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Slide 1
Chapter 7:
Membranes: Their
Structure, Function, and
Chemistry
Slide 2
Membrane Functions
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The Fluid-Mosaic Model
• First proposed in 1972 by Singer and Nicolson
• Lipids: The “fluid” portion
• Proteins: The “mosaic” portion
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Membrane Lipids
• Three major classes of lipids found in membranes
1. Phospholipids
2. Glycolipids
3. Sterols
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Phospholipids
• The most abundant membrane lipid
• Glycerol based vs. Sphingosine based
• Type and portion varies with membrane source
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Glycerol vs. Sphingosine
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Phospholipids (cont.)
• The most abundant membrane lipid
• Glycerol based vs. Sphingosine based
• Type and portion varies with membrane source
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Phospholipid Composition of
Membranes
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Membrane Lipids (cont.)
• Three major classes of lipids found in membranes
1. Phospholipids
2. Glycolipids
3. Sterols
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Glycolipids
• Carbohydrate attached to a lipid
• Some are glycerol based, but most are
sphingosine based
• Glycosphingolipids
• Cerebrosides
• Gangliosides
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Glycolipids (cont.)
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Membrane Lipids (cont.)
• Three major classes of lipids found in membranes
1. Phospholipids
2. Glycolipids
3. Sterols
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Sterols
Several types of sterols found in membranes:
• Cholesterol
• Phytosterol
• Ergosterol
• Sterols absent from some membranes
• Hopanoids
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Sterols (cont)
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Fatty Acids
• Component of all membrane lipids (except
cholesterol
• Essential to membranes because of hydrocarbon
chains
• Presence of double bonds alters structure
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Fatty Acids (cont.)
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Membrane Asymmetry
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Membrane Fluidity
• Lateral movements of proteins and lipids is
common
• Lipids move rapidly
• Proteins move slower
• Necessary for proper membrane function
• Tm = transition temperature
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Factors Membrane Fluidity
• Length of fatty acid chains
• Amount of fatty acid saturation
• Number of sterols
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Fatty Acids and Membrane Fluidity
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Fatty Acids and Membrane Fluidity cont
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Factors Membrane Fluidity (cont)
• Length of fatty acid chains
• Amount of fatty acid saturation
• Number of sterols
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Sterols and Membrane Fluidity
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Regulation of Membrane Fluidity
Why important?
• Membranes would “gel” at lower temperatures
• Increased fluidity at higher temperatures makes it
difficult to maintain ion concentration
Homeoviscous adaptation
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Lipid Rafts
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The Fluid-Mosaic Model (again)
• First proposed in 1972 by Singer and Nicolson
• Lipids: The “fluid” portion
• Proteins: The “mosaic” portion
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Membrane Proteins
Classes of membrane proteins:
1. Integral
2. Peripheral
3. Lipid anchored
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1. Integral Membrane Proteins
• Have hydrophobic and hydrophilic regions
• Two types:
1. Monotropic
2. Transmembrane
- Single pass
- Multi pass
- Multi-subunit
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1. Integral Membrane Proteins (cont.)
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Membrane Proteins
Classes of membrane proteins:
1. Integral
2. Peripheral
3. Lipid anchored
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2. Peripheral Membrane Proteins
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Membrane Proteins
Classes of membrane proteins:
1. Integral
2. Peripheral
3. Lipid anchored
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3. Lipid Anchored Membrane Proteins
• Covalently bound to lipids in the membrane
bilayer
• Interior
• Bound to fatty acid
• Bound to isoprenyl
• Exterior
• Bound to glycosylphosphatidlinositol (GPI)
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3. Lipid Anchored Membrane Proteins
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Glycosylation
• Process of adding a carbohydrate side chain to a
protein
• N – linked vs O – linked
• Carbohydrate chains branched and vary in
length and composition
• Carbohydrate chains generally on exterior of cell
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N – Linked vs.
O – Linked
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Glycosylation
• Process of adding a carbohydrate side chain to a
protein
• N – linked vs O – linked
• Carbohydrate chains branched and vary in
length and composition
• Carbohydrate chains generally on exterior of cell
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Glycosylation
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Glycosylation
• Process of adding a carbohydrate side chain to a
protein
• N – linked vs O – linked
• Carbohydrate chains branched and vary in
length and composition
• Carbohydrate chains generally on exterior of cell