The Chemical Level of Organization - Comprehensive Notes

I. General Chemistry

  • A. Energy and Matter
    • Matter: anything that has mass (weight) and takes up space; exists in three states: solid, liquid, gas.
    • Energy: capacity to do work or move something; all body activities are forms of work (e.g., breaking chemical bonds, building molecules, contracting a muscle).
    • Forms of energy:
    • Kinetic energy – energy in motion
    • Chemical energy – energy stored in chemical bonds
    • Electrical energy – energy from moving electric charges
    • All physiological processes involve energy transformations and work.
  • B. Chemical Elements
    • Element: a substance that cannot be broken down into simpler substances; built from atoms.
    • Four major elements forming the bulk of the body (approx. 96% of body weight):
    • Carbon (C)
    • Hydrogen (H)
    • Oxygen (O)
    • Nitrogen (N)
    • Other elements in the body (percentages approximate; listed to reflect typical teaching content):
    • Oxygen ~65% (by weight)
    • Carbon ~18–18.5%
    • Hydrogen ~9–10%
    • Nitrogen ~3–3.2%
    • Calcium ~1.5%
    • Phosphorus ~1.0%
    • Potassium ~0.4%
    • Sulfur ~0.3%
    • Sodium ~0.2%
    • Chlorine ~0.2%
    • Magnesium ~0.1%
    • Trace elements (examples): boron (B), chromium (Cr), cobalt (Co), copper (Cu), fluorine (F), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), zinc (Zn).
  • C. ATOMS
    • Atom: the basic unit of matter that can enter into a chemical reaction; composed of protons, neutrons, and electrons.
    • Atomic nucleus: located at the center; contains protons (positive) and neutrons (neutral).
    • Atomic number: number of protons in the nucleus; determines the identity of the element.
    • Electrons: negatively charged; located in electron shells/orbitals surrounding the nucleus.
    • Valence electrons: electrons in the outermost shell; determine bonding properties.
    • Octet Rule: atoms tend to end up with 8 valence electrons via gaining, losing, or sharing electrons during reactions.
  • D. Quick periodic context (conceptual)
    • Periodic table organizes elements by groups and periods; chemical properties largely depend on electron configuration and valence electrons.
    • Hydrogen (H) and Helium (He) exemplify the first period; elements in the same group share similar bonding behavior.
  • Did I Get This? (concept review)
    • Ninety-six percent of body weight is made up of .
    • Correct answer: D. Oxygen, carbon, hydrogen, nitrogen
    • Which subatomic particles are positively charged?
    • Protons

