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Chapter 2 The Chemical Level of Organization 2-1: Atoms • All matter is composed of elements – Atom—smallest unit of matter Atomic Structure • Atoms contain: – Protons (p+) – Neutrons (n0) – Electrons (e-) • Number of protons = atomic number 2-2 • Nucleus contains protons & neutrons – Electron cloud contains electrons in electron shells (levels) 2-3 Isotopes • Isotopes—neutron number differs • Protons + neutrons = mass number • Ex: carbon – C12: 6 protons, 6 neutrons – C13: 6 protons, 7 neutrons 2-4 Electron Shells • Atoms are neutral (protons = electrons) • Electrons occupy shells around nucleus – Unfilled shells make atom unstable • Shells: – 1st shell = 2 e– 2nd shell = 8 e2-5 2-6 2-1 Checkpoint 1. Define atom. 2. How is it possible for two samples of hydrogen to contain the same number of atoms but have different weights? 2-7 2-2: Chemical Bonds • Atoms become stable by combining through chemical bonds • Molecules—contain more than 1 atom – Ex: O2, H2 • Compound—2 or more elements bond – Ex: H2O, CO2, C6H12O6 2-8 Ionic Bonds • Add an electron = -1 charge (anion) Lose an electron = +1 charge (cation) • Ionic bonds—created when an anion & cation attract 2-9 2 - 10 Covalent Bonds • Covalent bond—electrons shared between elements • Single covalent bond—share 1 pair electrons • Double covalent bond—share 2 pairs of electrons 2 - 11 2 - 12 • Unequal sharing creates a polar covalent bond – One end slightly positive (δ+) – Other end slightly negative (δ-) 2 - 13 Hydrogen Bonds • Hydrogen bond—weak attraction between molecules • Positive end of one molecule attracts to negative end of another molecule • Important for DNA, water 2 - 14 2 - 15 2-2 Checkpoint 1. Define chemical bond, and identify several types of chemical bonds. 2. Why does oxygen combine readily with other elements, but neon does not? 3. Which kind of bond holds atoms in a water molecule together? What attracts water molecules to each other? 2 - 16 2-3: Chemical Reactions • Chemical reactions reactants products • Metabolism—all the chemical reactions in the body • Energy allows body to perform work 2 - 17 Types of Reactions • Decomposition reaction—molecules broken down AB A + B • Used in hydrolysis—breaks molecules to form water • Catabolism breaks down molecules in cells 2 - 18 • Synthesis reaction—molecules made A + B AB • Used in dehydration synthesis— breaks down water to form molecules • Anabolism forms new molecules in cells 2 - 19 • Exchange reaction—reacting molecules are shuffled AB + CD AD + CB Reversible Reactions • Many reactions are reversible A + B ↔ AB 2 - 20 2-3 Checkpoint 1. What is the molecular formula for glucose, with 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms? 2. Identify and describe three types of chemical reactions important to human physiology. 3. Glucose is converted into 2 threecarbon molecules. What type of 2 - 21 reaction is this? 2-4: Enzymes • Enzymes speed reactions in the body – Also called catalysts • Exergonic reactions release energy • Endergonic reactions require/absorb energy 2 - 22 2-4 Checkpoint 1. What is an enzyme? 2. Why are enzymes needed in our cells? 2 - 23 2-5: Inorganic & Organic Compounds • Inorganic compounds—molecules without both carbon & hydrogen – H2O, CO2, O2, acids, bases & salts • Organic compounds—contain both carbon & hydrogen – Carbs, lipids, proteins, nucleic acids 2 - 24 2-5 Checkpoint 1. Distinguish between inorganic compounds and organic compounds. 2 - 25 2-6: Water • Chemical reactions in body require water • Water has high heat capacity – Takes a lot of energy change temperature of water • Water dissolves & disperses many types of molecules 2 - 26 • Most chemical reactions occur in solutions – Contain fluid solvent & dissolved solutes • Ionic bonds broken apart by dissociation – Cations & anions mix with water 2 - 27 2-6 Checkpoint 1. List the chemical properties of water that make life possible. 2. Why does water resist changes in temperature? 2 - 28 2-7: Body Fluid pH • pH—concentration of hydrogen atoms – pH scale goes 0 – 14 • pH below 7 = acidic pH 7 = neutral pH above 7 = basic (alkaline) • pH of blood = 7.35 – 7.45 2 - 29 2 - 30 2-7 Checkpoint 1. Define pH, and explain how the pH scale relates to acidity and alkalinity. 