TAILIEUCHUNG - Lecture Biology - Chapter 5: Membrane structure and function

Chapter 5 - Membrane structure and function, after studying this chapter, you should be able to accomplish the following outcomes: Describe the structure of the plasma membrane and the diverse functions of the embedded proteins; describe what is meant by a semipermeable membrane; predict the effect of osmotic conditions on animal versus plant cells;. | Membrane Structure and Function Chapter 5 Membrane Structure The fluid mosaic model of membrane structure contends that membranes consist of: -phospholipids arranged in a bilayer -globular proteins inserted in the lipid bilayer Membrane Structure Cellular membranes have 4 components: 1. phospholipid bilayer 2. transmembrane proteins 3. interior protein network 4. cell surface markers Membrane Structure Membrane structure is visible using an electron microscope. Transmission electron microscopes (TEM) can show the 2 layers of a membrane. Freeze-fracturing techniques separate the layers and reveal membrane proteins. Phospholipids Phospholipid structure consists of -glycerol – a 3-carbon polyalcohol acting as a backbone for the phospholipid -2 fatty acids attached to the glycerol -phosphate group attached to the glycerol Phospholipids The fatty acids are nonpolar chains of carbon and hydrogen. -Their nonpolar nature makes them hydrophobic (“water-fearing”). The phosphate group is polar and hydrophilic (“water-loving”). Phospholipids The partially hydrophilic, partially hydrophobic phospholipid spontaneously forms a bilayer: -fatty acids are on the inside -phosphate groups are on both surfaces of the bilayer Phospholipids Phospholipid bilayers are fluid. -hydrogen bonding of water holds the 2 layers together -individual phospholipids and unanchored proteins can move through the membrane -saturated fatty acids make the membrane less fluid than unsaturated fatty acids -warm temperatures make the membrane more fluid than cold temperatures Phospholipids Membrane Proteins Membrane proteins have various functions: 1. transporters 2. enzymes 3. cell surface receptors 4. cell surface identity markers 5. cell-to-cell adhesion proteins 6. attachments to the cytoskeleton Membrane Proteins Peripheral membrane proteins -anchored to a phospholipid in one layer of the membrane -possess nonpolar regions that are inserted

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