1. Chapter 2 Chemical composition of the body
Remon Wahba, MD

2. Chapter 2 Outline Atoms Chemical Bonds Acids, Bases & the pH Scale
Organic Molecules
Carbohydrates
Lipids
Proteins
Nucleic Acids

3. Atoms
2-3

4. Atoms Smallest units of the chemical elements Composed of:
Nucleus contains:
Protons (+ charge)
Neutrons (no charge)
Electrons Shells:
Electrons(- charge)
2-4

5. Atoms continued Atomic mass is sum of protons & neutrons in an atom
Atomic number
is number of protons in an atom
is unique for every element
2-5

6. Electron Shells
Electron shells or Orbitals are in layers around the nucleus
Number of Electrons = Number of Protons
Number of shells depends on atomic number
First shell can have 2 Electrons only
Second shell can have up to 8 Electrons

7. Atoms - Electron Shells
Valence Electrons
Electrons present in the outermost shell
These can participate in chemical reactions & form bonds
2-7

9. Isotopes Contain same number of Protons
Are different forms of the Same Atoms
Contain same number of Protons
Contain different numbers of Neutrons
Atomic number is the same,
Atomic mass is different
2-8

10. Types of Atoms There are 2 types of atoms: Inert 2. Reactive
The outermost electron shell is completely full.
2. Reactive
The outermost electron shell is partially full

12. Chemical Bonds
2-9

13. Chemical Bonds Atoms unite together to form Molecules
Molecules form by chemical bonding between valence electrons of atoms
An Atom, with a partially full outermost electron shell is a Reactive atom
Atoms react with each other to Complete (Saturate) their outermost electron shell

14. Chemical Bonds Atoms unite together by Bonds
Number of bonds determined by number of Electrons needed to complete (saturate) the outermost shell
2-10

15. Chemical Bonds 1. Covalent Bonds Non-Polar Covalent Bonds
2. Ionic Bonds
3. Hydrogen Bonds

16. Covalent Bonds Occur when atoms Share valence electrons Two Types:
1. Non-polar Covalent Bonds:
2. Polar Covalent Bonds

17. Covalent Bonds
1- Nonpolar Bonds: Electrons are shared equally between the two atoms
E.g. in: H2 02
Fig 2.2
2-11

19. Covalent Bonds (continued)
2- Polar Covalent Bonds:
Electrons are shared unequally
Pulled more towards one atom
Molecules Have (+) and (–) poles
Oxygen, Nitrogen, Phosphorous have strong pull so tend to form polar molecules
E.g. H20

21. Ionic Bonds Bonds form by attraction of (+) & (-) charges
Occur when valence electrons are transferred from one atom to another; (Losing OR Gaining)
Forming charged atoms (ions)
An Atom that loses electrons becomes a Cation (+ charged )
An Atom that gains electrons becomes an Anion (- charged)
Bonds form by attraction of (+) & (-) charges

22. Ionic Bonds

23. Ionic Bonds Ionic bonds are weaker than Polar Covalent Bonds
Dissociate when dissolved in H20
Because H20 forms Hydration spheres around ions
E.g. NaCl

24. Ionic Bonds

25. Hydrophilic Vs. Hydrophobic
Hydrophilic molecules are Soluble in Water
Because readily form hydration spheres
E.g. glucose & amino acids
Hydrophobic molecules are nonpolar, cannot form hydration spheres (Insoluble in Water)
2-15

26. Hydrogen Bonds
Hydrogen Bonds form between Molecules with Polar Covalent Bonds
Water Molecules:
The negatively charged Oxygen atom attracts the positively charged hydrogen atoms of The Adjacent Molecules
Hydrogen bonds are weaker than Ionic and Covalent Bonds.

