lipids: membrane structure - wou homepagewou.edu/~guralnl/451introlipids.pdfchain • double bonds...
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Lipids: Membrane Structure
• Role of lipids• Fatty acid structure
and nomenclature• Types of membrane
lipids• Structure of
membrane• Membrane fluidity
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Role of lipids
• Energy• Energy Storage• Hormones• Vitamins• Digestion• Insulation• Membrane structure: Hydrophobic
properties
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Lipids
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Fatty acid nomenclature
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Fatty acid Structure
• Long hydrocarbon chains
• Various lengths• Saturated Fatty acids• No double bond
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Unsaturated Fatty acids• One or more double
bonds• Cis: cis-∆9, double
bond between 9 and 10 carbon
• Trans: trans- ∆2, double bond between 2 and 3 carbon
• ω-3 counting from the distal end.
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Types of membrane lipids
• Phospholipids• Glycolipids• Cholesterol
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Phospholipids
• Glycerol backbone• 2 fatty acids usually
one saturated and one unsaturated
• C-3 carbon has phosphoric acid group
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Types of phospholipids
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Sphingomyelin: amino alcohol
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Glycolipids: sugar containing lipids
• Cerbroside• Gangliosides:
branched chain of sugars
• Extracellular side of membrane
• receptors
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Cholesterol
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Structure of membrane
• Membrane bilayer• Lipids are amphipathic:
hydrophillic and hydrophobic
• Contains phospholipids, glycolipids, cholesterol, and proteins
• Membranes are asymmetric
• Membranes are fluid• Proteins mediate most
functions
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Membrane bilayer
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Lipid bilayers• Nanometers to millimeters in thickness, usually 6-10 nm• Self assembly: entropy• Impermeable to ions and most polar molecules to form
boundaries• Create a charge difference
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Membrane proteins
• Protein ratio in membranes can vary from 1:4 to 4:1 depending on function
• Integral proteins• Peripheral proteins
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Membrane fluidity
• Phospholipids can diffuse laterally
• Rotations from one face to the other is very slow
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Control of membrane fluidity
• Processes require some fluidity• Tm = melting temperature depends on length of fatty acid
chain• Double bonds increase fluidity• Cholesterol inserts into bilayers and disrupts
interactions; moderates fluidity
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Fatty acid composition• Bacteria can vary number of double bonds to
regulate fluidity• Eukaryotic cells (and bacteria) can change fatty
acid composition with ratio of saturated to unsaturated fatty acids and chain length