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Fatty Acids and Glycerol
Fatty acids and glycerol molecules are the building blocks of lipids. Fatty acids have a carboxyl group (-COOH) that is attached to long chains of carbon and hydrogen atoms. These chains are also called hydrocarbon tails and vary in length and number of carbon atoms. The hydrocarbon tails are hydrophobic and are not soluble in water. Glycerol is a three-carbon chain where each carbon has a hydroxyl group (-OH) attached to it. Glycerol is able to bond with fatty acids and so, together, these two molecules form lipids.
Structure
To form larger lipids, fatty acids and glycerol are linked together using ester bonds which are a type of covalent bond. Differences in saturation determine the structure and function of lipids. Saturation is a description of how straight or bent the fatty acids of a lipid are. Fatty acids that have more double bonds in their hydrocarbon chain produce more unsaturated lipids since the chain is kinked and the lipids do not fit as tightly together. On the other hand, fatty acids that have only single bonds in their hydrocarbon chain produce more saturated lipids since the chain is straighter. Examples of lipids are triglycerides, phospholipids, and cholesterol.
Function
Lipids are nonpolar, hydrophobic macromolecules that are primarily involved in energy storage, membrane structure, and cell signaling. Triglycerides are used for long-term energy storage. While carbohydrates also store energy, triglycerides are able to store more energy per gram. Phospholipids, which we will discuss more when we learn about cell membranes, consist of two fatty acid chains, a phosphate group, and a glycerol molecule. These molecules have a polar region that is able to interact with water and a nonpolar region that is very hydrophobic. Steroids are another kind of lipid that have a four-ring structure and are precursors to hormones and other signaling molecules.
