8 20 2013 The chemical basis of life Part I Chapter 2 Early thoughts on the nature of living things Vitalism proposes that functions of a living organism are due to a vital force and that life cannot be explained by the laws of physics and chemistry Organic molecules were thought to be fundamentally distinct from inorganic molecules http en wikipedia org wiki File Sanzio 01 Plato Aristotle jpg Evidence against vitalism Friedrich W hler synthesizes urea an organic molecule from inorganic components 1828 and led to the great tragedy of science the slaying of a beautiful hypothesis by an ugly fact Louis Pasteur refutes spontaneous generation ti 1859 and d never will ill th the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment Stanley Miller shows that conditions on early Earth favored the synthesis of organic compounds from inorganic precursors 1952 http en wikipedia org wiki File Friedrich W C3 B6hler Stich jpg http bioweb wku edu courses Biol115 Wyatt Sci method Pasteur png http en wikipedia org wiki File Miller1999 jpg 1 8 20 2013 Living things are and subject to the laws of physics and chemistry All matter including living things is subject to the laws of physics and chemistry mechanism Matter is anything that takes up space and has mass Matter is made up of elements a pure chemical substance Elements consist off atoms t th the smallest unit of matter that retain the properties of that element Somewhere in the transition between atoms and cells life emerges Subatomic structure determines the chemical behavior of an element Proton number Neutron number Electron configuration Subatomic structure determines the chemical behavior of an element Atom 2 8 20 2013 Subatomic structure determines the chemical behavior of an element Atomic nucleus Subatomic particles Protons Electrons Neutrons Compare to Figure 2 2 The periodic table provides information about the subatomic structure chemistry of elements Figure 2 5 The periodic table provides information about the subatomic structure chemistry of elements Element name Atomic proton number Element symbol Atomic mass in Daltons Figure 2 5 3 8 20 2013 Some elements are essential for life Essential elements 25 are required for life O C H and N are the mostt abundant b d t elements l t in living things Trace elements are essential elements required by living organisms only in very small amounts Neutron number determines the isotope Isotopes are elements that differ in their numbers of neutrons and therefore their atomic masses Stable isotopes p do not lose subatomic particles Unstable or radioactive isotopes decay spontaneously emitting particles and energy Isotopes of hydrogen 1H Protium Common Isotope 2H 3H Deuterium Tritium Stable Isotope Radioactive Isotope 3He 4 8 20 2013 Electron configuration Electrons are arranged in shells that surround the atomic nucleus Electron shells have different energy levels with outer shells having greater potential energy Electron shells contains contain a fixed number of electrons housed in orbitals Figure 2 5 Atomic orbitals Orbitals are Each orbital holds Orbitals have Figure 2 3 Atomic orbitals Orbitals are Each orbital holds Orbitals have Figure 2 4 5 8 20 2013 Electron configuration The configuration of the valence electrons outermost electrons determines the chemical behavior of that element Atoms with complete valence shells are Atoms with incomplete valence shells are Some elements are essential for life Essential elements 25 are required for life O C H and N are the mostt abundant b d t elements l t in living things Trace elements are essential elements required by living organisms only in very small amounts The periodic table provides information about the subatomic structure chemistry of elements Figure 2 5 6 8 20 2013 Chemical bonds between atoms form molecules Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms to form molecules These interactions usually result in atoms staying close together held by attractions called chemical bonds Covalent bonds A strong chemical bond in which two atoms share one or more pairs of valence electrons Example H2O Name and Molecular Formula Lewis Dot El t Electron distribution Structure and Structural Diagram Formula SSpace filling Model Water H2O Compare to Figure 2 10 Covalent bonds A strong chemical bond in which two atoms share one or more pairs of valence electrons Example H2O Differences in electronegativity the attraction of an atom for electrons can create bonds in which electrons are shared unequally unequally In polar covalent bonds O H H H2O In nonpolar covalent bonds Compare to Figure 2 10 7 8 20 2013 Ionic bonds A chemical bond resulting from the attraction of oppositely charged ions Example salts like NaCl Na Na Sodium atom Cl Cl Chlorine atom Compare to Figure 2 12 Na Cl Na Sodium ion a cation Cl Chloride ion an anion Sodium chloride NaCl Hydrogen bonds Hydrogen bonds form when a hydrogen atom covalently bound to an electronegative atom is attracted to another electronegative atom Hydrogen bonds are very dynamic constantly being made broken and reformed Although individually weak the cumulative effect of hydrogen bonds can effect the chemistry and 3D shape Hydrogen bonds can of molecules be intramolecular or Figure 2 11 intermolecular Molecules have 3D shape Figure 2 13 8 8 20 2013 Chemical reactions make and break bonds 2 H2 O2 Reactants 2 H2O Reaction Products Hydrogen bonding of water provides it with unique chemical properties that support life Figure 2 11 Water moderates temperature The specific heat of water the amount of energy that needs to be absorbed lost by water to increase decrease its temperature moderates temperatures 9 8 20 2013 Water displays cohesion and adhesion Cohesion is the attraction of water molecules or any like molecules often by hydrogen bonding Adhesion Adh i is i attraction tt ti off different molecules often by hydrogen bonding Example Water transport in plants see Figure 2 20 http dining byu edu mix images coloredFlowers jpg Water expands when frozen so ice is less dense than water Figure 2 18 Water readily dissolves polar molecules A solution is a homogeneous mixture of two or more substances The h solvent l is the h dissolving agent The solute is the dissolved substance An aqueous solution is one in which the solvent is water Compare to Figure 2 16 10 8 20 2013 Substances can be categorized by their affinity for