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Unformatted text preview: Chapter 2: The Chemical Basis of Life Biology is:
Based on the principles of chemistry and physics The study of living organisms, which are a collection of atoms and molecules An atom is the smallest functional unit that can not be broken down by chemical or physical means Each specific type of atom is a chemical element A Cell is the smallest living functional unit, all living Cell living organisms are composed of cells
1 An atom is composed of:
Three subatomic particles Three Protons- positive, found in nucleus, same Protons positive, number as electrons number Neutrons- neutral, found in nucleus, number Neutrons neutral, can vary can Electrons- negative, found in orbitals, same Electrons negative, orbitals same number as protons number Entire atom has no net electric charge Entire 2 1 3 4 2 Electrons occupy orbitals Electrons orbitals
S orbitals are spherical orbitals P orbitals are propeller or dumbbell orbitals are shaped shaped Each orbital can hold only 2 electrons Each An atom with more than 2 electrons has more than 1 orbital more 5 6 3 Nitrogen 7 Number of protons in an atom is its atomic number atomic Mass = # protons + # neutrons Mass Weight = average mass of all isotopes of the element average 8 4 Isotopes
Multiple forms of an element that differ in the number of neutrons neutrons 12C contains 6 protons and 6 neutrons 12 14C contains 6 protons and 8 neutrons 14 Atomic masses are averages of the weights of averages of different isotopes of an element different 9 Hydrogen(H), oxygen(O), carbon (C) and nitrogen (N) = 95% of the atoms in living organisms organisms Hydrogen and oxygen occur primarily in water water Nitrogen is found in proteins proteins Carbon iis the building block of all living Carbon s matter matter 10 5 11 Chemical bonds and molecules
Molecule Molecule 2 or more atoms bonded together bonded Molecular formula Molecular C6H12O6 Compound Compound Molecule composed of 2 or more elements elements
12 6 3 types of bonds
1. 2. 3. Covalent: share electrons Covalent: share Polar covalent: slight positive and negative charges negative Hydrogen: between molecules Ionic: positive and negative charges 13 Covalent bonds
Atoms share a pair of electrons pair Occurs between atoms whose outer electron shells are not full not Octet rule: atoms are stable when their outer Octet atoms electron shell is full (8 electrons) electron One exception is hydrogen, which fills its outer shell with 2 electrons outer 14 7 15 16 8 Polar covalent bonds
When two atoms with different electronegativities form a covalent bond, the electronegativities form shared electrons are more likely to be in the outer shell of the atom of higher electronegativity rather than the atom of electronegativity rather lower electronegativity electronegativity Polar covalent bonds occur because the distribution of electrons around the atoms creates a polarity, or difference in electric charge, across the molecule charge,
17 18 9 Hydrogen bonds
Weak polar covalent bonds Weak Represented as dashed or dotted lines Represented Collectively, can form strong bond overall Collectively Holds DNA strands together Holds Individually, weak bonds can form and Individually weak break easily break Substrate and enzyme bonding Substrate 19 20 10 Ionic bonds
An ion iis an atom or molecule that has ion s gained or lost one or more electrons gained one electrons It now has a net electric charge It Cations- net positive charge Cations Anions- net negative charge Anions Ionic bond occurs when a cation binds to cation binds an anion an 21 22 11 Properties of water
A solution is made up of the solution Solvent- liquid Solvent Solutes- substances dissolved in solvent Solutes Aqueous solution- water is the solvent Aqueous Ions and molecules that contain polar covalent bonds will dissolve in water covalent 23 Hydrophillic- “water-loving” Hydrophillic Readily dissolve in water Readily Ions and molecules that contain polar covalent bonds covalent Hydrophobic- “water-fearing” Hydrophobic Do not readily dissolve in water Do Nonpolar molecules like hydrocarbon Nonpolar Amphipathic molecule Amphipathic 24 12 H2O in 3 states of matter
Solid (ice), liquid (water), and gas (water Solid (ice), liquid (water), gas (water vapor) vapor) Changes in state, such as changes between the solid, liquid, and gas states of H2O, involve an input or release of energy O, energy Water is extremely stable as a liquid extremely 25 Water has many important functions in living organisms functions Participates in chemical reactions Participates Hydrolysis or dehydration Hydrolysis Provides force or support Provides Remove toxic waste components Remove Evaporative cooling Evaporative Cohesion and adhesion Cohesion 26 13 27 Acids and Bases
Pure water has the ability to ionize to a ionize to very small extent into hydrogen ions (H+) very and hydroxide ions (OH-) and In pure water In [H+][OH-] = [10-7 M][10-7 M] 10-14 M 28 14 Acids are molecules that release hydrogen release hydrogen ions in solution ions A strong acid releases more H+ than a strong than weak acid weak Bases lower the H+ concentration lower Some release OHSome Others bind H+ Others 29 pH
pH = log10 [H+] pH Acidic solutions are pH 6 or below pH pH 7 is neutral pH Alkaline solutions are pH 8 or above are 30 15 The pH of a solution can affect The The shapes and functions of shapes of molecules molecules The rates of many chemical rates of reactions reactions The ability of two molecules to bind bind to each other The ability of ions or molecules to dissolve in water dissolve
Organisms usually tolerate only small changes in pH changes Buffers help to keep a constant pH Buffers help constant An acid-base buffer system can shift An base to generate or release H+ to adjust for to to changes in pH changes 32 16 33 17 ...
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This note was uploaded on 05/18/2011 for the course BIOL 110 taught by Professor N/a during the Fall '08 term at University of Louisiana at Lafayette.
- Fall '08