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Chapter 7 THE CHEMISTRY OF LIFE
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A. Matter Material that takes up space. 1. Elements Pure chemical substances composed of atoms. F Examples? F How many elements exist? F How many of these elements are essential to life?
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Periodic Table of Elements
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2. Atom The smallest “piece” of an element that retains the characteristics of that element. Composed of 3 subatomic particles: F Protons F Neutrons F Electrons
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Characteristics of Subatomic Particles
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Atomic number # protons in nucleus of an atom (establishes identity of the atom) Since most atoms are electrically neutral, atomic number indicates # of electrons as well. Atomic mass # protons plus # neutrons in nucleus of an atom
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How can we determine the number of neutrons in an atom? # neutrons = atomic mass - atomic # ] Determine # neutrons in a carbon atom (atomic mass = 12; atomic # = 6). # neutrons = 12 - 6 = 6 Do all carbon atoms have the same number of protons? Do all carbon atoms have the same number of neutrons?
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Isotopes Atoms having the same number of protons, but differing numbers of neutrons. Ex. Carbon isotopes F carbon 12 ( 12 C) 6 neutrons F carbon 13 ( 13 C) 7 neutrons F carbon 14 ( 14 C) 8 neutrons
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Periodic table information on carbon: Atomic mass given in table is average mass of all the element’s isotopes.
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3. Compound A pure substance formed when atoms of different elements bond. The number of atoms of each element is written as a subscript. Examples: F CO 2 carbon dioxide F H 2 Owater F CH 4 methane F C 6 H 12 O 6 glucose
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4. Molecule Smallest piece of a compound that retains characteristics of that compound. The number of molecules is written as a coefficient. Examples: F 4CO 2 4 molecules of carbon dioxide F 2C 6 H 12 O 6 2 molecules of glucose F 6O 2 6 molecules of oxygen
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5. Chemical Bonds Type of bond formed is determined by the number of valence electrons in the interacting atoms [octet rule]. a) Covalent bonds - form when atoms share electron pairs. F strongest type of bond F tend to form when atoms have 3, 4 or 5 valence electrons F can be nonpolar or polar
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Nonpolar covalent bonds - electrons are shared equally between atoms. Ex. methane
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Polar covalent bonds - electrons are drawn more strongly to 1 atom’s nucleus than the other. Form when less electronegative atoms bond with more highly electronegative atoms. Ex. water
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b) Ionic bonds - form when oppositely charged ions are attracted to each other. F weaker than covalent bonds F atoms with 1, 2 or 3 valence electrons give up electrons to atoms with 7, 6 or 5 valence electrons F form salts Ex. NaCl
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c) Hydrogen bonds - form when opposite charges on two molecules are attracted to each other. F weakest type of bond* Ex. DNA H2OH2O
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B. The Importance of Water 1. Properties ] Cohesion - the attraction of water molecules for each other. ] Adhesion - the attraction of water molecules for other compounds. ] High heat capacity – takes a great deal of heat to raise the temperature of water.
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] High heat of vaporization - a lot of heat is required to evaporate water. ] Exists as solid, liquid or gas - solid (ice) is less dense than liquid. 2. Solutions A solution is a mixture of one or more solutes dissolved in a solvent. If solvent is water, then it is an aqueous solution. Water is a strong solvent because it separates charged atoms or molecules.
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3. Acids & Bases ] Acids - substances that add H + to a solution. ] Bases - substances that remove H + from solution. pH scale is measure of acidity/alkalinity based on H + concentration.
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C. Major Organic Molecules Molecules that contain carbon in combination with hydrogen. 1. Carbohydrates F contain C, H & O [ C O] F function to store energy & provide support F building blocks (monomers) are monosaccharides
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Monosaccharides F simple sugars containing 3 - 7 carbons. F C, H, O ratio is 1:2:1
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Disaccharides F simple sugars composed of 2 monosaccharides linked together by dehydration synthesis. Other common disaccharides: maltose (seed sugar) & lactose (milk sugar).
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Polysaccharides F complex carbohydrates made up of hundreds of monomers linked by dehydration synthesis.
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2. Lipids F contain C, H, O [ C >> O] F do not dissolve in water Triglycerides (fats) F composed of glycerol linked to 3 fatty acid chains by dehydration synthesis. F function to cushion organs, as insulation & in long-term energy storage (adipose tissue).
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Phospholipids F lipid bonded to a phosphate group F major component of cell membranes
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Sterols F lipids that have 4 interconnected carbon rings Ex. Vitamin D, cortisone, estrogen & cholesterol Waxes F fatty acids combined with hydrocarbons F help waterproof fur, feathers, leaves & fruits
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3. Proteins F contain C, H, O, N, (S) F monomers are amino acids
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Proteins have a 3-dimensional shape (conformation) : ] primary (1 o ) structure - amino acid sequence of polypeptide chain ] secondary (2 o ) structure - coiling & folding produced by hydrogen bonds ] tertiary (3 o ) structure - shape created by interactions between R groups ] quarternary (4 o ) structure - shape created by interactions between two or more polypeptides
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Examples: F antibodies F hemoglobin F insulin & glucagon F keratin F fibrin & thrombin F spider silk (strongest natural fiber known) F enzymes (maltase, pepsin, lipase)
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4. Nucleic Acids F contain C, H, O, N, P F monomers are nucleotides
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DNA (deoxyribonucleic acid) F 5-carbon sugar is deoxyribose F nitrogenous bases are A, G, C & T F double-stranded helix held together by hydrogen bonds F is the genetic material
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RNA (ribonucleic acid) F 5-carbon sugar is ribose F nitrogenous bases are A, G, C & U F single-stranded F enables information in DNA to be expressed
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