Chapter 02 Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

Chapter 2 Chemical Basis of Life 2

2.1 Introduction 3

Chemistry deals with the composition of matter and how it changes. A knowledge of chemistry is necessary for the understanding of physiology because of the importance of chemicals in body processes.

2.2 Structure of Matter 5

Matter is anything that has weight (mass) and takes up space. Elements and Atoms Matter is anything that has weight (mass) and takes up space. All matter is composed of elements. Living organisms require about 20 elements, of which oxygen, carbon, hydrogen, and nitrogen are most abundant. Elements are composed of atoms; atoms of different elements vary in size, weight, and interaction with other atoms. Attractions between two or more atoms are called chemical bonds. 6

Table 2.1

Electrons are much smaller and bear a negative charge. Atomic Structure An atom consists of a nucleus containing protons and neutrons, with electrons in orbit around the nucleus in shells. Protons, with a positive charge, are about equal in size to neutrons, which have no charge. Electrons are much smaller and bear a negative charge. An electrically neutral atom has equal numbers of protons and electrons. 8

The number of protons denotes the atomic number of an element; the number of protons plus the number of neutrons approximates the atomic weight. Atoms with the same atomic number, but different weights are isotopes of an element. Unstable isotopes are radioactive Common forms of radiation given off Alpha particles Beta particles Gamma radiation Half-life –the time required for an isotope to lose half of its radioactivity.

Fig 2.1 10

Electrons are found in shells around the nucleus. Bonding of Atoms Atoms form bonds by gaining, losing, or sharing electrons; determines the chemical activity Electrons are found in shells around the nucleus. The first energy shell holds a maximum of two electrons. The other energy shells each hold a maximum of eight electrons when on the outside. Elements that have their outermost shells filled, are stable structures that are chemically inert. 11

Fig 2.2 12

Oppositely-charged ions attract each other and form an ionic bond. Bonding of atoms, cont Atoms with incompletely filled outer shells tend to be reactive in order to form stable outer shells of 8 electrons. When atoms gain or lose electrons, they become ions with a charge. Whether they gain or lose will depend on how many electrons they have in the outer shell to start with. Oppositely-charged ions attract each other and form an ionic bond. Form crystal arrays not molecules Formula gives the ratio of ions, not the actual numbers 13

Fig 2.4 14

Bonding, cont. Covalent bonds are formed when atoms share electrons to become stable with filled outer shells. One pair of electrons shared between two atoms forms a single covalent bond. Two pairs of electrons shared between atoms form a double covalent bond. Three pairs of electrons shared between two atoms forms a triple covalent bond. 15

Fig 2.5 16

Bonding, cont. A polar molecule has a covalent bond in which the electrons are not shared equally. A hydrogen bond forms from a slightly positive H end of a polar molecule being attracted to the negative N or O end of another polar molecule. 17

Fig 2.6 18

Molecules and Compounds A molecule is formed when two or more atoms combine. If atoms of the same element combine, a molecule of that element is formed (O2 is the oxygen molecule) If atoms of different elements combine, the molecule can also be called a compound. Compounds always have a definite kind and number of atoms. 19

Fig 2.7 20

Table 2.3 21

Ex: Glucose = C6H12O6 , water = H2O Formulas A molecular formula represents the numbers and types of atoms in a molecule. Ex: Glucose = C6H12O6 , water = H2O Various representations, called structural formulas, can be used to illustrate how atoms are joined and arranged in molecules. 22

Fig 2.8 23

Fig 2.9 24

Chemical Reactions A chemical reaction occurs as bonds are formed or broken between atoms, ions, or molecules. Those changed by the reaction are the reactants; those formed are the products. Two or more atoms or molecules can be joined during synthesis reactions. A + B  AB Larger molecules can be broken into smaller ones during decomposition reactions. AB  A + B 25

Chemical reactions, cont. Exchange reactions occur as parts of molecules trade places. AB + CD  AD + CB Reversible reactions are symbolized by using two arrows. AB + CD  AD + CB Catalysts influence the speed of chemical reactions without being used up in the process. 26

