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Chapter 2 Chemical composition of the body Remon Wahba, MD Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 2 Outline Atoms Chemical Bonds Acids, Bases & the pH Scale Organic Molecules Carbohydrates Lipids Proteins Nucleic Acids Atoms 2-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atoms Smallest units of the chemical elements Composed of: Nucleus contains: Protons (+ charge) Neutrons (no charge) Electrons Shells: Electrons(- charge) 2-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atoms - Electron Shells Valence Electrons Electrons present in the outermost shell These can participate in chemical reactions & form bonds 2-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. electron shell Carbon (C) Oxygen (O) Phosphorus (P) Calcium (Ca) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Isotopes 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Types of Atoms There are 2 types of atoms: 1. Inert The outermost electron shell is completely full. 2. Reactive The outermost electron shell is partially full Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. electron nucleus Hydrogen (H) Helium (He) Chemical Bonds 2-9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Bonds Atoms unite together by Bonds Number of bonds determined by number of Electrons needed to complete (saturate) the outermost shell 2-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemical Bonds 1. Covalent Bonds Non-Polar Covalent Bonds Polar Covalent Bonds 2. Ionic Bonds 3. Hydrogen Bonds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Covalent Bonds when atoms Share valence electrons Occur Two Types: 1. Non-polar Covalent Bonds: 2. Polar Covalent Bonds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Covalent Bonds 1- Nonpolar Bonds: Electrons are shared equally between the two atoms E.g. in: H 2 02 Fig 2.2 2-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) nonpolar covalent bonding Hydrogen (H–H or H2), a nonpolar molecule Oxygen (O=O or O2), a nonpolar molecule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Covalent Bonds (continued) 2- Polar Covalent Bonds: Electrons are shared unequally Pulled more towards one atom Molecules Oxygen, Have (+) and (–) poles Nitrogen, Phosphorous have strong pull so tend to form polar molecules E.g. H20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (b) polar covalent bonding (slightly negative) (slightly positive) Water (H–O–H or H2O), a polar molecule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ionic Bonds 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ionic Bonds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ionic Bonds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hydrogen Bonds Forms between Adjacent H20 Molecules Create Surface Tension 2-16 Acids, Bases, & The pH Scale 2-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. water (H2O) hydroxide ion (OH – ) hydrogen ion (H+) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acids & Bases Acids: Release (H+) in a solution (proton donor) Bases: Absorb (H+) of a solution (proton acceptor) 2-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acids & Bases Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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+ + HC03This buffers pH because reaction can go in either direction depending upon concentration of H+s 2-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood pH Normal range of Blood pH is 7.35 Maintained – 7.45 by buffering action Acidosis occurs if pH < 7.35 Alkalosis occurs if pH > 7.45 2-22 Organic Molecules 2-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organic Molecules 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organic Molecules Carbohydrates Lipids Proteins Nucleic Acids continued Carbohydrates 2-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosynthesis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Carbohydrates Are organic molecules containing Carbon, Hydrogen & Oxygen in ratio of CnH2n0n Types: Monosaccharides Disaccharides Polysaccharides Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Monosaccharides Simple One sugars: molecule of Sugar Such as Glucose Fructose Galactose Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Polysaccharides Complex Carbohydrates Chains of Monosaccharides joined together by covalent bonds Starch In plants Glycogen In animals Stored in: Liver Skeletal Muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Formation of Disaccharides Occurs by removing water molecule out of Two Monosaccharides H+ & OH- are removed, producing H20 This is called Dehydration 2-32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Digestion of Polysaccharides 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 Occurs 2-33 Lipids 2-34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lipids Are insoluble in polar solvents such as water Hydrophobic Consist primarily of hydrocarbon Chains & Rings 2-35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Triglycerides Formed by condensation (Dehydration One Alcohol molecule (Glycerol) Three Fatty Acids There are 2 Types of Fatty Acids: Saturated Hydrocarbon chains of fatty Reaction) of: acids are joined by Single Covalent Bonds Unsaturated There are Double chains Bonds within the hydrocarbon Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fatty Acids 2-37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 One double bond alpha end Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Polyunsaturated Fatty Acid H H H H H H H H H H H HH 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 > 2 double bonds alpha end Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ketone Bodies 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ketosis & Ketoacidosis Occurs when the body depends of Fats as the main source of Energy In cases of: Severe Low un-controlled Diabetes Mellitus Carbohydrate Diets Starvation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ketosis & Ketoacidosis Ketone bodies can easily convert to Acetone which gives a Fruity smell to the breath Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phospholipids Are lipids that contain a Phosphate group The Plasma membrane that surrounds each cell is made up of double layer of Phospholipids Phosphate Lipid part is polar & Hydrophilic part is nonpolar & Hydrophobic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phospholipids Aggregate into Micelles in water Polar part interacts with water; nonpolar part is hidden in middle micelle Fig 2.21 Act as Surfactants by reducing surface tension (in the lungs) 2-40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Steroids Are Nonpolar & insoluble in water All have three 6carbon rings joined to a 5-carbon ring Fig 2.22 Cholesterol is: Precursor for steroid hormones Component of cell membranes 2-41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cholesterol Cholesterol is carried in the blood by 2 Lipoproteins: LDL ( Low Density Lipoproteins) Bad HDL ( High Density Lipoproteins) Good Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Prostaglandins Are Fatty Acids with cyclic hydrocarbon group Produced & active in most tissues Serve many Regulatory functions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Proteins Proteins are the building blocks of the body Important for the manufacture of hormones and enzymes Important Important for the production of antibodies for maintaining fluid and electrolyte balance of the body Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Proteins - Peptides Are short chains of amino acids Amino acids are linked by peptide bonds Formed by Dehydration reactions 2-45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Proteins - Peptides Two Amino Acids are called Dipeptide Three If <100 amino acids is called a Polypeptide; >100 A Amino Acids are called Tripeptide amino acids, is called a Protein typical protein contains about 1000 amino acids 2-46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleic Acids DNA Deoxyribonucleic Acid RNA Ribonucleic Acid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleic Acids Fig 2.29 Are made of long chains of Nucleotides. Each Nucleotide is made up of: Sugar Phosphate group Nitrogenous base Pyrimidines ( C & T) Purines (G & A) 2-54 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Deoxyribonucleic acid (DNA) 2-57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ribonucleic Acid (RNA) Consists of a long chain of nucleotides joined together by sugar-phosphate bonds Fig 2.32 Its Ribose sugar is bonded to 1 of 4 bases: Guanine or Adenine Cytosine or Uracil (replaces thymine) Single-stranded 2-58 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA and RNA DNA 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA & RNA