Summary
Highlights
Lipids are biomolecules like fats, oils, and steroids, characterized by their nonpolar nature, composed mainly of long hydrocarbon chains or ring systems. Unlike other polymers, they are generally not considered macromolecules.
TAGs are molecules with three ester groups, found in oils (liquid at room temperature) and fats (solid at room temperature). Upon hydrolysis, TAGs yield glycerol and three fatty acids. Fatty acids are carboxylic acids with long nonpolar hydrocarbon tails, which can be saturated (all single carbon-carbon bonds) or unsaturated (containing double bonds).
Saturated fatty acids have higher melting points due to their ability to pack neatly, maximizing van der Waals attractions. Unsaturated fatty acids, especially those with cis double bonds, have kinks that prevent orderly packing, resulting in lower melting points. Trans fats, often formed during partial hydrogenation, have linear shapes and higher melting points, making them difficult to metabolize and contributing to cardiovascular disease.
Lipids like TAGs are excellent for energy storage, releasing twice as much energy as carbohydrates due to numerous carbon-hydrogen bonds. They provide long-term energy, potentially sustaining a person for up to a month without food. An omega-3 fatty acid is defined by a double bond at the third carbon from the end of the chain.
Terpenes and terpenoids are another class of lipids. Terpenes are polymers of repeating 5-carbon isoprene units (e.g., myrcene, farnesene, limonene, beta-carotene). Terpenoids are similar but contain oxygen atoms (e.g., menthol). These compounds are found in various plants and fruits.
Deprotonated carboxyl groups of fatty acids form sodium salts, creating soap molecules with a polar head and a nonpolar tail. These form micelles in solution, encapsulating nonpolar dirt and grease, allowing them to be washed away by water. This explains why soap is essential for effective cleaning.