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1. Structure - Singer & Nicolson Fluid Mosaic Model
1. Lipids
1. Phosphoglycerides (amphipathic)
1. Glycerol (polar)
2. Fatty acid (non-polar)
2. Sterols - especially Cholesterol
2. Proteins - integral with annular lipids
1. Catalysis Enzyme
2. Recognition Receptor
3. Carrier-Mediated Transport
1. Facilitated Transport
1. In Aqueous Channel Membrane Channel
2. Bound to protein Transporter
2. Active Transport Pump
2. Function
1. Mechanisms of Crossing Membranes
1. Diffusion
1. From area of high concentration to area of low concentration
2. Rate of movement is proportional to difference in concentration (GRADIENT)
1. Non-saturation kinetics
3. Rate of movement is directly proportional to relative solubility in lipid & water
2. Carrier-mediated transport
1. Facilitated Diffusion
1. Via membrane Channel Protein
1. used more by ions than other substances
1. Na⁺, K⁺, Ca⁺⁺, Cl^-,
2. Variable specificity for the ions that will pass, size and charge
1. Basis for specificity is not well understood
2. Li⁺ will pass through some Na⁺ channels but K⁺, Rb⁺, & Cs⁺ will not
• These make and interesting comparison because they are all alkali metal cations.
3. Ions are surrounded by a layer of water molecules
3. Rate of movement proportional to gradient except at high concentrations
1. Exhibit saturation kinetics,
• at molar concentrations
• independent of temperature
2. Because pores become saturated or filled with substance
2. Via Transport Protein
1. Used by a wide variety of substances including ion
2. Very specific for substrate - form protein-substrate complex
3. Rate of movement proportional to gradient except at high concentrations
1. Exhibit Saturation Kinetics
• At micro-molar concentrations
• Highly dependent on temperature:
• 3 to 4 fold increase with 10 C increase in temperature
2. Exhibits Competitive Inhibition
4. Some will transport only one substance at the same time - uniporter
5. Some exhibit Coupled Transport
1. move two in same direction - symporter
2. move two in opposite directions - antiporter
2. Via Active Transport
1. Used by a variety of substances
2. Highly specific - form protein-substrate complex
3. Exhibit saturation Kinetics,
1. at micro-molar concentrations
2. temperature dependent
4. Exhibit competitive inhibition.
5. Direction of movement is opposite to diffusion
6. Consume energy
7. some exhibit coupled transport and some do not.

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