27. Hydrogen Bonds Forms between Adjacent H20 Molecules
Create Surface Tension
2-16

28. Acids, Bases, & The pH Scale
2-17

29. Acids and Bases
Water is very stable but few molecules constantly break into Ions
A Hydrogen ion ( H+ )
A Hydroxide Ion (OH- )
As the numbers of H+ and OH- are equal, water is considered Neutral

32. Acids & Bases Acids: Bases: Release (H+) in a solution (proton donor)
Absorb (H+) of a solution (proton acceptor)
2-18

33. Acids & Bases

34. Acids have a pH less than 7 (pH 0 - 7)
pH Scale
Is symbol for H+ concentration of a solution
pH scale runs from 0 to 14
Pure H20 is Neutral & has pH of 7
Acids have a pH less than 7 (pH 0 - 7)
Bases have a pH More than 7 (pH )
2-19

35. Buffers
Are molecules that prevent changes in pH by either combining with or releasing H+s
E.g. the Bicarbonate Buffer System in blood:
H20 + C02  H2C03  H+ + HC03-
This buffers pH because reaction can go in either direction depending upon concentration of H+s
2-21

36. Blood pH Normal range of Blood pH is 7.35 – 7.45
Maintained by buffering action
Acidosis occurs if pH < 7.35
Alkalosis occurs if pH > 7.45
2-22

37. Organic Molecules
2-23

38. Organic Molecules Carbon has 4 electrons in outer shell
Contain Carbon & Hydrogen
Carbon has 4 electrons in outer shell
Bonds Covalently to fill outer shell with 8 electrons
Carbon Serves as “Backbone” to which more reactive Functional groups are added
2-24

39. Organic Molecules continued
Functional groups:
Carbonyl group forms ketones & Aldehydes
Hydroxyl group forms Alcohols
Carboxyl group forms Organic Acids (Lactic & Acetic acids)
Fig 2.11
2-26

40. Organic Molecules continued
Carbohydrates
Lipids
Proteins
Nucleic Acids

41. Carbohydrates
2-28

42. Photosynthesis

43. Carbohydrates
Are organic molecules containing Carbon, Hydrogen & Oxygen in ratio of CnH2n0n
Types:
Monosaccharides
Disaccharides
Polysaccharides

44. Monosaccharides Simple sugars: One molecule of Sugar Such as Glucose
Fructose
Galactose

45. Disaccharides Disaccharides are 2 Monosaccharides joined covalently
Examples:
Sucrose (glucose + fructose) or Table Sugar
Lactose (glucose + galactose) or Milk Sugar
Maltose (2 glucoses) or Malt Sugar
2-30

46. Polysaccharides Liver Skeletal Muscles Complex Carbohydrates
Chains of Monosaccharides joined together by covalent bonds
Starch In plants
Glycogen In animals
Stored in:
Liver
Skeletal Muscles

47. Glycogen Stored in the Liver
Can be converted into Free Glucose which can be released into the blood stream to be used by All Body Cells as a source of energy
Stored in the Skeletal Muscles
Can be converted into Glucose 6 Phosphate which is trapped inside the muscle fibers to be used by the Skeletal Muscles Only to get energy

48. Formation of Disaccharides
Occurs by removing water molecule out of Two Monosaccharides
H+ & OH- are removed, producing H20
This is called Dehydration
2-32

49. Digestion of Polysaccharides
Occurs by Hydrolysis (reverse of dehydration)
H20 molecule is split and added, H+ added to one Monosaccharide, OH- to other
Polysaccharide are hydrolyzed into Disaccharides, then to Monosaccharides
2-33

50. Lipids
2-34

51. Lipids Hydrophobic Are insoluble in polar solvents such as water
Consist primarily of hydrocarbon Chains & Rings
2-35

52. Triglycerides Formed by condensation (Dehydration Reaction) of:
One Alcohol molecule (Glycerol)
Three Fatty Acids
There are 2 Types of Fatty Acids:
Saturated
Hydrocarbon chains of fatty acids are joined by Single Covalent Bonds
Unsaturated
There are Double Bonds within the hydrocarbon chains

53. Fatty Acids
2-37

54. Monounsaturated Fatty Acid
H H H H H H H H H H H H H H H O
H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
One double bond

55. Polyunsaturated Fatty Acid
H H H H H H H H H H H H H O
H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
> 2 double bonds

56. Ketone Bodies Ketoacidosis occurs when ketone bodies in blood lower pH
Hydrolysis of Triglycerides releases free fatty acids which can be either:
Used for energy
Converted in the Liver to ketone Bodies
High levels = ketosis
Ketoacidosis occurs when ketone bodies in blood lower pH

57. Ketosis & Ketoacidosis
Occurs when the body depends of Fats as the main source of Energy
In cases of:
Severe un-controlled Diabetes Mellitus
Low Carbohydrate Diets
Starvation

