ECE 593-728 Chapter Two CHEMICAL COMPOSITION OF THE BODY • What is an atom? An atom is the smallest indivisible units of matter; each type of atom is also called a chemical element. An atom is made up of protons, electrons and neutrons. These three subatomic particles characterize the chemical properties of an atom. Protons, Neutrons and Electrons • The protons are positively charged, while the neutrons are negatively charged. Both the protons and neutrons are confined to a very small volume at the center of an atom called the atomic nucleus. On the other hand, electrons are negatively charged and they can be found revolving around the nucleus. Atomic number • This is one characteristic that distinguish one chemical element from another. An atomic number is the specific number of protons found in that chemical element. For example hydrogen has one proton, thus its atomic number is one. Looking at the periodic table, one can also be able to deduct the atomic number; elements in the periodic table are usually numbered according to their atomic numbers. Cont.. • Hydrogen (H) has an atomic number of one; lithium (Li) has an atomic number of three and so on. What is a molecule? A molecule is made up of two or more atoms. A good example is water, a molecule of water contains two hydrogen atoms and one oxygen atom, thus water can be represented as H2O. What is an Ion? • An atom is characterized as an ion when it loses or gains one or more electrons. For example, when a sodium atom (Na), which has 11 electrons, loses one electron, it becomes a sodium ion with a net positive charge; it still has 11 protons, but the loss of one electron leaves it without only 10 electrons remaining. Cont… • On the other hand a chlorine atom which has 17 electrons can gain an electron and become a chloride ion with a net negative charge. This chloride ion now has 18 electrons and 17 protons. Ions that have a net positive charge are called cations, while those that have a net negative charge are called anions. CLASSES OF ORGANIC MOLECULES • What are organic molecules? These are molecules that have their basic skeleton made of carbons atoms, hydrogen, oxygen and sometimes nitrogen atoms. Generally organic molecules in the body can be classified into one of four groups: carbohydrates, lipids, proteins and nucleic acid. Carbohydrates • Carbohydrates are the abundant of the four main organic molecules. They fill numerous roles in living things, such as the storage and transport of energy (starch, glycogen) and structural components (cellulose in plants, chitin in animals). Most carbohydrates taste sweet, and the carbohydrates include the substances known as sugars. Cont.. • The simplest sugars are known as monosaccharides, a good example of a monosaccharide is glucose. Glucose is the major monosaccharide found in the blood, when two monosaccharide are linked together they form a disaccharides. An example of a disaccharide is table sugar also known as sucrose. Cont… • When many monosaccharide are linked together they form a molecule known as a polysaccharide. An example of a polysaccharide is glycogen. Glycogen is found in animal cells and it serves as primary short term energy storage in animal cells. It is made primarily by the liver and the muscles. Lipids • Lipids are fat-soluble, naturally occurring molecules; unlike carbohydrates lipids are insoluble in water. The main biological functions of lipids include energy storage, acting as structural components of cell membranes, and participating as important signaling molecules. Lipids can be divided into four subclasses namely: fatty acids, triglycerides, phospholipids, and steroids. Proteins • Proteins are large organic compounds made up of amino acids (amino acids are organic molecules that are made of carbon, nitrogen and hydrogen atoms). These amino acids are arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. Example illustrating the formation of a peptide bond Cont… • Peptide bonds are formed between the amino and carboxyl group. These bonds can be broken by hydrolysis to yield individual amino acids. The figure on the previous slide illustrates the hydrolysis of a protein. PROTEIN STRUCTURE • Proteins are characterized of three types of structures namely: primary, secondary, tertiary and quaternary structure. Primary Protein Structure The primary structure of a protein refers to the number and sequence of amino acids in the protein. The primary structure of a protein is very important in the identification of a protein. Diagram showing the primary structure of a protein Cont.. • Secondary Protein Structure The secondary protein structure is the specific geometric shape caused by intramolecular and intermolecular hydrogen bonding of amide groups. The most common secondary structures of proteins are the alpha helices and beta sheet. Diagram showing the secondary structure of a protein Cont… • Tertiary Protein Structure The third type of structure found in proteins is called tertiary protein structure. The tertiary structure is the final specific geometric shape that a protein assumes. This final shape is determined by a variety of bonding interactions between the "side chains" on the amino acids. These bonding interactions may be stronger than the hydrogen bonds between amide groups holding the helical structure. As a result, bonding interactions between "side chains" may cause a number of folds, bends, and loops in the protein chain. Different fragments of the same chain may become bonded together. • The figure on the next slide, shows the difference between primary, secondary and tertiary protein structures: Different protein structures Quaternary Protein Structure • The quaternary protein structure involves the clustering of several individual peptide or protein chains into a final specific shape. A variety of bonding interactions including hydrogen bonding, salt bridges, and disulfide bonds hold the various chains into a particular geometry. Figure showing quaternary protein structure Nucleic Acids • These organic molecules are responsible for the storage, expression, and transmission of genetic information. It is the expression of genetic information that determines whether a cell is a muscle cell or a nerve cell. There are basically two classes of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).