1. CHEMISTRY PART 2

2. Chemical Bonds
Electron shells, or energy levels, surround the nucleus of an atom
Bonds are formed using the electrons in the outermost energy level
Valence shell – outermost energy level containing chemically active electrons
Octet rule – atoms usually react in a manner to have 8 electrons in their valence shell. (2 in first, 8 in second and third)

3. Chemically Inert and Reactive Elements
Inert elements have their outermost energy level fully occupied by electrons
Figure 2.4a

4. Chemically Inert and Reactive Elements
Reactive elements do not have their outermost energy level fully occupied by electrons
Figure 2.4b

5. Types of Chemical Bonds
Ionic
Covalent
Hydrogen

6. Ionic Bonds
Ions are charged atoms resulting from the gain or loss of electrons
Anions have gained one or more electrons
Cations have lost one or more electrons
Opposite charges on anions and cations hold them close together, forming ionic bonds

7. Formation of an Ionic Bond
Ionic compounds form crystals instead of individual molecules
Example: NaCl (sodium chloride)

8. Formation of an Ionic Bond
Figure 2.5

9. Covalent Bonds Electrons are shared by two atoms
Electron sharing produces molecules

10. Covalent Bonds
Figure 2.6a

11. Covalent Bonds
Figure 2.6b

12. Covalent Bonds
Figure 2.6c

13. Polar and Nonpolar Molecules
Electrons shared equally between atoms produce nonpolar molecules
Unequal sharing of electrons produces polar molecules
Atoms with 6 or 7 valence shell electrons are electronegative
Atoms with 1 or 2 valence shell electrons are electropositive

14. Comparison of Ionic, Polar Covalent, and Nonpolar Covalent Bonds
Figure 2.8

15. Hydrogen Bonds Too weak to bind atoms together
Common in dipoles such as water
Responsible for surface tension in water
Important as intramolecular bonds, giving the molecule a three-dimensional shape
Figure 2.9

16. Chemical Reactions
Occur when chemical bonds are formed, rearranged, or broken
Are written in symbolic form using chemical equations
Chemical equations contain:
Number and type of reacting substances, and products produced
Relative amounts of reactants and products
H + H  H2
(reactants) (product)

17. Patterns of Chemical Reactions
Combination reactions: Synthesis reactions which always involve bond formation
A + B  AB
Decomposition reactions: Molecules are broken down into smaller molecules
AB  A + B
Exchange reactions: Bonds are both made and broken
AB + C  AC + B

18. Oxidation-Reduction (Redox) Reactions
Reactants losing electrons are electron donors and are oxidized
Reactants taking up electrons are electron acceptors and become reduced

19. Energy Flow in Chemical Reactions
Exergonic reactions – reactions that release energy
Endergonic reactions – reactions whose products contain more potential energy than did its reactants

20. Reversibility of Chemical Reactions
All chemical reactions are theoretically reversible
A + B  AB
AB  A + B
If neither a forward nor reverse reaction is dominant, chemical equilibrium is reached

21. Factors Influencing Rate of Chemical Reactions
Temperature – chemical reactions proceed quicker at higher temperatures
Particle size – the smaller the particle the faster the chemical reaction
Concentration – higher reacting particle concentrations produce faster reactions
Catalysts – increase the rate of a reaction without being chemically changed
Enzymes – biological catalysts

22. Biochemistry Organic compounds Inorganic compounds
Contain carbon, are covalently bonded, and are often large
Inorganic compounds
Do not contain carbon
Water, salts, and many acids and bases

23. Water
High heat capacity – absorbs and releases large amounts of heat before changing temperature
High heat of vaporization – changing from a liquid to a gas requires large amounts of heat
Polar solvent properties – dissolves ionic substances, forms hydration layers around large charged molecules, and serves as the body’s major transport medium
Reactivity – is an important part of hydrolysis and dehydration synthesis reactions
Cushioning – resilient cushion around certain body organs

24. Salts Inorganic compounds
Contain cations other than H+ and anions other than OH–
Are electrolytes; they conduct electrical currents

25. Acids and Bases Acids release H+ and are therefore proton donors
HCl  H+ + Cl –
Bases release OH– and are proton receptors
NaOH  Na+ + OH–

26. Acid-Base Concentration (pH)
Acidic solutions have higher H+ concentration and therefore a lower pH
Alkaline solutions have lower H+ concentration and therefore a higher pH
Neutral solutions have equal H+ and OH– concentrations