Substances that release ions in water are called electrolytes. Acids and Bases Substances that release ions in water are called electrolytes. Electrolytes that release hydrogen ions in water are called acids. Electrolytes that release ions that combine with hydrogen ions in water are called bases. The concentrations of H+ and OH- in the body are very important to physiology. pH represents the concentration of hydrogen ions [H+] in solution. 27

pH scale ranges from 0 to 14 A pH of 0 to less than 7 indicates the presence of more hydrogen ions and is considered acidic. The lower the pH, the more acidic. A pH of 7 indicates a neutral solution with equal numbers of hydrogen ions and hydroxide (OH-) ions. A pH of greater than 7 to 14 indicates the presence of more hydroxide ions and is considered basic or alkaline. The higher the pH, the more basic. Between each whole number of the pH scale there is a tenfold difference in hydrogen ion concentration. A pH of 3 is ten times more acidic than a pH of 4. Buffers are chemicals that combine with excess acids or bases to help minimize pH changes in body fluids. 28

Fig 2.11 29

2.3 Chemical constituents of cells 30

Organic compounds contain both hydrogen and carbon. All other compounds are considered inorganic and they usually dissolve in water and release ions, making them electrolytes. 31

Water can absorb and transport heat. Water is the most abundant compound in living things and makes up two-thirds of the weight of adults. Water is an important solvent so most metabolic reactions occur in water. Water is important in transporting materials in the body since it is a major component of blood. Water can absorb and transport heat. Water acts as a reactant in many metabolic reactions in the body 32

Inorganic compounds, cont Oxygen - needed to release energy from nutrients and is used to drive the cell's metabolism. Carbon Dioxide - released as a waste product during energy-releasing metabolic reactions. Salts Salts provide necessary ions including sodium, chloride, potassium, calcium, magnesium, phosphate, carbonate, bicarbonate, and sulfate. These electrolytes play important roles in many of the body's metabolic processes. 33

Table 2.4 34

Disaccharides (double sugars) – lactose, sucrose, maltose Organic Substances Carbohydrates Carbohydrates provide energy for cellular activities and are composed of carbon, hydrogen, and oxygen. The smallest carbohydrates are monosaccharides (simple sugars) – glucose, fructose, galactose, ribose, deoxyribose Disaccharides (double sugars) – lactose, sucrose, maltose Polysaccharides – many glucose molecules joined together; glycogen, starch 35

Fig 2.12 36

Fig 2.13 37

Those with one or more double bonds are called unsaturated fats. Lipids Lipids are organic substances that are insoluble in water and include fats, phospholipids, and steroids. Fats supply energy for cellular function, and are built from glycerol and three fatty acids. Fats have a smaller proportion of oxygen atoms than carbohydrates. Fatty acids with hydrogen at every position along the carbon chain are saturated fats Those with one or more double bonds are called unsaturated fats. 38

Fig 2.14 39

Lipids, cont Phospholipids contain glycerol, two fatty acids, and a phosphate group, and are important in cell structures. Steroids are complex ring structures, and include cholesterol, which is used to synthesize the sex hormones and several hormones from the adrenal glands. 40

Fig 2.15 41

Fig 2.16 42

Proteins Proteins have a great variety of functions in the body – as structural materials, energy sources, certain hormones, receptors on cell membranes, antibodies, and enzymes to catalyze metabolic reactions. Proteins contain C, O, H, and N (nitrogen) atoms; some also contain S (sulfur). 43

Proteins, cont Building blocks of proteins are the amino acids, each of which has a carboxyl group, an amino group and a side chain called the R group. Fig 2.17 44

Proteins have complex shapes held together by hydrogen bonds. Proteins, cont. Proteins have complex shapes held together by hydrogen bonds. Primary structure – sequence of amino acids Secondary structure – pleated or twisted into a coil Tertiary – more pleats and twists into a globular form Quaternary structure – two or more strands join into a larger molecule 45

Fig 2.18 46

Protein shapes (conformations) determine how proteins function Proteins, cont. Protein shapes (conformations) determine how proteins function Denaturation – disruption of a protein’s shape by pH, temperature, radiation, or chemicals. Makes the protein nonfunctional. 47

Nucleic acids form genes and take part in protein synthesis. They contain carbon, hydrogen, oxygen, nitrogen, and phosphorus, which are bound into building blocks called nucleotides. Each nucleotide consists of a 5-carbon sugar, a phosphate group, and one of five nitrogenous bases. 48

Fig 2.20 49

Nucleic acids, cont. Nucleic acids are of two major types: DNA (with deoxyribose) and RNA (with ribose). RNA (ribonucleic acid) functions in protein synthesis and is single-stranded DNA (deoxyribonucleic acid) stores the molecular code in genes and is a twisted double strand. Adenosine triphosphate (ATP) is a modification of RNA that contains three phosphate groups that provides energy for chemical reactions in the body.   50

Fig 2.21 51

Fig 2.22 52