I. Oxidation-Reduction Reactions (redox reactions) Are Common in Biological SystemsBIOL 1020 - CHAPTER 2 LECTURE NOTESChapter 2: The chemical context of lifeYou must understand chemistry to understand life (and to pass this course)!Overview: In many ways, life can be viewed as a complicated chemical reaction. Modern models of how life works at all levels typically have at least some aspect of chemistry as a major component or underpinning.I. Elements and AtomsA. elements – substances that cannot be further broken down into other substances (at least by ordinary chemical reactions)1. every element has a chemical symbol (H for hydrogen, O for oxygen, etc.); this is most familiar from the periodic table2. there are 92 naturally occurring elements, from hydrogen up to uranium-4 elements (oxygen, carbon, hydrogen, and nitrogen = O, C, H, N) make about 96% of the mass of most living things-8 others are consistently present in small amounts in living things (Ca, P, K, S, Na, Mg, Cl, Fe)-several others are typically found only in trace amounts (trace elements); these tend to vary considerably in amount and even presence depending on the type of organismB. an atom is the smallest unit of an element that still retains the properties of that elementC. atoms consist of subatomic particles1. electron - contributes no significant mass to the atom, but carries a (-1) electrical charge2. proton - contributes a mass of approximately 1 mass unit, and carries a (+1) electrical charge3. neutron - contributes a mass of approximately 1 mass unit, and carries no net electrical charge4. protons and neutrons are found in the nucleus (center) of an atom5. elements differ from each other because they contain different numbers of protons (all hydrogen atoms contain 1 proton, all carbon atoms contain 6 protons, all oxygen atoms contain 8 protons, etc.)-atomic number = number of protons in the nucleus-the periodic table has elements arranged largely according to atomic number1 of 6BIOL 1020 - CHAPTER 2 LECTURE NOTES6. protons + neutrons determine atomic mass-each contribute ~1 atomic mass unit (amu, or Dalton)-atoms that have the same number of protons but have different numbers of neutrons (therefore different masses) arereferred to as isotopesD. atomic nuclei can undergo changes (decay)1. some elements are more stable than others2. some isotopes are more stable than others (most unstable = radioisotopes)3. decay rates are statistical averages, and are used for measuring time passage in many areas of science (carbon dating, etc.)4. the radiation emitted upon decay (alpha, beta, and/or gamma) can be used as a tool for experiments; can also be used medically; has other uses and dangers (nuclear power, nuclear bombs, radiation poisoning, etc.)5. radiation can cause mutations in DNA, can interfere with cell divisionE. electrons occupy orbitals surrounding the nucleus and move at the speed of light1. because ATOMS are electrically neutral the number of electrons an atom has always equals the number of protons2. electrons can exist at different energy levels, which correspond to orbitals-the further away an orbital carries an electron from the nucleus, the higher the energy level of the electron-electrons with similar energies make up an electron shell3. the outer electron(s) are known as the valence electron(s); collectively, they occupy the valence shell4. the chemical properties of an atom are largely determined by the valence electronsF. the science of chemistry mostly involves study of how electrons move about the nucleus, store energy, and determine chemical properties of substances as a resultII. Describing Atomic CombinationsA. atoms combine to form molecules and compounds1. molecule – two or more atoms held together by covalent bonds (defined later)2 of 6BIOL 1020 - CHAPTER 2 LECTURE NOTES-may be composed of one or more elements (examples: O2, H2O)-not all substances are molecular (NaCl, table salt, isn’t)-if a substance is molecular, then an individual molecule is the smallest unit of the substance that exhibits the properties of the substance-thus, a molecule differs in its physical and chemical properties from the elements that make it up2. compound - a specific combination of two or more different elements chemically combined in a fixed ratio-compounds have unique physical and chemical properties that differ from those of the elements used to make it-some compounds are held together by covalent bonds and are therefore molecular; some are held together by ionic bonds (defined later)B. chemists use two types of formulas to describe substances1. chemical formula - a shorthand formula showing the number of atoms of each element present in a molecule-often called molecular formula if a molecule is involved; examples: H2O, CO2, O2, C6H12O6-follows simplest ratio for ionic substances (NaCl, etc.)2. structural formula - shows the arrangement of atoms in a molecule-examples:water H─O─Hcarbon dioxide O═C═Omolecular oxygen O═OC. the number of units of a substance are described using the mole1. molecular mass is the sum of the atomic masses of the atoms in the molecule2. since the actual mass of an atom is extremely small, it is convenient in the real world to work with a large number of atoms at the same time3. The amount of a substance that in grams has the same number as the atomic mass is a mole4. Thus, water has molecular mass 1+1+16 = 18; a mole of water has a mass of 18 g3 of 6BIOL 1020 - CHAPTER 2 LECTURE NOTES5. The mole is simply a conversion factor from the small scale of atomic mass units to the more familiar gram scale-the factor represents the number of units (molecules or atoms) in a mole-this factor, called Avogadro’s number, is 6.02 x 1023 atoms or moleculesIII. Chemical Bonds Hold Molecules Together and Store EnergyA. recall that electrons in the outermost shell of an atom (valence electrons) determine the chemical behavior of the atom, i.e. what type and how many chemical bonds it can readily formB. most atoms in biological systems seek to have 8 electrons in their outermost shell (hydrogen seeks to have 0 or 2 electrons in its outermost shell)C. since atoms have the same number of electrons as protons, they meet this need to have a full valence shell by sharing, giving up, or acquiring electrons from other atoms; this forms chemical bonds1. a chemical bond is a reduced energy state2. bond energy is the amount of energy required to break a particular chemical