Chemistry and Chemical Reactions

Water Molecule Polarity and Hydrogen Bonds

  • Hydrogen atom: Slight positive charge.
  • Oxygen atom: Slight negative charge.
  • Hydrogen bonds form between water molecules due to attraction between the positive hydrogen and negative oxygen.
  • Hydrogen bonds are weak individually but collectively contribute to water's characteristics and create a stronger force.
  • Hydrogen bonds are constantly forming and breaking in liquid water.
  • When water freezes, hydrogen bonds lock in place, causing expansion.
  • All hydrogen bonds are broken when water vaporizes.
  • Hydrogen bonds slow evaporation and contribute to surface tension.

Chemical Reactions

  • Chemical reactions involve the forming or breaking of chemical bonds between atoms.
  • Reactants are substances that undergo rearrangement to form products.
  • Metabolism refers to all chemical reactions occurring in the human body at any given time.
  • Chemical reactions enable work, which is the movement of an object or change in the physical structure of matter.
  • Energy is the capacity to perform work.

Types of Energy

  • Kinetic Energy: Energy in motion.
    • Examples: skeletal muscle contraction, water flowing, electricity in a wire.
  • Potential Energy: Stored energy (also known as latent energy) that has the potential to do work.
    • Examples: food, gasoline.
  • Energy conversion is never 100% efficient; heat is always a byproduct.
  • Energy cannot be created or destroyed; it can only change forms.

Types of Chemical Reactions

  • Synthesis Reactions (Combination Reactions):
    • Smaller particles bond to form larger, more complex molecules.
    • A + B → AB
    • Involve bond formation; anabolic.
  • Decomposition Reactions:
    • Bonds within larger molecules are broken down.
    • Reverse of synthesis reactions; catabolic.
  • Exchange Reactions (Displacement Reactions):
    • Bonds are made and broken.
    • Notebook + worm → note + bookworm

Factors Influencing Reaction Rates

  • Most chemical reactions require an enzyme (a protein) to lower activation energy.
  • Factors influencing reaction rates:
    • Temperature.
    • Particle size.
    • Reactant concentration.
    • Presence of enzymes.
  • Enzymes lower activation energy, speeding up reactions.

Exergonic and Endergonic Reactions

  • Complex reactions in the body are often interlocked and controlled by specific enzymes.
  • Exergonic Reaction: Releases energy; catabolic.
  • Endergonic Reaction: Products contain more potential energy than reactants; anabolic.
  • Enzymatic reactions are necessary for processing metabolites (molecules synthesized or broken down in the body).

Organic vs. Inorganic Nutrients

  • Organic Nutrients:
    • Contain carbon and hydrogen.
    • Form structures like sugars, fats, proteins.
    • Generally formed through covalent bonds.
    • Major classes: carbohydrates, fats, proteins, nucleic acids.
  • Inorganic Nutrients:
    • Do not contain carbon.
    • Generally formed via ionic bonding.
    • Found in smaller amounts in living organisms.

Water: The Universal Solvent

  • Water dissolves substances due to its polar charges.
  • Body fluids contain many dissolved elements.
  • Polar Substances: Hydrophilic (water-loving).
  • Non-polar Molecules: Hydrophobic (water-fearing).

Electrolytes and pH Regulation

  • Body fluids contain electrolytes with important functions.
    • Examples: Sodium chloride (membrane potential), potassium, calcium (organ systems).
  • Water dissociation produces hydrogen ions (H+H^+) and hydroxide ions (OH−OH^-).
  • Maintaining proper pH is crucial for efficient chemical reactions.

The pH Scale

  • Ranges from 0 to 14.
  • Acids: 0 to just before 7.
  • Bases: Above 7 to 14.
  • Acids: Release hydrogen ions (H+H^+) in solution (proton donors); pH < 7.
    • Example: Hydrochloric acid (HCl).
  • Bases: Release hydroxide ions (OH−OH^-) in solution (proton acceptors).
    • Example: Sodium hydroxide (NaOH).
  • Salt: Electrolyte that dissociates to form ions; not reflected on the pH scale.
    • Example: Sodium chloride (NaCl).

Acids and Bases

  • Acid + Water → Releases H+H^+ ions.
  • Base + Water → Releases OH−OH^- ions.

Electrolytes and Buffers

  • Electrolytes are crucial for muscle contraction, nerve impulse conduction, blood clotting, bone development, etc.
  • Buffers resist changes in pH.
    • Release H+H^+ ions when pH rises.
    • Remove H+H^+ ions when pH falls.
    • Maintain constant pH.
  • Many buffers are weak acids with a salt of that acid.
    • Example: Carbonic acid and sodium bicarbonate.

Organic Compounds

  • Contain carbon; unique to living systems.
  • Many are polymers (chains of similar units or monomers).
  • Synthesized by dehydration synthesis; broken down by hydrolysis.
  • Often soluble in water; have specific functional groups.
  • Four major groups: carbohydrates, proteins, lipids, and nucleic acids.

Carbohydrates

  • Contain carbon, hydrogen, and oxygen in a 1:2:1 ratio (CH2OCH_2O).
  • Three classes: monosaccharides, disaccharides, polysaccharides.
  • Function: Major cell fuel (glucose); structural molecules (ribose).

Monosaccharides

  • Simple sugars: Three to seven carbon atoms.
  • Can be straight chains or rings.
    • Triose (3 carbons)
    • Pentose (5 carbons)
    • Hexose (6 carbons, e.g., glucose,fructose).
  • Examples: glucose, fructose, galactose, deoxyribose, ribose.
  • Isomers: Same molecular formula, different structure (e.g., glucose and fructose both have C<em>6H</em>12O6C<em>6H</em>{12}O_6).

