Biochemistry of Lipids Lecture 1

Lipids

• Lipids are hydrophobic, nonpolar molecules, soluble in nonpolar solvents and insoluble in polar solvents like water.

Fatty Acids

• Fatty acids belong to the carboxylic acid family and contain a carboxylic acid group, making them polar.
• They also have a long hydrocarbon tail, making them nonpolar overall.
• Fatty acids typically contain between 12 and 20 carbon atoms, usually an even number.
• Fatty acids with no carbon-carbon double bonds are saturated, while those with double bonds are unsaturated, and those with multiple sites of unsaturation are polyunsaturated (PUFAs).

Properties of Fatty Acids

• Melting points of saturated fatty acids increase with the number of carbon atoms.
• Unsaturation lowers the melting points of fatty acids due to the cis configuration of double bonds.
• The common fatty acids found in biological systems are shown in Table 8.1 of Raymond.

Essential Fatty Acids

• Essential fatty acids (EFAs) are unsaturated fatty acids that cannot be synthesized by the body and must be supplied in the diet.
• Examples of EFAs include linoleic acid, linolenic acid, and arachidonic acid.

Representation of Fatty Acids

• The shorthand representation of fatty acids includes the total number of carbon atoms, the number of double bonds, and the position of double bonds, starting from the carboxyl end.
• Examples of shorthand representation include palmitic acid (16:0), oleic acid (18:1:9), and arachidonic acid (20:4;5,8,11,14).

Delta System

• The site of unsaturation in a fatty acid is indicated by the symbol Δ and the number of the first carbon of the double bond relative to the carboxylic acid group (–COOH).
• Example: palmitoleic acid is designated as 16:1Δ9, indicating a 16-carbon fatty acid with one site of unsaturation between carbons 9 and 10.

Function of Lipids

• Lipids are a source of high energy value (1 gram = 9 calories).
• Lipids are constituents of membrane structure and regulate membrane permeability.
• Lipids serve as a source of fat-soluble vitamins (A, D, K, and E).
• Lipids are important as cellular metabolic regulators (steroid hormones and prostaglandins).
• Lipids (phospholipids) participate in the electron transport chain in the inner mitochondrial membranes.

This quiz covers the introduction to lipids, their characteristics, and types including fatty acids, triglycerides, steroids, and eicosanoids.