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Chapter 2

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Chapter 2

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  1. Chapter 2 Chemical Composition of the Body

  2. Chapter 2 ObjectivesUnderstanding atoms, chemical bonds, organic molecules, and pH • Atoms • Chemical Bonds • pH Scale - acids and bases • Organic Molecules

  3. Periodic Table • 92 naturally occurring elements – basic building blocks of matter • A single unit of an element is the atom

  4. Human Body - 11 Elements

  5. Atoms • Atoms- smallest unit of the chemical elements - protons, neutrons, electrons • Nucleus - contains protons (+ charge) and neutrons (no charge) • Electrons (- charge) - occupy orbitals or shells outside of the nucleus • Isotypes - variant forms of an atom (neutons)

  6. Atomic Number • Number of protons in an atom

  7. Atomic Mass • Sum of protons and neutrons in an atom

  8. Periodic Table • Each element consists of one kind of atom - atom, the smallest unit of matter that still retains the properties of an element

  9. Atoms - Electron Shells • Electrons orbit the nucleus in electron shells or orbitals • Number of shells depends on atomic number • First shell can contain only 2 electrons • Second shell can contain up to 8 electrons • Electrons in more distant shells have higher energy • Valence electronsin the outermost incomplete shell - participate in chemical reactions and form bonds • Question – how many bonds can carbon form?

  10. Chemical Bonds • Molecules – formed by chemical bonding between valence electrons of 2 or more atoms • number of bonds are determined by the number of electrons needed to complete the outermost shell

  11. Nonpolar Covalent Bonds • Covalent bonds occur when atoms share valence electrons • Nonpolar covalent bonds - electrons are shared equally • e.g. in H2 or O2

  12. Polar Covalent Bonds • Electrons are shared unequally - pulled more toward one atom - have + and – poles - important for the basis of life • Oxygen, nitrogen, phosphorous – tend to form polar molecules - strong tendency to pull electrons toward themselves (electronegative) • Water – basic solvent of life for polar or charged molecules - hydrophilic - hydrophobic

  13. Properties of H2O

  14. Ionic Bonds • Valence electrons transferred from one atom to another • form charged atoms (ions) • Cation (+ charged ) - atom loses electrons - Na+ (natrium) • Anion (- charged) - atom gains electrons - Cl-

  15. Ionic Bonds – Hydration Spheres • Formed by attraction of + and – charges (opposites attract) • Weaker than polar covalent bonds • Dissociate when dissolved in H2O - H2O forms hydration spheres around ions - hydrophilic molecules (polar) soluble in water readily form hydration spheres (e.g. amino acids and glucose) - hydrophobic molecules (nonpolar) water insoluble cannot form hydration spheres

  16. Hydrogen Bonds • H forms a polar bond with another atom (eg. O, N, P) - H becomes slightly + • Hydrogen bonds- H+ attracted to nearby negatively charged atoms - relatively weak but plentiful - bond forms between adjacent H20s (surface tension)

  17. Class Exercise Molecules - Polar or Nonpolar?How many valence electrons?

  18. Acids, Bases and the pH Scale • Ionization of water - small proportion of polar covalent bonds in H20 break - the H electron is transferred to the oxygen - forms equals amounts of H+ (free proton) ions and OH- (hydroxide) ions • Acidic solution – higher H+ concentration than water • Basic solution – lower H+ concentration than water • Neutral solution – equal concentration of H+ and OH- • pH – potential of H+ - scale 0 to 14 based on log 1/[H+] or 10-0 to 10-14 - each step a 10-fold difference

  19. Acids and Bases • Acids release protons (H+) in a solution (proton donor) • Bases lower H+ levels of a solution (proton acceptor) • Litmus paper – changes color according to pH

  20. Buffers • System of molecules and ions that act to prevent changes in pH - either combine with or release H+s - stabilizes pH of a system because reaction can go in either direction depending on [H+] • Normal range of blood pH: 7.35 – 7.45 - maintained by buffering action of the bicarbonate buffer system H20 + C02 H2C03 H+ + HC03- (carbonic acid) (bicarbonate ion) • acidosis occurs if pH < 7.35 and alkalosis occurs if pH > 7.45

  21. Organic Molecules • Contain C and H • C has 4 valence electrons - covalently bond with other atoms

  22. Single and Double C Covalent Bonds

  23. Organic Molecules – Linear, Cyclic, or Aromatic • In the body Cs are linked to form chains or rings - serve as “backbone” to which more reactive functional groupsare added - functional groups usually contain O, N, P, or S

  24. Organic Molecules - Functional Groups • Organic molecules can be named according to their functional groups • Carbonyl group forms ketones and aldehydes • Hydroxyl group forms alcohols • Carboxyl group forms organic acids(lactic and acetic acids)

