PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 9/e by Shier, Butler, and Lewis

Chapter Two Chemical Basis of Life

Chemistry and Biochemistry Chemistry considers the composition of substances and how they change. The chemistry of living organisms is biological chemistry or biochemistry. Biochemistry has been important in explaining physiological processes and in improving medicine.

Matter and Elements Matter is anything that has weight and takes up space. All matter is composed of elements. Elements exist is their pure form or in chemical combinations called compounds. Elements are composed of atoms.

Atomic Structure Nucleus: center of the atom, containing protons and neutrons Protons: positively charged particles Neutrons: particles which lack charge Electrons: very small, negatively charged particles which encircle the nucleus

Figure 2.1

Isotopes Atomic number is the number of protons. It is the same for all atoms of an element. Atomic weight is the number of protons and neutrons. Atoms that have the same atomic number, but different atomic weights are isotopes.

Stable and Radioactive Isotopes Isotopes that do not decompose are called stable isotopes. Isotopes that have unstable nuclei that decompose are called radioactive isotopes. Radioactive isotopes release energy or particles until they reach a stable form.

Atomic Radiation Alpha radiation consists of particles from atomic nuclei, two protons and two neutrons. These particles are heavy, move slowly, and do not penetrate matter.

Atomic Radiation Beta radiation consists of smaller electrons that travel fast and penetrate matter. Gamma radiation is similar to X-radiation and is the most penetrating of these forms.

Molecules Two or more atoms combine to form a molecule. Molecules are distinctive from the elements of which they are composed. A molecular formula illustrates the number and type of atoms found in a molecule.

Atomic Structure Atoms, such as Helium, whose outermost electron shells are filled, have stable structures and are chemically inactive or inert. Atoms with incompletely filled outer shells tend to gain or lose electrons in ways that empty or fill their outer shells and create a stable structure.

Molecular Bonding Ions are formed when atoms gain or lose electrons.

Molecular Bonding Ionic or electrovalent bonds are formed by the attraction of oppositely charged ions.

Molecular Bonding Covalent bonds are formed by the sharing of electrons between atoms.

Molecular Bonding Hydrogen bonds are weak bonds between polar molecules.

Polar Molecules Covalent bonds can be formed where the electrons are not shared equally. This results in a polar molecule that has equal numbers of protons and electrons, but one atom has more that its share of electrons, becoming negative, and one atom has less, becoming positive.

These polar bonds occur where hydrogen bonds to oxygen or nitrogen. Polar Molecules These polar bonds occur where hydrogen bonds to oxygen or nitrogen.

Chemical Reactions Synthesis Reaction: A + B = AB Decomposition Reaction: AB = A + B Exchange Reaction: AB + CD = AD + CB Reversible Reactions can proceed in either direction

Reversible Reactions Many chemical reactions are reversible. The direction in which the reaction proceeds depends on many factors such as: - the proportions of products - reactants - amount of energy - presence of catalysts - molecules that influence the rate of reaction, but are not consumed in the reaction.

Acids, Bases, Salts Polarity of water causes dissociation of salts, releasing ions.

Acids, Bases, Salts Electrolytes release ions in water. Acids release hydrogen ions (H+). Bases release ions that combine with H+. Salts are formed by the reaction between an acid and a base.

Acid and Base Concentrations Hydrogen ions concentrations are measured in grams of ions per liter of solutions. The pH scale illustrates the hydrogen ions concentration in a convenient form. Pure water ionizes only slightly and results in equal numbers of hydrogen and hydroxyl ions, pH 7, chemically neutral.

Hydrogen Ion Concentration Solutions with more hydrogen ions than hydroxyl ions are acidic with ph values of less than 7. Solutions with more hydroxyl ions than hydrogen ions are basic with ph values of greater than 7.

Body Fluid pH Changes Fluids in the human body function in a narrow ph range. Blood ph of 7.5 to 7.8 is alkalosis, resulting in agitation and dizziness. Blood ph of 7.0 to 7.3 is acidosis, resulting in disorientation and fatigue.

Figure 2.9

Water Oxygen Carbon Dioxide Inorganic Salts Inorganic Substances Water Oxygen Carbon Dioxide Inorganic Salts

Water Water is the most abundant compound in living material. It makes of 2/3 of the weight of an adult human.

Water Substances dissolve in water, making it possible for metabolic reactions to occur. Water aids in transport of substances. Water absorbs and transports heat.

Oxygen and Carbon Dioxide Oxygen is used to release energy from nutrient molecules. Carbon dioxide is produced as a waste product when energy is released during certain metabolic reactions.

Inorganic Salts Inorganic salts are the source of many important ions, including Na+, Cl-, K+, Ca++, and many others. These play a role in metabolic reactions and must be maintained in appropriate concentrations. This is called electrolyte balance.

Organic Substances Organic molecules are carbon based molecules containing hydrogen and often oxygen. Important groups of organic substances in cells include carbohydrates, lipids, proteins, nucleic acids.

Carbohydrates Carbohydrates: water-soluble molecules containing carbon, hydrogen, oxygen Sugars: monosaccharides, disaccharides

Carbohydrates Polysaccharides: built of simple sugars: starch, fiber, glycogen

Lipids Three fatty acids combine with glycerol to form a triglyceride.

Lipids Fatty acids can be saturated or unsaturated. Phospholipids contain two fatty acids and a phosphate group.

Lipids Steroids are lipids composed of connected carbon rings, ex: cholesterol.

Saturated vs. Unsaturated Fats A diet rich in saturated fat increases a person’s risk of atherosclerosis. It is healthful to substitute unsaturated fats. Saturated fats are found in fatty foods that are solid at room temperature. Unsaturated fats are found in foods that are liquid at room temperature.

Proteins Wide range of functions Chain of amino acids of varying lengths Amino acids contain a central carbon, an amino group, a carboxyl group, and a side chain (R group) Amino acids are linked in a peptide bond joining the amino of one and carboxyl group of another amino acid

Levels of Protein Structure Primary: amino acid sequence Secondary: coil or sheet formed by hydrogen bonds between the amino acids Tertiary: three dimensional shape created by hydrogen and covalent bonds Quarternary: association of several separate protein chains

Figure 2.18

Nucleic Acids RNA ribose single strand aid in protein synthesis DNA deoxyribose double stranded store genetic information

Nucleic Acids Large, complex molecules Chains of nucleotides Nucleotides are composed of a sugar, a phosphate group, and one of five nitrogen bases

Figure 2.20a

Figure 2.20b