58. Ketosis & Ketoacidosis
Ketone bodies can easily convert to Acetone which gives a Fruity smell to the breath

59. Phospholipids Are lipids that contain a Phosphate group
The Plasma membrane that surrounds each cell is made up of double layer of Phospholipids
Phosphate part is polar & Hydrophilic
Lipid part is nonpolar & Hydrophobic

60. Phospholipids Aggregate into Micelles in water
Polar part interacts with water; nonpolar part is hidden in middle
Act as Surfactants by reducing surface tension (in the lungs)
micelle
Fig 2.21
2-40

61. Steroids Are Nonpolar & insoluble in water
All have three 6-carbon rings joined to a 5-carbon ring
Cholesterol is:
Precursor for steroid hormones
Component of cell membranes
Fig 2.22
2-41

62. Cholesterol Cholesterol is carried in the blood by 2 Lipoproteins:
LDL ( Low Density Lipoproteins) Bad
HDL ( High Density Lipoproteins) Good

63. Cholesterol, HDL & LDL Recommended Levels:
Total Cholesterol: Less than 200 mg / dL
HDL: Over 40 mg / 100ml
LDL: Less than 100 mg / 100ml
Triglycerides: Less than 100 mg /100ml 63

64. Prostaglandins Are Fatty Acids with cyclic hydrocarbon group
Produced & active in most tissues
Serve many Regulatory functions

65. Hydrogenation of Oils Adding Hydrogen to oil (hydrogenated oils)
Changing Unsaturated Fatty Acids into Saturated Fatty Acids
Oils become solid at room temperature (margarine)
To prolong the shelf-life of processed foods

66. Proteins
2-43

67. Proteins Proteins are the building blocks of the body
Important for the manufacture of hormones and enzymes
Important for the production of antibodies
Important for maintaining fluid and electrolyte balance of the body

68. Proteins - Amino Acids Are made of long chains of Amino Acids
There are 20 different amino acids
Two Types:
Essential:
Can not be produced inside our body
Nonessential:
Can be produced from other amino acids
2-44

69. Proteins - Peptides Are short chains of amino acids
Amino acids are linked by peptide bonds
Formed by Dehydration reactions
2-45

70. Proteins - Peptides Two Amino Acids are called Dipeptide
Three Amino Acids are called Tripeptide
If <100 amino acids is called a Polypeptide;
>100 amino acids, is called a Protein
A typical protein contains about 1000 amino acids
2-46

71. Protein - Structure Many proteins are conjugated with other groups
Glycoproteins
Contain Carbohydrates
Lipoproteins
Contain Lipids
Others proteins like Hemoglobin contain a pigment
2-52

72. Nucleic Acids
2-53

73. Nucleic Acids
DNA
Deoxyribonucleic Acid
RNA
Ribonucleic Acid

74. Nucleic Acids Are made of long chains of Nucleotides. Fig 2.29
Each Nucleotide is made up of:
Sugar
Phosphate group
Nitrogenous base
Pyrimidines ( C & T)
Purines (G & A)
Fig 2.29
2-54

75. Deoxyribonucleic acid (DNA)
Contains the Genetic code
Its Deoxyribose sugar (5C) is covalently bonded to 1 of 4 bases:
Guanine or Adenine (purines)
Cytosine or Thymine (pyrimidines)
Chain is formed by sugar of one nucleotide bonding to phosphate of another
Each base forms hydrogen bonds with other bases which holds 2 strands of DNA together
The 2 strands of DNA twist to form a Double Helix

76. Deoxyribonucleic acid (DNA)
2-57

77. Ribonucleic Acid (RNA)
Consists of a long chain of nucleotides joined together by sugar-phosphate bonds
Its Ribose sugar is bonded to 1 of 4 bases:
Guanine or Adenine
Cytosine or Uracil (replaces thymine)
Single-stranded
Fig 2.32
2-58

78. Ribonucleic Acid (RNA)
3 types of RNA are synthesized from DNA & allow it to direct activities of a cell:
Messenger RNA – mRNA
Transfer RNA – tRNA
Ribosomal RNA - rRNA
2-59

79. DNA and RNA DNA RNA Contains the sugar Deoxyribose
Contains Thymine instead of Uracil
Controls protein synthesis
Double Stranded
RNA
Contains the sugar Ribose
Contains the nitrogen base Uracil instead of Thymine
Carries the message from the nucleus to the cytoplasm to direct protein synthesis
Single stranded

80. DNA & RNA