BIOL 2020 Lecture Notes - Lecture 3: Cell Membrane, Phospholipid, Hydrophile
The Structure and Function of the Plasma Membrane
September 16, 2015
Reading Assignment: Pg. 120-147
Membrane Functions:
• Compartmentalization (bounded by membranes) – keeps conflicting activities seperate
• Scaffold for biochemical activities
• Provides a selectively permeable barrier
• Allows transport of solutes (dissolved in water)
• Responds to external signals in a very specific manner
• Intercellular interaction (cells interact with one another through membranes)
• Energy transduction – conversion of energy from one form to another
Membrane Composition:
• Lipids – bimolecular layer (gives selective permeability-not water soluble)
o Amphipathic: hydrophilic and hydrophobic
o Form phospholipids
• Proteins – do the work of the membrane
• Carbohydrates -
Phospholipid:
*AMPHIPATIC
Cholesterol – Amphipathic
• Can be up to 50% of a membrane
• A significant portion of phospholipids
• Useful for membrane assembly
Membrane Lipid Bilayer: water – head groups – fatty acid chains – head groups – water
• Backbone structure
The membrane is extremely fluid in nature and flexible so lipids have a rotational and lateral
diffusion in the membrane. Lipids will not normally flip over to the over side of the bilayer. *Very
rare without proteins present (not spontaneous).
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Document Summary
The structure and function of the plasma membrane. *amphipatic: can be up to 50% of a membrane, a significant portion of phospholipids, useful for membrane assembly. Membrane lipid bilayer: water head groups fatty acid chains head groups water: backbone structure. The membrane is extremely fluid in nature and flexible so lipids have a rotational and lateral diffusion in the membrane. Lipids will not normally flip over to the over side of the bilayer. Lipid bilayers will seal together spontaneously due to hydrophobic properties. In organelles, faces away from cytosol as well. *both lipids and proteins rotate = rotational diffusion. Some proteins remove randomly and are very slow, some suggesting that it is interacting with something on the other side of the membrane. Some proteins may be contained in a network until it can move freely. Other proteins seem to be immobile but attaches to structures outside of the cell.
