Chapter 2 Chemical composition of the body Remon Wahba, MD

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

Atoms 2-3

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

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

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

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

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

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

Chemical Bonds 2-9

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

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

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

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

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

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

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

Ionic Bonds

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

Ionic Bonds

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

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.

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

Acids, Bases, & The pH Scale 2-17

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

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

Acids & Bases

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 7 - 14) 2-19

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

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

Organic Molecules 2-23

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

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

Organic Molecules continued Carbohydrates Lipids Proteins Nucleic Acids

Carbohydrates 2-28

Photosynthesis

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

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

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

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

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

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

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

Lipids 2-34

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

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

Fatty Acids 2-37

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

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

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

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

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

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

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

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

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

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

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

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

Proteins 2-43

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

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

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

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

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

Nucleic Acids 2-53

Nucleic Acids DNA Deoxyribonucleic Acid RNA Ribonucleic Acid

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

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

Deoxyribonucleic acid (DNA) 2-57

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

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

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

DNA & RNA