coded in genes cells use their molecular machinery machinery to build the proteins required by the organism In order to do this they need a supply of amino acids Plants and animals differ in their ability to manufacture manufacture their necessary amino acids Higher plants are capable of producing all of their life-essential amino acids Human adult cells however can produce only 11 of their 20 necessary amino acids The remaining nine called essential amino acids are obtained by eating foods that already contain them Some proteins proteins called transport proteins carry substances from one place in the body to another Other transport transport proteins are located in cell membranes These proteins shuttle nutrients and waste products from one side of the membrane to the other Many proteins proteins make up the supportive elements that provide biological structures with strength and protection Regulatory proteins help to prevent the depletion of nutrients in tissues or the harmful accumulation of the products of respiration In contrast to proteins carbohydrates do not contain nitrogens Rather they are formed from various arrangements of carbon hydrogen and oxygen Carbohydrates can be divided into three major groups monosaccharides disaccharides and polysaccharides Molecules of monosaccharides monosaccharides or simple sugars contain from three to nine carbon atoms most commonly five or six Two of the most important simple sugars are glucose also 12 EXAMINING BASIC CHEMICAL MOLECULES
INTRODUCTION known as dextrose and fructose or fruit sugar Two simple sugar molecules are linked to each other in a disaccharide or double sugar Many carbohydrates are isomers that is they have the same numbers of particular atoms but different molecular structures Glucose fructose and galactose a monosaccharide monosaccharide part of lactose for example are all isomers with the identical formula of C6H12O6 While carbohydrates provide important structural structural functions in cells they are better known as the primary sources of energy utilized by most life-forms Glucose which circulates in the blood of higher animals animals is absorbed by the cells where it participates in biochemical reactions that energize the metabolic processes Glycogen which consists of branching chains of glucose molecules is stored in the liver and muscles of higher animals to be broken down into glucose during times of muscular activity In addition some carbohydrates in the form of polysaccharides function as structural components in certain animals animals For example chitin which is similar to cellulose cellulose makes up the exoskeleton or hard covering of insects and other animals classified as arthropods These include crustaceans and arachnids Fatty acids or lipids form a secondary energy source for many organisms These molecules although composed of the same basic elements as carbohydrates carbon hydrogen and oxygen oxygen are distinguished by the linkages or bonds 13
connecting the elements The unique bonding and chemical arrangement of fatty acids determines the molecules function and metabolism Nucleic acids the amino acids of proteins carbohydrates carbohydrates and fatty acids all are naturally occurring chemical compounds Each is also capable of being broken down to yield discrete components These four basic chemical molecules are critical to life and understanding and researching their structure and function has led to many important insights in biology biology chemistry medicine and other fields 14 EXAMINING BASIC CHEMICAL MOLECULES
CHAPTER 1 Nucleic Acids A nucleic acid is a naturally occurring chemical compound that is capable of being broken down to yield phosphoric acid sugars and a mixture of organic bases purines and pyrimidines Nucleic acids are the main information-carrying molecules of the cell and by directing the process of protein synthesis they determine the inherited characteristics of every living thing The two main classes of nucleic acids are deoxyribonucleic acid DNA and ribonucleic acid RNA DNA is the master blueprint for life and constitutes the genetic material in all free-living organisms and most viruses RNA is the genetic material of certain viruses but it is also found in all living cells where it plays an important role in certain processes such as the making of proteins 15