2. Why is an extreme change in pH of body fluids undesirable? 2 - 31 2-8: Acids, Bases & Salts • Acid—substance that breaks apart & releases hydrogen ions HCl H+ + Cl- • Base—substance that removes hydrogen ions; frees a hydroxide (OH-) ion NaOH Na+ + OH2 - 32 Salts • Salt—break down in water, release cations & anions – Electrolytes—conduct electric currents Buffers & pH • Buffers—stabilize pH – Ex: antacids 2 - 33 2-8 Checkpoint 1. Define the following terms: acid, base, salt. 2. How does an antacid decrease stomach discomfort? 2 - 34 2-9: Carbohydrates • Carbohydrate—organic molecule with C, H, & O – Sugars & starches • Most important source of energy Monosaccharides • Simple sugars (glucose) • Can be a straight-chain or a ring 2 - 35 2 - 36 Disaccharides & Polysaccharides • Disaccharide—2 monosaccharides linked through dehydration synthesis – Monosacc. 1 + Monosacc. 2 Disacc. + H2O • Disaccharide split through hydrolysis – Disacc. + H2O Monosacc. 1 + Monosacc. 2 2 - 37 Dehydration Synthesis Hydrolysis 2 - 38 • Polysaccharide—chain of monosacc. – Starches—from plants – Cellulose—from cell walls of plants (fiber) – Glycogen—animal starch; chain of glucose molecules used as energy 2 - 39 2-9 Checkpoint 1. A food contains organic molecules with the elements C, H, and O. What class of compounds do these molecules represent, and what are their major functions in the body? 2. When two monosaccharides undergo a dehydration synthesis reaction, what type of molecule is formed? 2 - 40 2-10: Lipids • Lipid—organic molecule with C, H, & O – Fats, oils & waxes • Source of energy, forms cell structures Fatty Acids • Fatty acid—chain of carbon atoms 2 - 41 Fats • Glycerol + fatty acids fat – Triglyceride = glycerol & 3 fatty acids • Saturated fats – Fatty acid chains have single bonds (animal fats) • Unsaturated fats – Chains have double bonds (plant oils) 2 - 42 Steroids • Steroid—lipid molecule in rings • Cholesterol – Functions in cell membranes, hormones • Most cholesterol comes from diet 2 - 43 Phospholipids • Phospholipid—contains glycerol head & 2 fatty acid tails – Important in cell membranes • Head is hydrophilic, tails are hydrophobic 2 - 44 2 - 45 2-10 Checkpoint 1. Describe lipids. 2. Which kind of lipid would be found in a sample of fatty tissue taken from beneath the skin? 3. Which lipids would you find in human cell membranes? 2 - 46 2-11: Proteins • Protein—most abundant compound – Contain C, H, O, & N Protein Function • Many functions including: – Structural support – Movement & transport – Enzymes – Hormones – Defense (skin & nails) Protein Structure • Proteins composed of amino acids (a.a.) – 20 different a.a. in human body – a.a. determine protein function • Peptide bonds link a.a. into chains to form proteins 2 - 48 • a.a. sequence determines function – Incorrect a.a. can cause disfunction • Protein shape also determines function – Changes in temperature or pH causes denaturation—change in shape (irreparable) 2 - 49 2-11 Checkpoint 1. Describe a protein. 2. How does boiling a protein affect its structural and functional properties? 2 - 50 2-12: DNA & RNA • Nucleic acids—store & process genetic information – Contain C, H, O, N, & P • DNA determines inherited characteristics • RNA make proteins from DNA code 2 - 51 Structure of Nucleic Acids • Nucleic acids composed of nucleotides • Nucleotide structure – Phosphate – Sugar (deoxyribose or ribose) – Nitrogenous base: adenine (A), guanine (G), cytosine (C), thymine (T), uracil (U) 2 - 52 • DNA is a double helix of two strands – Complementary base pairs bond strands – A – T, G – C • RNA is a single strand 2 - 53 2 - 54 Compare DNA & RNA Sugar Strand Type Base Pairs Function 2 - 55 DNA deoxyribose double A, T, G, C genetic info RNA ribose single A, U, G, C protein synthesis 2-12 Checkpoint 1. Describe a nucleic acid. 2. A large organic molecule composed of ribose sugars, nitrogenous bases, and phosphate groups is which kind of nucleic acid? 2 - 56 2-13: ATP • Adenosine triphosphate (ATP)— most important high-energy compound • Adenosine diphosphate (ADP) combines with a phosphate to form ATP – Breakdown of ATP releases energy • ADP + phosphate + energy ↔ ATP + H2O 2 - 57 2-13 Checkpoint 1. Describe ATP. 2. What are the products of the breakdown of ATP? 2 - 58