CHAPTER 2 The Chemical Basis of Life

Thomas Eisner and the Chemical Language of Nature Thomas Eisner pioneered _______ __________ the study of the chemical language of nature He studies how insects communicate via chemical messages

Water in three different states: 5 States of matter

The emergence of biological function starts at the chemical level ATOMS AND MOLECULES The emergence of biological function starts at the chemical level Everything an organism is and does depends on chemistry Chemistry is in turn dependent on the arrangement of atoms in molecules In order to understand the whole, biologists study the parts (reductionism)

A ________ _________ D. Organ: Flight muscle of a moth Rattlebox moth C. Cell and tissue: Muscle cell within muscle tissue Myofibril (organelle) B. Organelle: Myofibril (found only in muscle cells) Actin Myosin Atom A. Molecule: Actin

About ____ different chemical elements are essential to _____ A chemical _____ is a substance that cannot be broken down to other substances by ordinary chemical means About ____ different chemical elements are essential to _____ lead

Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter, but there are other elements necessary for life _________ Table 2.2

Goiters are caused by iodine deficiency Figure 2.2

2.4 Atoms consist of protons, ________, and electrons The smallest particle of an element is an _____ Different ______ have different types of atoms

The nucleus is surrounded by electrons An atom is made up of protons and neutrons located in a central nucleus The nucleus is surrounded by electrons 2 Protons Nucleus 2 Neutrons 2 Electrons A. Helium atom

Neutrons are electrically _______ Each atom is held together by attractions between the positively charged protons and ________charged electrons Neutrons are electrically _______ 6 Protons Nucleus 6 Neutrons 6 Electrons B. Carbon atom

Atoms of each element are distinguished by a specific number of protons The number of neutrons may vary Variant forms of an element are called ________ Some isotopes are ________

2.5 Connection: Radioactive isotopes can help or harm us Radioactive isotopes can be useful tracers for studying biological processes PET scanners use radioactive isotopes to create anatomical images Figure 2.5A Figure 2.5B

2.3 Elements can combine to form compounds Chemical elements combine in fixed ratios to form _________ Example: sodium + chlorine  sodium chloride Reactants Products

2.6 Electron arrangement determines the chemical properties of an atom Electrons are arranged in _______ The outermost shell determines the chemical properties of an atom In most atoms, a full outer shell holds _____ electrons

Atoms whose shells are not full tend to interact with other atoms and ___, ____, or ______ electrons Outermost electron shell (can hold 8 electrons) Electron First electron shell (can hold 2 electrons) HYDROGEN (H) Atomic number = 1 CARBON (C) Atomic number = 6 NITROGEN (N) Atomic number = 7 OXYGEN (O) Atomic number = 8 Figure 2.6

2.7 Ionic bonds are attractions between ions of opposite charge When atoms gain or lose electrons, charged atoms called ions are created An electrical attraction between ions with opposite charges results in an ionic bond – + Na Cl Na Cl Na Sodium atom Cl Chlorine atom Na+ Sodium ion Cl– Chloride ion Figure 2.7A Sodium chloride (NaCl)

2.8 Covalent bonds, the _____ of electrons, join atoms into molecules Some atoms share outer shell electrons with other atoms, forming covalent bonds Atoms joined together by covalent bonds form molecules

Chemical reactions rearrange matter REARRANGEMENTS OF ATOMS Chemical reactions rearrange matter In a chemical reaction: reactants interact atoms rearrange products result 2 H2 + O2  2 H2O

2.15 The chemistry of life is sensitive to acidic and basic conditions A compound that releases H+ ions in solution is an acid, and one that accepts H+ ions in solution is a base Acidity is measured on the pH scale: 0-6 is acidic 8-13 is basic OH- Hydroxide Ion Alkaline Pure water and solutions that are neither basic nor acidic are neutral, with a pH of 7

(Higher concentration of H+) (Lower concentration of H+) pH scale The pH scale H+ OH– Lemon juice; gastric juice (Higher concentration of H+) Increasingly ACIDIC Grapefruit juice Acidic solution Tomato juice Urine NEUTRAL [H+] = [OH–] PURE WATER Human blood Seawater Neutral solution (Lower concentration of H+) Increasingly BASIC Milk of magnesia Household ammonia Household bleach Oven cleaner Basic solution

Cells are kept close to pH 7 by buffers Buffers are substances that resist pH change They accept H+ ions when they are in excess and donate H+ ions when they are depleted Buffers are not foolproof