CHAPTER 2 The Chemical Basis of Life Modules 2.1 – 2.8

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

Rattlebox moths release a chemical that spiders don’t like This spider caught a rattlebox moth and then let it go

2.1 The emergence of biological function starts at the chemical level ATOMS AND MOLECULES 2.1 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)

Molecules and ecosystems are at opposite ends of the biological hierarchy Each level of organization in the biological hierarchy builds on the one below it At each level, new properties emerge

A biological hierarchy D. Organ: Flight muscle of a moth A biological hierarchy Rattlebox moth C. Cell and tissue: Muscle cell within muscle tissue Myofibril (organelle) B. Organelle: Myofibril (found only in muscle cells) Actin Myosin Figure 2.1 Atom A. Molecule: Actin

2.2 Life requires about 25 chemical elements A chemical element is a substance that cannot be broken down to other substances by ordinary chemical means About 25 different chemical elements are essential to life

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

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

2.4 Atoms consist of protons, neutrons, and electrons The smallest particle of an element is an atom Different elements 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 Figure 2.4A A. Helium atom

Neutrons are electrically neutral Each atom is held together by attractions between the positively charged protons and negatively charged electrons Neutrons are electrically neutral 6 Protons Nucleus 6 Neutrons 6 Electrons Figure 2.4B 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 isotopes Some isotopes are radioactive Table 2.4

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

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

Atoms whose shells are not full tend to interact with other atoms and gain, lose, or share 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)

Sodium and chloride ions bond to form sodium chloride, common table salt Na+ Cl– Figure 2.7B

2.8 Covalent bonds, the sharing 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

Molecules can be represented in many ways Table 2.8