Medical brain notes 27

  CHEMICAL REACTIONS A chemical reaction is a change brought about by the formation or breaking of chemical bonds. Two general types of reactions are synthesis reactions and decom-position reactions. In a  synthesis reaction , bonds are formed to join two or more atoms or molecules to make a new com-pound. The production of the protein hemoglobin in potential red blood cells is an example of a synthesis reaction. Proteins are synthesized by the bonding of many amino acids, their smaller subunits. Synthesis reactions require energy for the formation of bonds. In a  decomposition reaction , bonds are broken, and a large molecule is changed to two or more smaller ones. One example is the digestion of large molecules of starch into many smaller glucose mole-cules. Some decomposition reactions release energy; this is described in a later section on cell respiration.

  INORGANIC COMPOUNDS OF IMPORTANCE Inorganic compounds are usually simple molecules that often consist of only one or two different ele-ments. Despite their simplicity, however, some inor-ganic compounds are essential to normal structure and functioning of the body. WATER Water makes up 60% to 75% of the human body, and is essential to life for several reasons: 1.   Water is a  solvent ; that is, many substances (called   solutes) can dissolve in water. Nutrients such as glucose are dissolved in blood plasma (which is largely water) to be transported to cells throughout the body. The sense of taste depends upon the sol-vent ability of saliva; dissolved food stimulates the receptors in taste buds. The excretion of waste products is possible because they are dissolved in the water of urine.   2.   Water is a lubricant , which prevents friction where   surfaces meet and move. In the digestive tract, swallowing depends upon the presence of saliva, and muc...

  ORGANIC COMPOUNDS OF IMPORTANCE Organic compounds all contain covalently bonded carbon and hydrogen atoms and perhaps other ele-ments as well. In the human body there are four major groups of organic compounds: carbohydrates, lipids, proteins, and nucleic acids. CARBOHYDRATES A primary function of  carbohydrates  is to serve as sources of energy in cell respiration. All carbohydrates contain carbon, hydrogen, and oxygen and are classi-fied as monosaccharides, disaccharides, oligosaccha-rides, and polysaccharides.  Saccharide  means sugar, and the prefix indicates how many are present. LIPIDS Lipids  contain the elements carbon, hydrogen, and   oxygen; some also contain phosphorus. In this group of organic compounds are different types of sub-stances with very different functions. We will con-sider three types: true fats, phospholipids, and steroids (Fig. 2–7). True fats  (also called neutral fats) are made of one   molecule of glycerol and ...

  ORGANIC COMPOUNDS OF IMPORTANCE Organic compounds all contain covalently bonded carbon and hydrogen atoms and perhaps other ele-ments as well. In the human body there are four major groups of organic compounds: carbohydrates, lipids, proteins, and nucleic acids. CARBOHYDRATES A primary function of  carbohydrates  is to serve as sources of energy in cell respiration. All carbohydrates contain carbon, hydrogen, and oxygen and are classi-fied as monosaccharides, disaccharides, oligosaccha-rides, and polysaccharides.  Saccharide  means sugar, and the prefix indicates how many are present.   Monosaccharides,  or single-sugar compounds,   are the simplest sugars. Glucose is a  hexose , or six-carbon, sugar with the formula C 6 H 12 O 6  (Fig. 2–6). Fructose and galactose also have the same formula,  but the physical arrangement of the carbon, hydrogen, and oxygen atoms in each differs from that of glu-cose. This gives each hexose sugar ...