II. Inorganic Chemistry

  • A. Inorganic molecules
    • Inorganic molecules do not consist of carbon bonded to hydrogen; they may contain carbon or hydrogen, but not both in the same molecule (e.g., H2O, CO2).
  • B. Water: properties essential to life
    • Solvency: water’s polarity and V-shaped geometry enable dissolution of many substances (solvents). Water dissolves salts and polar molecules, forming aqueous solutions.
    • Cohesion: hydrogen bonding between water molecules creates surface tension and other cohesive properties.
    • Thermal stability: high heat capacity and high heat of vaporization help stabilize temperatures in organisms and environments.
  • 1. Solution concepts
    • Solution: liquid mixture of two or more substances.
    • Solvent: dissolving medium (water is the classic solvent in biology).
    • Solute: particles dissolved in the solvent (e.g., NaCl in water).
    • Aqueous solutions: uniform mixtures where the solvent is water.
  • 2. Hydration and dissociation
    • When salts dissolve, they often dissociate into ions (e.g., NaCl → Na⁺ + Cl⁻) with surrounding solvent molecules; salts are hydrophilic.
  • 4. Hydrophilic vs. Hydrophobic
    • Hydrophilic: water-loving; polar molecules and ions dissolve readily in water.
    • Lipophobic: tends not to dissolve fats.
    • Hydrophobic: water-fearing; nonpolar molecules do not dissolve in water (e.g., oils).
  • 5. pH and aqueous solutions
    • Pure water contains equal amounts of hydrogen ions (H⁺) and hydroxide ions (OH⁻).
    • Acids: dissociate to increase H⁺ concentration in solution.
    • Bases: dissociate to increase OH⁻ concentration in solution.
    • pH: scale 0–14 measuring hydrogen ion concentration; pH = -
      \,\log[H^+].
    • Acidic solutions: pH < 7 (more H⁺ than OH⁻).
    • Basic (alkaline) solutions: pH > 7 (more OH⁻ than H⁺).
    • Blood/ body fluids are normally near neutral to slightly alkaline (approx. pH 7.35–7.45 in blood; stomach is acidic).
  • 6. Buffers, salts, electrolytes, and homeostasis
    • Buffers: substances that resist pH changes by neutralizing added acids or bases (e.g., bicarbonate buffering system in blood).
    • Salts: ionic compounds that dissociate into cations and anions in water; many salts function as electrolytes.
    • Electrolytes: salts that conduct electrical signals in body fluids; essential for nerve function, muscle contraction, and hydration.
    • Homeostatic regulation of pH: maintained by breathing/ventilation, renal excretion, and buffers; normal blood pH ~ 7.35$-$7.45.
  • 7. Salts and Electrolytes overview
    • Salt: ionic compound that dissolves to form cations and anions.
    • Electrolyte: salt in bodily fluids that conducts electricity (e.g., Na⁺, K⁺, Cl⁻, HCO₃⁻).
  • 8. Quick review prompts
    • pH is a measure of hydrogen ion concentration; acidic solutions have more H⁺; basic solutions have more OH⁻.
    • Buffers help maintain pH by absorbing excess H⁺ or OH⁻.

