Question

Compare and contrast the CELL MEMBRANE of gram-positive and gram-negative cells.Be sure to include function, structure, and characteristiques in your answer.

Answer 1

Cell membrane or cytoplasmic membrane is present immediately beneath the cell wall.

Structure: Approximately 7.5 nm thick and is composed of of phospholipids (about 20 - 30%) and proteins (60 - 70%). The phospholipid form a bilayer in which most of the proteins are tenaciously held (integral proteins). Other proteins are loosely attached (peripheral proteins). The lipid matrix of the membrane has fluidity, allowing the components to move around laterally. The phospholipids are phosphoglycerides, in which straight-chain fatty acids are ester-linked to glycerol.

Characteristics and function: The cytoplasmic membrane is a hydrophobic barrier to penetration by most water-soluble molecule. The cytoplasmic membrane also contains various enzymes involved in respiratory metabolism and in synthesis of capsular or cell-wall components. Because of its impermeability to protons (hydrogen ions), the cytoplasmic membrane is the site of genaration, of protonmotive force that is, the force that drives ATP synthesis, certain nutrient transport systems, and flagellar motility.

Gram negative bacteria contain an extra layer of cells called outer membrane or Lipopolsaccharide layer which surrounds the thin peptidoglycan layer, whereas Lipopolsaccharide layer is absent in Gram positive bacteria.

Spheroplasts: Gram negative bacteria with intact cytoplasmic membrane of the protoplast and the outer membrane (LPS layer) of the cell wall , after peptidoglycan layer is destroyed by lysozyme or its synthesis inhibited by antibiotics.

Protoplasts: Cells whose walls have been completely remove and are incapable of normal growth and division. These are prapared for gram positive bacteria by treating the cells with lysozyme which selectively dissolves cell wall.