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Lecture 2

2012.02.11 - Bio 1202 Lecture 2 Review Notes.docx

2 Pages

Course Code
Biology 1202B
Gardiner/ Murphy

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Lecture 2  Cell membranes – all cells have them o The proteins in the plasma membrane may provide a variety of major cell functions  For example: transport, enzymic activity, cell-cell recognition, intercellular joining  Freeze-Fracture Method – freeze cells and hit them with a chisel near the middle to study them  S.J. Singer and G. Nicolson (1972) – made a model that proposed the membrane proteins are dispersed and individually inserted into the phospholipid bilayer o This model was called the fluid mosaic model  The hydrophilic regions of proteins and phospholipids are in maximum contact with water and the hydrophobic regions are in a nonaqueous environment  Phospholipids: hydrophobic tails and hydrophilic heads  Membranes are fluid – must be to function o Membrane molecules are held in place by relatively weak hydrophobic interactions o Most of the lipids and some proteins can drift laterally in the plane of the membrane (but they rarely flip-flop from one layer to the other)  These lateral movements are rapid o Fluidity is influenced by temperature and by its contents  Cold – membranes switch from fluid to solid state (phospholipids more closely packed)  Membranes rich in unsaturated fatty acids are more fluid than saturated o Amount of cholesterol may vary on the membrane  Plasma – one cholesterol per phospholipid molecules  Other membranes (like those around bacteria) have no cholesterol o Membranes are approx. 8nm thick  Proteins – determine most of the membrane’s specific functions o Peripheral proteins – not embedded in the lipid bilayer  Loosely bound to the surface o Integral proteins – imbedded in the core of the lipid bilayer o Trans-membrane proteins – start from one side of the membrane, and continue to the other o These proteins reinforce the shape of the cell and provide a strong framework  The membrane plays a key role in cell-cell recognition (the ability of a cell to distinguish one type of neighbouring cell f
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