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Index >> Cellular Components >> Cytoplasmic Membrane

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Biosynthesis of Cellular Components Biosynthesis of Capsular Materials Peptidoglycan Biosynthesis Antibiotics Affecting Cell Wall Synthesis Teichoic Acid Gram Negative Bacterial Cell Envelope Cytoplasmic Membrane Informational Macromolecules Deoxyribonucleic Acid (DNA) Ribonucleic Acid (RNA) Properties of RNA

Cytoplasmic Membrane

	Cytoplasmic Membrane - The cytoplasmic membrane consists of a phosphor lipid bilayer with proteins. The phosphor lipids are so arranged that the hydrophilic heads are exposed to aqueous medium on both sides of the membrane. Each monolayer is a two dimensional fluid. The lipid molecules can diffuse laterally as in a liquid film but can rarely execute a flip-flop transition from one layer to the other. Because the lipid bilayer is a two dimensional fluid, any protein molecule embedded in it can also diffuse laterally. Proteins associated with membranes fall into two classes: (i) integral membrane proteins which are those with a portion of each molecule embedded in the lipid bilayer.
These proteins have been found to span the full width of the bilayer and so have regions exposed on both sides of the membrane, (ii) peripheral membrane proteins which are not inserted into the bilayer but reside at one surface or the other. Each peripheral protein molecule is bound to an integral protein Membranes grow only by expansion and they cannot be broken open for the insertion of new material. The lipids are synthesized within the membrane. The major constituents are phosphatidyle thanolamine and phosphatidylserine.
The synthesis of phosphatidyle thanolamine which is the major phosphor lipid in E.coli, begins with two molecule of a fatty acid which are transferred from a donor to a molecule of glycerol phosphate to form phosphatidic acid. In a subsequent step, CMP is attached to phosphatidic acid and later on replaced by serine. The decarboxylation of serine leads to the production of phosphatidylethanolamine The synthesis and assembly of the membrane proteins is a coupled process. A leader region consisting of 20 amino acids in the nascent polypeptide helps the growing polypeptide to insert into the membrane and allows the movement of the peptide outwards. The polypeptide does not completely pass through the membrane and get attached there. Once the protein has folded it cannot be pulled out of the membrane nor can it execute a flip-flop movement but is anchored in an asymmetric orientation.

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DNA Replication Enzymology of DNA Replication Properties of E.Coli DNA Polymerases Biosynthesis of RNA Transcription Proteins Protein Structure Protein Synthesis Amino Acids Genetic Code Breaking the Genetic Code List of Genetic Code

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