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Chemical Composition of the Body

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  • 1. Chapter 2 Chemical Composition of the Body
  • 2. Objectives
    • Explain how covalent bonds are formed and distinguish between nonpolar and polar covalent bonds.
    • Describe the nature of hydrogen bonds and explain their significance.
    • Describe the structure of DNA and RNA, and explain the law of complementary base pairing.
  • 3. Chemical Bonds, Molecules, and Ionic Compounds
    • Chemical bonds:
      • Interaction of valence electrons between 2 or more atoms.
    • Number of bonds determined by number of electrons needed to complete outermost shell.
  • 4. Covalent Bonds
    • Atoms share their valence electrons.
    • Nonpolar covalent bonds:
      • Electrons are equally distributed between the two identical atoms.
      • Strongest bond.
        • H 2 and 0 2 .
    Figure 2.2
  • 5. Covalent Bonds (continued)
    • Polar bonds:
      • Electrons are shared between two different atoms.
        • Electrons may be pulled more toward one atom.
      • Has + and – poles.
      • Oxygen, nitrogen, phosphorous have tendency to pull electrons towards themselves.
    Figure 2.4
  • 6. Ionic Bonds
    • One or more valence electrons from one atom are completely transferred to a second atom.
    • Cation and anion attract, form ionic compound.
      • Weaker than polar covalent bonds.
    • Dissociate easily when dissolved in H 2 0.
      • Form hydration spheres.
    • Make an ion/molecule more soluble.
    • NaCl Na + + Cl -
    Figure 2.6 Figure 2.5
  • 7. Ionic Bonds (continued)
    • Glucose, amino acids, are H 2 0 soluble.
      • Hydration spheres form around atoms of oxygen, nitrogen, phosphorous.
        • Hydrophilic molecules.
    • Molecules composed of nonpolar covalent bonds are not H 2 0 soluble.
      • Cannot form hydration spheres.
        • Hydrophobic molecules.
  • 8. Hydrogen Bond
    • Hydrogen forms a polar bond with another atom, giving hydrogen has a slight + charge.
    • Weak attraction for a second electronegative atom.
      • Surface tension.
    Insert fig. 2.7 Figure 2.7
  • 9. Acid/Base
    • Acid:
      • Molecule that can release protons (H + ).
        • Proton donor.
    • Base:
      • Negatively charged ion that can combine with H + , and remove it from solution.
        • Proton acceptor.
  • 10. pH
    • pH = log _1__ [H + ]
      • [H + ] = molar concentration of H + .
      • pH inversely related to [H + ].
    • Because of logarithmic relationship, a solution with 10 times [H + ] of H 2 0 has a pH = 6; solution with 0.1 the [H + ] has a pH = 8.
  • 11. Organic MACROMolecules
    • Molecules that contain carbon and hydrogen.
    • Carbon has 4 electrons in outer shell and covalently bonds to fill its outer shell.
    • Functional groups:
      • Inactive “backbone” to which more reactive atoms are attached.
    • Carbonyl group:
      • Aldehydes and ketones.
    • Carboxyl group:
      • Organic acids (lactic and acetic acids).
    • Hydroxyl group:
      • Alcohol.
    Figure 2.10
  • 12. Carbohydrates
    • Organic molecules that contain carbon, hydrogen and oxygen.
      • C n H 2n 0 n .
    • Monosaccharides:
      • Simple sugars.
        • Glucose, fructose, galactose.
    • Disaccharide:
      • 2 monosaccharides joined covalently.
        • Sucrose (glucose and fructose), lactose (glucose and galactose), maltose (2 glucose).
    • Polysaccharide:
      • Numerous monosaccharides joined covalently.
        • Starch (thousands of glucose joined), glycogen (repeating glucose joined that are highly branched).
      • Mechanism for storing energy with less osmotic H 2 0 movement.
    Figure 2.13
  • 13. Lipids
    • Diverse group of molecules.
    • Differ greatly in chemical structure.
    • Insoluble in polar solvents (H 2 0).
    • Consist primarily of hydrocarbon chains and rings.
      • Hydrophobic.
  • 14. LIPIDS: Triglycerides (triacylglycerol)
    • Formed by condensation of glycerol and 3 fatty acids.
      • Fatty acids consist of nonpolar hydrocarbon chain with carboxyl end.
    • Saturated:
      • Hydrocarbon chains joined by single covalent bonds.
    • Unsaturated:
      • Double covalent bonds within hydrocarbon chain.
    Figure 2.17 Figure 2.18
  • 15. LIPIDS:Ketone Bodies
    • Hydrolysis of triglycerides in adipose tissue release free fatty acids.
      • Free fatty acids can be converted in the liver to ketone bodies.
    • Ketoacidosis:
      • Increased ketone bodies in the blood which lowers pH.
    Figure 2.19
  • 16. LIPIDS: Phospholipids
    • Phospholipids:
      • Number of different categories of lipids that contain phosphate group.
        • Nonpolar end is hydrophobic, polar end is hydrophilic.
      • Lecithin:
        • Phosphate attached to a nitrogen-containing choline molecule.
    Figure 2.20
  • 17. LIPIDS: Steroids
    • All have same basic structure; three 6-carbon rings joined to a 5-carbon ring.
      • Nonpolar and insoluble in H20.
    • Cholesterol is precursor for steroid hormones.
    Figure 2.22
  • 18. LIPIDS: Prostaglandins
      • Fatty acid with cyclic hydrocarbon group.
        • Derived from arachidonic acid.
      • Serve a variety of regulatory functions.
        • Blood vessel diameter, ovulation, uterine contractions, inflammation, blood clotting.
    Figure 2.23
  • 19. Proteins
    • Large molecules composed of long chains of amino acids.
      • 20 different amino acids can be used in constructing a given protein.
      • Each amino acid contains an amino group (NH2) at one end and carboxyl group (COOH) at the other end.
    • Differences between amino acids are due to differences in functional groups (“R”).
    Figure 2.24
  • 20. Protein Structure Level
    • Primary structure:
      • Sequence of the amino acids in the protein is described.
    • Secondary structure:
      • Weak hydrogen bonds form between hydrogen of 1 amino acid and the and oxygen of a different amino acid nearby.
        • a-helix or b-sheet.
    • Tertiary structure:
      • Polypeptide chains bend and fold to produce 3 -dimensional shape.
      • Formed and stabilized by weak chemical bonds between functional groups.
    • Quaternary structure:
      • Number of polypeptide chains covalently linked together.
    Figure 2.26
  • 21. Nucleic Acids
    • Include DNA and RNA.
    • Nucleotides:
      • Subunits of nucleic acids bonded together to form long polynucleotide chains.
        • Each composed of 3 smaller units:
          • 5-carbon sugar.
          • Phosphate group attached to one end of sugar.
          • Nitrogenous base attached to other end of sugar.
        • Nitrogenous bases:
          • Pyrimidines: single ring of carbon and nitrogen.
          • Purines: two rings of carbon and nitrogen.
    Figure 2.29
  • 22. NUCLEIC ACIDS: DNA and RNA
    • DNA:
    • Basis of genetic code.
    • Deoxyribose covalently bonded to 1 of 4 bases:
      • Purines: guanine and adenine.
      • Pyrimidines: cytosine and thymine.
      • Sugar-phosphate bonds form the chain.
    • Each base can form hydrogen bonds with other bases.
      • Two strands are are produced by hydrogen bonding.
    • RNA:
    • Consists of a single long chain of nucleotides joined together by sugar-phosphate bonds.
      • Ribose covalently bonds to 4 bases.
        • Uracil replaces thymine.
    Figure 2.32