Disaccharides

  • Two monosaccharides combined via dehydration synthesis (removal of water).
  • Too large to pass through cell membranes.
  • Broken down by hydrolysis (addition of water).
  • Sucrose (glucose + fructose) formed by dehydration synthesis.
  • Hydrolysis of sucrose yields glucose and fructose.

Polysaccharides

  • Polymers of simple sugars (eight or more monosaccharides).
  • Joined by dehydration synthesis.
  • Broken down by hydrolysis.
    • Starch (sugar storage in plants).
    • Glycogen (sugar storage in animals - liver and muscle cells).
    • Cellulose (indigestible to humans; in plant cell walls).

Lipids

  • Contain carbon, hydrogen, and oxygen; nonpolar and insoluble in water.
  • Less oxygen than carbohydrates; may contain phosphorus, nitrogen, or sulfur.
  • Examples: fats, oils, waxes.
  • Require special transport mechanisms in blood.
  • Functions: Cell component, energy reserve, chemical messengers, cell membrane formation.

Fatty Acids

  • Long chains with attached hydrogen atoms.
  • Head (COOH group): Hydrophilic.
  • Tail: Hydrophobic.

Saturated vs. Unsaturated Fatty Acids

  • Saturated Fatty Acids: No double bonds between carbons; maximum hydrogen atoms; solid animal fats (e.g., butter).
    • Implicated in increased risk of heart diseases.
  • Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature; plant oils (e.g., olive oil).

Glycerides

  • Lipids produced by dehydration synthesis between glycerol and fatty acids.
    • Monoglyceride: Glycerol + 1 fatty acid.
    • Diglyceride: Glycerol + 2 fatty acids.
    • Triglyceride: Glycerol + 3 fatty acids.
  • Function: Energy storage, insulation, protection.

Phospholipids and Glycolipids

  • Modified triglycerides with two fatty acid chains and a phosphorus-containing group.
  • Have hydrophilic heads and hydrophobic tails.
  • Important in cell membrane structure.

Steroids and Other Lipids

  • Steroids: Interlocking four-ring structures.
  • Cholesterol: Basis for all steroids in the body.
  • Leukotrienes: Produced by cells in response to injury or disease.
  • Prostaglandins: Released by cells to coordinate cellular activity.

Proteins

  • Contain carbon, oxygen, hydrogen, nitrogen, and sometimes sulfur or phosphorus.
  • Made from 20 different amino acids joined by peptide bonds.
  • Amino acids linked by removal of water; proteins broken down by insertion of water.
  • Amino acid structure: Amine group + variable side chain + carboxylic acid group.

Protein Structures

  • Dipeptide: Two amino acids.
  • Tripeptide: Three amino acids.
  • Polypeptide: Many amino acids (over 100 = protein).
  • Four Levels of Protein Structure:
    • Primary: Amino acid sequence.
    • Secondary: Coiled helix or pleated sheets with hydrogen bonds.
    • Tertiary: Folding exposing certain amino acids to the outside, held together by hydrogen bonds.
    • Quaternary: Combining of four or more proteins (not very common).
  • Fibrous Structural Proteins: Strand-like, water-insoluble, stable (e.g., collagen).
  • Globular Functional Proteins: Compact, spherical, water-soluble; have functional regions (e.g., heme unit).

Protein Denaturation

  • Breaks bonds holding folds and coils, changing shape.
  • Caused by heat, acid (pH change).
  • Reversible if conditions are restored quickly; irreversible if damage is beyond repair (e.g., cooking an egg).

Enzymes

  • Catalysts that speed up reactions in the body.
  • Specific enzyme for each reaction due to unique structure.
  • Substrates: Reactants in enzyme reactions.
  • Active Site: Region where enzyme binds substrate.
  • Enzymes lower the activation energy required to start a reaction.
  • Reaction Rates: Controlled by multiple enzymes with each under its own set of conditions.
  • Saturation Limit: Substrate concentration for maximum reaction rate.

Nucleic Acids: DNA, RNA, and ATP

  • Largest molecules in the body; contain carbon, oxygen, hydrogen, nitrogen, and phosphorus.
  • Building blocks: nucleotides.
    • Nitrogenous base, pentose sugar, and phosphate group.
  • DNA: Makes up genes; found in the nucleus and mitochondria.
  • RNA: Intermediate form for decoding DNA into protein.

Nucleotides

  • Phosphate group, pentose sugar (deoxyribose in DNA, ribose in RNA), and nitrogen base.
  • Nitrogen Bases:
    • Purines (double ring): Adenine (A), guanine (G).
    • Pyrimidines (single ring): Cytosine (C), thymine (T - in DNA), uracil (U - in RNA).
  • Nucleotides are linked via sugar-phosphate bonds to form long chains.
  • DNA: Double-stranded helix containing the instructions for protein synthesis.
  • RNA: Single-stranded molecule with uracil instead of thymine.

ATP: The Energy Currency

  • Adenine RNA nucleotides with two or three additional phosphate groups.
  • High-energy phosphate bonds are hydrolyzed to release energy.
  • All cells must have an available supply of ATP or they die.
    • AMP: Adenosine monophosphate (one phosphate).
    • ADP: Adenosine diphosphate (two phosphates).
    • ATP: Adenosine triphosphate (three phosphates).
  • ATP is synthesized constantly in every body cell.
  • Energy is the capacity to do work.