Chapter 3 - Carbohydrates and Lipids

Abstract

Carbohydrates (sugars) and lipids (fats) are the major sources of energy in our diet and are stored in our bodies primarily as glycogen in the liver and muscles and triglycerides in adipose tissue. Glucose (blood sugar) is the only sugar that exists in the body in free form; lactose and sucrose are important dietary disaccharides. Glycogen, starch, and cellulose are homoglucan polymers. Carbohydrates may be linked to proteins and lipids, forming glycoconjugates: glycoproteins and glycolipids. Fats (triacylglycerols, triglycerides) contain fatty acids esterified to glycerol. Fatty acids are long-chain alkanoic acids; unsaturated fatty acids contain one or more unconjugated cis-double bonds. Phospholipids are amphipathic glycerolipids containing a C-3 phosphodiester, linking a diglyceride to an amino compound - usually choline, ethanolamine, or serine. The fluid mosaic model describes the role of phospholipids, integral and membrane proteins, and other lipids in the structure and function of biological membranes. Biological membranes compartmentalize cellular functions and mediate ion and metabolite transport, signal transduction, and cellular interactions.