III. Organic Chemistry

  • A. Organic molecules
    • Organic molecules contain carbon and hydrogen; oxygen and nitrogen are also common.
    • About 96% of body weight is CHON: Carbon, Hydrogen, Oxygen, Nitrogen.
    • Four major categories of carbon-containing compounds: Carbohydrates, Proteins, Lipids, Nucleotides/Nucleic acids.
  • B. Carbohydrates
    • General formula: CH2OCH_2O per unit; literally “carbon plus water.”
    • All carbohydrates are either simple sugars (monosaccharides) or polymers of sugars (polysaccharides).
    • Major functions: energy storage and ATP production.
    • Types:
    • Monosaccharides: single sugar molecules (e.g., glucose, fructose, galactose).
      • Glucose: subunit of most polysaccharides; found in blood.
      • Fructose: found in fruits, corn syrup.
      • Galactose: milk sugar.
      • Deoxyribose and ribose: sugars in DNA and RNA, respectively.
    • Disaccharides: two monosaccharides linked by dehydration synthesis; hydrolysis breaks them into monosaccharides.
      • Sucrose = glucose + fructose (table sugar)
      • Lactose = glucose + galactose (milk sugar)
      • Maltose = glucose + glucose
    • Polysaccharides: many monosaccharides joined together; storage or structural roles.
      • Starch: energy storage in plants (amylose, amylopectin components)
      • Glycogen: energy storage in animals (liver and muscle)
      • Cellulose: structural polysaccharide in plants; humans cannot digest; dietary fiber.
  • C. Lipids and Oils
    • Lipids are hydrophobic (insoluble in water).
    • Major types: fatty acids, triglycerides, phospholipids, steroids.
    • Fatty acids classification:
    • Saturated: all carbons saturated with hydrogen; single bonds; typically solid at room temperature; found mainly in animal products.
    • Unsaturated: one or more double bonds; kinks prevent tight packing; liquid at room temperature; found in plant oils.
    • Hydrogenated oils: partial hydrogenation converts some double bonds to single bonds, making the fat more solid and potentially generating free radicals that can damage tissues.
    • Triglycerides (neutral fats): three fatty acids attached to glycerol; most abundant lipid; stored in adipose tissue; main energy source.
    • Phospholipids: major components of cell membranes; amphipathic with hydrophobic tails and hydrophilic heads; form phospholipid bilayers.
    • Steroids and cholesterol: cholesterol is a steroid alcohol essential for cell membranes, steroid hormones, and bile synthesis; all steroids are derived from cholesterol; examples include testosterone, estrogen, estradiol, etc.
    • Prostaglandins: lipid-based signaling molecules derived from fatty acids; diverse roles in inflammation and physiology.
  • D. Proteins
    • Proteins are polymers of amino acids linked by peptide bonds.
    • Amino acids: central carbon with four groups attached – amino group (–NH₂), carboxyl group (–COOH), hydrogen, and a variable side chain (R).
    • 20 amino acids are used to build proteins; 9 are essential (must be obtained from the diet): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine.
    • The sequence of amino acids determines protein function.
    • Peptide bonds: link amino acids by joining the amino group of one amino acid to the carboxyl group of another.
    • Polypeptide: long chain of amino acids; proteins typically have 50+ amino acids.
    • Proteins are the most abundant organic compounds in the body and serve numerous structural and functional roles.
    • Protein structure levels:
    • Primary: amino acid sequence.
    • Secondary: alpha-helix or beta-pleated sheet.
    • Tertiary: further folding of secondary structures.
    • Quaternary: 3D arrangement of multiple polypeptide chains (e.g., hemoglobin).
    • Enzymes: biological catalysts, usually proteins, that speed up metabolic reactions by lowering activation energy; have specific substrates.
    • Metabolic pathways include catabolism (breaking down molecules) and anabolism (building larger molecules from smaller ones).
    • Structural proteins provide cohesion and support (e.g., elastin, keratin, actin/myosin).
    • Essential vs. nonessential amino acids:
    • 9 essential amino acids must be ingested; 11 can be synthesized by the body.
    • Proteins are generally hydrophilic in nature.
  • E. Nucleotides and Nucleic Acids
    • Nucleotides: building blocks of nucleic acids; consist of a phosphate group(s), a five-carbon sugar, and a nitrogenous base.
    • Nucleic acids: DNA and RNA.
    • DNA (deoxyribonucleic acid): stores genetic information; exists as a double helix in the nucleus; backbone made of sugar (deoxyribose) and phosphate; base pairs are formed by hydrogen bonds: Cytosine (C) with Guanine (G), and Adenine (A) with Thymine (T).
    • Base pairing: A−TA-T and C−GC-G
    • RNA (ribonucleic acid): single-stranded; sugar is ribose; bases: Cytosine (C), Guanine (G), Adenine (A), Uracil (U).
    • Types of RNA: Messenger RNA (mRNA), Ribosomal RNA (rRNA), Transfer RNA (tRNA).
    • ATP (Adenosine Triphosphate): the cell’s main energy currency; stores energy from exergonic reactions and releases it for cellular work; contains 3 phosphate groups; mitochondria generate ATP via cellular respiration.
  • Connections to physiology and real-world relevance
    • The chemical level of organization underpins how tissues and organs function: energy handling (ATP), membrane structure (phospholipids), signaling (prostaglandins, electrolytes, buffer systems), energy storage (glycogen, triglycerides), and genetic information (DNA/RNA).
    • Balance of acids and bases (pH) and buffering systems are essential for enzyme activity, metabolic reactions, and homeostasis.
    • Understanding bond types (ionic, covalent, hydrogen) helps explain molecular stability, enzyme-substrate interactions, and macromolecular structure (DNA, proteins, membranes).
  • Quick review prompts
    • Name the four major elements that make up about 96% of body weight.
    • What is the octet rule and why is it important for bonding?
    • Differentiate between hydrophilic and hydrophobic substances with examples.
    • What are the four structural levels of protein organization?
    • Identify the base pairs in DNA and the type of bond that holds them together.