Unit 2 (Plasma Membrane)

• It had been shown by Karl W. Nageli (1817-1891) that the cell membrane is semi- permeable and is responsible for the osmotic and other related phenomena exhibited by living cells.
• Plasma Membrane functions as semi-permeable or selectively permeable membrane.
• J.D. Robertson - "unit membrane concept"
• J.Q. Plowe - term the word plasmalemma
• Plasma membrane is primarily composed of protein and lipid, carbohydrates, and cholesterol.
• Lipids are fatty compounds that perform a variety of functions in our body.
• Cell membrane consist of 3 class of amphiphatic lipids: PHOSPHOLIPIDS, GLYCOLIPIDS, and CHOLESTEROLS
• PHOSPHOLIPIDS - consist of polar head and unsaturated fatty acid tails
• GLYCOLIPIDS - complex lipids comprising carbohydrates, fatty acid
• Cholesterol- composed of four fused carbons
• Carbohydrates - third major components of plasma membrane
• Proteins are the main component of plasma membrane. Second major component
• Membrane proteins are classified as or 2 main categories the integral (intrinsic) or peripheral (extrinsic) according to the degree of their association with the membrane
• Peripheral Proteins: They are also called extrinsic proteins associated with membrane surface.
• Integral or Intrinsic Proteins: These proteins penetrate the lipid layer wholly or partially and represent more than 70% of the two protein types.
• Danielli-Davson model (1934) suggested that the plasma membrane consists of two layers of lipid molecules.... phospholipid bilayer
• According to the view of Hiller and Hoffman (1953), plasma membrane consists of a mosaic of globular subunits or micelles.
• Garter and Grendel Model: founding fathers proposed in 1925
• Unit Membrane Model: proposed by J. David Robertson which aimed to explain all cellular structure of membrane
• Fluid Mosaic Model: Singer and Nicolson, 1972 - fluidity is important because it allows movement of integral proteins within the plane of the membrane
• The Fluid Mosaic Model suggests that the plasma membrane has an internal fluid phase consisting of phospholipids and cholesterol, and external hydrophilic regions where glycoproteins and glycolipids reside.