27. Acid-Base Concentration (pH)
Acidic: pH 0–6.99
Basic: pH 7.01–14
Neutral: pH 7.00
Figure 2.12

28. Buffers
Systems that resist abrupt and large swings in the pH of body fluids
Carbonic acid–bicarbonate system
Carbonic acid dissociates reversibly releasing bicarbonate ions and protons
The chemical equilibrium between carbonic acid and bicarbonate resists pH changes in the blood

29. Break

30. Organic Compounds
Carbohydrates
Lipids
Proteins
Nucleic Acids

31. Carbohydrates Contain carbon, hydrogen, and oxygen
Their major function is to supply a source of cellular food
Examples:
Monosaccharides or simple sugars
Figure 2.13a

32. Carbohydrates
Disaccharides or double sugars
Figure 2.13b

33. Carbohydrates Polysaccharides or polymers of simple sugars
Figure 2.13c

34. Lipids
Contain C, H, and O, but the proportion of oxygen in lipids is less than in carbohydrates
Examples:
Neutral fats or triglycerides
Phospholipids
Steroids
Eicosanoids

35. Neutral Fats (Triglycerides)
Composed of three fatty acids bonded to a glycerol molecule
Figure 2.14a

36. Other Lipids
Phospholipids – modified triglycerides with two fatty acid groups and a phosphorus group
Figure 2.14b

37. Other Lipids
Steroids – flat molecules with four interlocking hydrocarbon rings
Eicosanoids – 20-carbon fatty acids found in cell membranes
Figure 2.14c

38. Representative Lipids Found in the Body
Neutral fats – found in subcutaneous tissue and around organs
Phospholipids – chief component of cell membranes
Steroids – cholesterol, bile salts, vitamin D, sex hormones, and adrenal cortical hormones
Fat-soluble vitamins – vitamins A, E, and K
Eicosanoids – prostaglandins, leukotriens, and thromboxanes
Lipoproteins – transport fatty acids and cholesterol in the bloodstream

39. Amino Acids
Building blocks of protein, containing an amino group and a carboxyl group
Amino acid structure
Figure 2.15

40. Protein
Macromolecules composed of combinations of 20 types of amino acids bound together with peptide bonds
Figure 2.16

41. Structural Levels of Proteins
Primary – amino acid sequence
Secondary – alpha helices or beta pleated sheets
Tertiary – superimposed folding of secondary structures
Quaternary – polypeptide chains linked together in a specific manner

42. Structural Levels of Proteins
Figure 2.17

43. Fibrous and Globular Proteins
Fibrous proteins
Extended and strandlike proteins
Examples: keratin, elastin, collagen, and certain contractile fibers
Globular proteins
Compact, spherical proteins with tertiary and quaternary structures
Examples: antibodies, hormones, and enzymes

44. Protein Denaturation
Reversible unfolding of proteins due to drops in pH and/or increased temperature
Figure 2.19a

45. Protein Denaturation
Irreversibly denatured proteins cannot refold and are formed by extreme pH or temperature changes
Figure 2.19b

46. Molecular Chaperones (Chaperonins)
Help other proteins to achieve their functional three-dimensional shape
Maintain folding integrity
Assist in translocation of proteins across membranes
Promote the breakdown of damaged or denatured proteins

47. Characteristics of Enzymes
Most are globular proteins that act as biological catalysts
Holoenzymes consist of an apoenzyme (protein) and a cofactor (usually an ion)
Enzymes are chemically specific
Frequently named for the type of reaction they catalyze
Enzyme names usually end in -ase
Lower activation energy

48. Characteristics of Enzymes
Figure 2.20

49. Mechanism of Enzyme Action
Enzyme binds with substrate
Product is formed at a lower activation energy
Product is released
Figure 2.21

50. Nucleic Acids
Composed of carbon, oxygen, hydrogen, nitrogen, and phosphorus
Their structural unit, the nucleotide, is composed of N-containing base, a pentose sugar, and a phosphate group
Five nitrogen bases contribute to nucleotide structure – adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U)
Two major classes – DNA and RNA

51. Deoxyribonucleic Acid (DNA)
Double-stranded helical molecule found in the nucleus of the cell
Replicates itself before the cell divides, ensuring genetic continuity
Provides instructions for protein synthesis

52. Structure of DNA
Figure 2.22a

53. Structure of DNA
Figure 2.22b

54. Ribonucleic Acid (RNA)
Single-stranded molecule found in both the nucleus and the cytoplasm of a cell
Uses the nitrogenous base uracil instead of thymine
Three varieties of RNA: messenger RNA, transfer RNA, and ribosomal RNA

55. Adenosine Triphosphate (ATP)
Source of immediately usable energy for the cell
Adenine-containing RNA nucleotide with three phosphate groups
Figure 2.23