Anatomy & Physiology

Anatomy & Physiology Study Guide of 368 chains of carbon atoms linked by covalent bonds. Familiar carbohydrates include the sugars and starches of a typical U.S. diet. Carbohydrates typically account for approximately one percent of total body weight. Although they may have other functions, carbohydrates are most important as energy sources that are catabolized rather than stored. There are three primary types of carbohydrates: monosaccharides, disaccharides, and polysaccharides. A monosaccharide, a simple sugar, is a carbohydrate containing three to seven carbon atoms. A monosaccharide can be called a triose (three-carbon), tetrose (four-carbon), pentose (five-carbon), hexose (six-carbon), or heptose (seven-carbon). The glucose, a hexose with the formula C6H12O6, is the most important metabolic “fuel” in the body. The atoms in a glucose molecule may form either a straight chain or a ring. In the body, the ring form is more common. Carbohydrates are generally complex molecules composed of monosaccharide building blocks. Two monosaccharides joined together form a disaccharide . Disaccharides, such as sucrose (table sugar), have a sweet taste. Of note, disaccharides and monosaccharides are quite soluble in water. Complex carbohydrates result from repeated dehydration synthesis reactions adding additional monosaccharides or disaccharides. These large molecules are called polysaccharides . Polysaccharide chains can be straight or highly branched. Starches are large polysaccharides formed from glucose molecules. Most starches are manufactured by plants. The digestive tract can break these molecules into monosaccharides. Starches, like potatoes and grains, are a major dietary energy source. 5.6 Lipids Lipids contain carbon, hydrogen, and oxygen, and the carbon-to-hydrogen ratio is typically near 1:2. However, lipids contain much less oxygen than carbohydrates with the same number of carbon atoms. Lipids may also possess small quantities of phosphorus, nitrogen, or sulfur. Familiar lipids include fats, oils, and waxes. Most lipids are insoluble in water, but special transport mechanisms carry them in the circulating blood. Lipids form essential structural components of all cells. In addition, lipid deposits are important as energy reserves. On average, lipids provide roughly twice as much energy as carbohydrates do, gram for gram, when broken down in the body. Lipids normally account for 12–18 percent of the total body weight of adult men, and 18–24 percent of the weight of adult women. Many kinds of lipids exist in the body, most notably, fatty acids, eicosanoids, glycerides, steroids, phospholipids, and glycolipids. 5.7 Proteins Proteins account for twenty percent of the total human body weight, making them the most abundant organic components. The human body contains many different proteins. Proteins are composed of carbon, oxygen, hydrogen, and nitrogen, and small quantities of sulfur and phosphorus in some. Proteins perform a variety of essential functions: building a framework for the body; providing cellular strength, organization, and support; facilitating muscular contraction; transporting ©2018 Achieve Page 54