymmetry. The mobility of living being lipid molecules is constrained since they remain tightly bound to the integral membrane proteins cell. For example, the mobility of lipid molecules surrounding cytochrome oxidase is immobilized through the enzyme and makes boundary lipid makes 30% of cell membrane lipid in the mitochondrial membrane of a living being.

The mobility and distribution of protein molecules are :

 (1) Certain proteins of the cell membrane are constrained through protein-protein interactions to form specialized ordered regions, representing 2 to 20 percent of the membrane of a system, for example, gap junctions, synapsis of neurons, and plaques of halobacteria of the cell.

 (2) Certain peripheral proteins (endoproteinase) of the cell which may form a bridge-like lattice work between integral proteins and restrict their lateral mobility of cell membrane, e.g., spectrin -ankyrin-actin cytoskeletal meshwork provides rigidity to the cell membrane of human  being erythrocyte and does not permit the clustering or capping of integral proteins when the appropriate antibodies or lectins are which is best for the membrane asymmetry. 

(3) In nucleated erythrocytic cells of membrane asymmetry, the mobility of the peripheral endoproteinase, and integral proteins are restrained by their attachment to the ectoplasmic cytoskeleton of the cell. The cytoskeleton is an extensive cell, including myosin filaments cell membrane, actin filaments, and microtubules. 

The human beings intercellular space of membrane asymmetry. In the tissues of multicellular animals and the plasma membranes of two adjacent cell membranes and it usually remains separated through a space of 10 to 150A° wide of plasma membrane asymmetry. This intercellular space is uniform and it contains material of low electron density which can be considered as a cementing substance of plasma membrane asymmetry. This substance is found to be a mucopolysaccharide in the living being cell membranes.

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