Membranes: Their Structure, Function, and Chemistry

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Chapter 7 Membranes Their Structure, Function,
and Chemistry
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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
• Phospholipids
• Glycolipids
• 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
• Phospholipids
• Glycolipids
• 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
• Phospholipids
• Glycolipids
• 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
• Integral
• Peripheral
• Lipid anchored

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1. Integral Membrane Proteins

• Have hydrophobic and hydrophilic regions
• Two types
• Monotropic
• 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
• Integral
• Peripheral
• Lipid anchored

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2. Peripheral Membrane Proteins
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Membrane Proteins

• Classes of membrane proteins
• Integral
• Peripheral
• 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