  25. Stereoisomers • Molecules may have the same atoms arranged in the same sequence - but differ in spatial orientation of a functional group • D-isomers (dextro) are right-handed • L-isomers (levo) are left-handed • Biological enzymes can act on only one of the stereoisomers - stereo-specific enzymes cannot combine with the wrong stereoisomer • Enzymes of all cells can use only L-amino acids and D-sugars

  26. Organic Molecules • “Large” organic molecules: Monomers - subunits of a macromolecule Polymers - chains of monomers bonded together Functional groups - clusters of atoms with a specific chemical property

  27. Carbohydrates • CnH2nOn - source of cellular energy - monosaccharides, disaccharides, polysaccharides • Monosaccharides- simple sugars - e.g. hexose sugars (glucose, fructose, galactose)

  28. Disaccharides • 2 monosaccharides joined by a covalent bond - sucrose or table sugar (=glucose + fructose) - lactose or milk sugar (=glucose + galactose) - maltose or malt sugar (=2 glucoses)

  29. Polysaccharides • Numerous monosaccharides linked together – energy storage molecules • starch and cellulose (plant) and glycogen(our body), 1000s of glucose monomers - organisms can store 1000s of glucoses in a single molecule drastically reducing osmotic problems

  30. Class Exercise Draw a monosaccharide, a disaccharide, and a polysaccharide

  31. Dehydration Synthesis (Condensation) • Reaction that links together monosaccharides in the formation of disaccharides and polysaccharides • H+ and OH- are removed producing H2O

  32. Hydrolysis - Digestion of Polysaccharides • Reverse of dehydration synthesis - a molecule of H2O is split - H+ added to one monosaccharide, OH- to the other • Polysaccharide - hydrolyzed into disaccharides  monosaccharides

  33. Lipids • Chemically diverse molecules with one common property - hydrophobic or insoluble in polar solvents such as water • Consist primarily of hydrocarbon chains and rings (nonpolar)

  34. Lipids - Triglycerides • Formed by condensation of glycerol (3-C OH) with 3 fatty acids (nonpolar hydrocarbon chain with a COOH) - includes fats and oils

  35. Triglycerides • Saturated - hydrocarbon chains of fatty acids joined by single covalent bonds (solid at room temperature) • Unsaturated - double bonds within the hydrocarbon chains (liquid at room temperature) “Which one do you prefer to have floating in your blood vessels”

  36. Cis and Trans Fatty Acids • Cis fatty acids - one c=c - hydrogens on the same side - configuration makes the fatty acid bend • Trans fatty acids - one c=c - partially hydrogenated vegetable oil (shortening) - hydrogens on opposite side - configuration makes the fatty acid straight

  37. Ketone Bodies • Hydrolysis of triglycerides releases free fatty acids - water soluble - used for energy or - converted in liver to ketone bodies • Ketone bodies are acidic - high levels cause ketosis - ketoacidosis occurs when ketone bodies in blood lower its pH - severe ketoacidosis (diabetes mellitus) may lead to coma and death

  38. Phospholipids • Lipids that contain a phosphate group • Phosphate part - polar and hydrophilic • Lipid part - nonpolar and hydrophobic - 2 fatty acid chains

  39. Phospholipids - Micelles • Phospholipids aggregate into micelles in water - polar part interacts with water - nonpolar part hidden in middle • Cell membrane – hydrophilic and hydrophobic “Why is this important” • Act as surfactants by reducing surface tension

  40. Steroids • Nonpolar - insoluble in water • All have three 6-carbon rings joined to a 5-carbon ring - can interconvert • Cholesterol - precursor for all steroid hormones - component of cell membranes

  41. Prostaglandins • Fatty acids with cyclic hydrocarbon group • Produced by and are active in most tissues • Serve many regulatory functions

  42. Class Exercise Draw the different categories of lipids

  43. Proteins • Composed of long chains of amino acids (>100) - 20 different amino acids - 8 essential amino acids • Amino acids (twitterion): Amino group(NH2) at one end Carboxyl group(COOH) at other end - differences due to functional groups (“R”)

  44. Polypeptide • Many monomers of amino acids bond together - amino acids linked by peptide bondsformed by dehydration reactions • Peptides - short chains of amino acids (<100)

  45. Protein Structure • Described at four levels - ‘structure reflects function’ - sensitive to temperature, pH, salts, prions • Primary structure - linear sequence of amino acids

  46. Secondary Structure • Formed by weak H bonding of amino acids: Alpha helix or Beta pleated sheet shapes

  47. Tertiary structure • Formed by bending and folding of polypeptide chains to produce 3-dimensional shape - formed and stabilized by weak bonds between functional groups - not very stable, can be denatured by heat, pH