Lipids and membranes
Lipids and membranes | Biochemistry
Lipids
• Categories of compounds containing carbon, hydrogen, and oxygen.
• Heterogeneous class of naturally occurring organic compounds classified
together on the basis of common solubility properties:
o Insoluble in water, but soluble in organic solvents
o Amphipathic in nature
Classification of lipids
Lipids are classified according to their chemical structures in to 2 groups.
Classification 1
• Open chain forms
Consists of polar heads and non-polar, hydrophobic tails (fatty acids,
waxes, lipid-soluble vitamins, acylglycerols, eicosanoids, sphingolipids
phosphoacylglycerols)
• Cyclic forms
Consist of fused ring compounds (cholesterol and other steroids)
Classification 2
• Simple
o Acylglycerols
o Waxes
• Complex
o Phosphoacylglycerols (phospholipids)
o Sphingolipind
➢ Sphingomyelins(phospholipids)
➢ Glycolipids
Where are lipids derived from?
• Formed form C-atoms derived from fatty acids
o Cholesterol and other steroids
o Lipid-soluble vitamins
o Eicosanoids
, Lipids and membranes
Fatty acids
• Fatty acids are either components of lipid structures or are used for their
biosynthesis
• Carboxylic acids with long-chain hydrophobic side groups
• Long, unbranched chain carboxylic acids most commonly of 12 -20 carbons
(even numbers)
• Derived from hydrolysis of animal fats, vegetable oils, or phosphoacylglycerols
of biological membranes
• Typically contain a polar head, and a non-polar long carbon tail-amphipathic
• Amphipathic molecules aggregate into molecular arrangements called
micelles (spherical vesicles)
o The interior is hydrophobic and the exterior associates with water
Saturated fatty acids
o Fatty acids that contain only C-C are saturated
o Melting points increases with increase in number of C-atoms (stronger
hydrophobic interactions)
Table 1: Typically, Naturally Occurring Saturated Fatty acids
, Lipids and membranes
Common name: Lauric acid
Systematic name: Dodecanoic acid (saturated)
Above structure includes all the C and H atoms- unprotonated form of the acid
Zig-zag structures without C and H atoms
Unsaturated fatty acids
o Fatty acids that contain C=C are unsaturated
o Mono-unsaturated (one double bond), polyunsaturated (2 or more double
bonds)
o Melting points decreases with increases in number of double bonds
(unsaturation)
o Liquid at room temperature
o Vegetables fat: Polyunsaturated fatty acids > Saturated fatty acids
o Liquids
o Animal fats: Saturated fatty acids > Polyunsaturated fatty acids
o Solids
o In most unsaturated fatty acids, the cis isomer predominates, the trans
isomer is rare.
Lipids and membranes | Biochemistry
Lipids
• Categories of compounds containing carbon, hydrogen, and oxygen.
• Heterogeneous class of naturally occurring organic compounds classified
together on the basis of common solubility properties:
o Insoluble in water, but soluble in organic solvents
o Amphipathic in nature
Classification of lipids
Lipids are classified according to their chemical structures in to 2 groups.
Classification 1
• Open chain forms
Consists of polar heads and non-polar, hydrophobic tails (fatty acids,
waxes, lipid-soluble vitamins, acylglycerols, eicosanoids, sphingolipids
phosphoacylglycerols)
• Cyclic forms
Consist of fused ring compounds (cholesterol and other steroids)
Classification 2
• Simple
o Acylglycerols
o Waxes
• Complex
o Phosphoacylglycerols (phospholipids)
o Sphingolipind
➢ Sphingomyelins(phospholipids)
➢ Glycolipids
Where are lipids derived from?
• Formed form C-atoms derived from fatty acids
o Cholesterol and other steroids
o Lipid-soluble vitamins
o Eicosanoids
, Lipids and membranes
Fatty acids
• Fatty acids are either components of lipid structures or are used for their
biosynthesis
• Carboxylic acids with long-chain hydrophobic side groups
• Long, unbranched chain carboxylic acids most commonly of 12 -20 carbons
(even numbers)
• Derived from hydrolysis of animal fats, vegetable oils, or phosphoacylglycerols
of biological membranes
• Typically contain a polar head, and a non-polar long carbon tail-amphipathic
• Amphipathic molecules aggregate into molecular arrangements called
micelles (spherical vesicles)
o The interior is hydrophobic and the exterior associates with water
Saturated fatty acids
o Fatty acids that contain only C-C are saturated
o Melting points increases with increase in number of C-atoms (stronger
hydrophobic interactions)
Table 1: Typically, Naturally Occurring Saturated Fatty acids
, Lipids and membranes
Common name: Lauric acid
Systematic name: Dodecanoic acid (saturated)
Above structure includes all the C and H atoms- unprotonated form of the acid
Zig-zag structures without C and H atoms
Unsaturated fatty acids
o Fatty acids that contain C=C are unsaturated
o Mono-unsaturated (one double bond), polyunsaturated (2 or more double
bonds)
o Melting points decreases with increases in number of double bonds
(unsaturation)
o Liquid at room temperature
o Vegetables fat: Polyunsaturated fatty acids > Saturated fatty acids
o Liquids
o Animal fats: Saturated fatty acids > Polyunsaturated fatty acids
o Solids
o In most unsaturated fatty acids, the cis isomer predominates, the trans
isomer is rare.
