The Chemistry of Life

Atoms and Elements

This section introduces the basic building blocks of matter, focusing on their structure and relevance to human physiology.

• Electrons, Protons, and Neutrons:

  • Protons: Positively charged, mass ≈ 1 amu, located in the nucleus.

  • Neutrons: No charge, mass ≈ 1 amu, located in the nucleus.

  • Electrons: Negatively charged, mass ≈ 1/1836 amu, orbit the nucleus in electron shells.

• Atoms vs. Elements:

  • Atom: Smallest unit of an element, retains chemical properties.

  • Element: Pure substance made of only one type of atom; cannot be broken down by ordinary chemical means.

• Major Elements in the Human Body:

  • Oxygen (O)

  • Carbon (C)

  • Hydrogen (H)

  • Nitrogen (N)

  These four elements make up over 96% of the body's mass.

• Atomic Number, Mass Number, Isotope, Radioisotope:

  • Atomic Number: Number of protons in the nucleus.

  • Mass Number: Sum of protons and neutrons.

  • Isotope: Atoms of the same element with different numbers of neutrons.

  • Radioisotope: Isotope with unstable nucleus; emits radiation as it decays.

• Production of Isotopes: Isotopes are produced naturally or artificially by altering the number of neutrons in an atom's nucleus.

Matter Combined: Mixtures and Chemical Bonds

This section explores how atoms combine to form mixtures and chemical bonds, which are essential for biological processes.

• Types of Mixtures:

  • Solutions: Homogeneous mixtures; solute particles are very small and evenly distributed (e.g., salt water).

  • Colloids: Heterogeneous mixtures; solute particles are larger but do not settle (e.g., milk).

  • Suspensions: Heterogeneous mixtures; solute particles are large and settle out (e.g., blood).

• Solvent vs. Solute:

  • Solvent: Substance present in greatest amount; dissolves the solute.

  • Solute: Substance dissolved in the solvent.

• Valence Electrons and Chemical Bonds: The number of electrons in the outermost shell (valence shell) determines an atom's stability and its ability to form chemical bonds.

• Molecule, Compound, Ion:

  • Molecule: Two or more atoms bonded together.

  • Compound: Molecule composed of two or more different elements.

  • Ion: Atom or molecule with a net electric charge due to loss or gain of electrons.

• Types of Chemical Bonds:

  • Ionic Bonds: Formed by transfer of electrons; results in oppositely charged ions (e.g., NaCl).

  • Nonpolar Covalent Bonds: Electrons shared equally between atoms (e.g., O2).

  • Polar Covalent Bonds: Electrons shared unequally, creating partial charges (e.g., H2O).

• Hydrogen Bonds and Surface Tension: Hydrogen bonds form between a hydrogen atom and an electronegative atom (like oxygen or nitrogen). In water, these bonds create surface tension, allowing small objects to rest on the surface.

Chemical Reactions

Chemical reactions are fundamental to life, enabling the transformation of substances and the release or absorption of energy.

• What Happens During a Chemical Reaction: Atoms are rearranged, bonds are broken and formed, resulting in new substances.

• Forms and Types of Energy:

  • Potential Energy: Stored energy.

  • Kinetic Energy: Energy of motion.

  Endergonic Reaction: Absorbs energy. Exergonic Reaction: Releases energy.

• Types of Chemical Reactions:

  • Synthesis: Two or more reactants combine to form a larger product.

  • Decomposition: A compound breaks down into smaller parts.

  • Exchange: Parts of reactants are exchanged.

• Factors Influencing Reaction Rates:

  • Temperature

  • Concentration of reactants

  • Particle size

  • Presence of catalysts

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy. Enzymes are essential for metabolic processes.

Inorganic Compounds: Water, Acids, Bases, and Salts

Inorganic compounds are vital for physiological functions, including water, acids, bases, and salts.

• Properties of Water:

  • High heat capacity

  • High heat of vaporization

  • Excellent solvent

  • Participates in chemical reactions

  • Cohesion and surface tension

• Hydrophilic vs. Hydrophobic:

  • Hydrophilic: Molecules attracted to water; dissolve easily (e.g., salts, sugars).

  • Hydrophobic: Molecules repel water; do not dissolve (e.g., oils, fats).

• Acids and Bases:

  • Acids: Release hydrogen ions (H+) in solution.

  • Bases: Accept hydrogen ions or release hydroxide ions (OH-).

• pH Scale: Measures hydrogen ion concentration. Scale ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

  • Acidic: pH < 7

  • Neutral: pH = 7

  • Basic: pH > 7

• Buffer: Substance that resists changes in pH by absorbing or releasing H+ ions.

• Salt and Electrolyte:

  • Salt: Ionic compound formed from acid and base reaction (e.g., NaCl).

  • Electrolyte: Substance that conducts electricity when dissolved in water; essential for nerve and muscle function.

Organic Compounds: Carbohydrates, Lipids, Proteins, and Nucleotides

Organic compounds are the basis of life, forming the structure and function of cells and tissues.

• Monomers and Polymers:

  • Monomer: Single building block (e.g., amino acid).

  • Polymer: Chain of monomers (e.g., protein).

  • Dehydration Synthesis: Joins monomers by removing water.

  • Hydrolysis: Breaks polymers into monomers by adding water.

• Structures and Monomers:

  • Carbohydrates: Monomer = monosaccharide; polymer = polysaccharide.

  • Lipids: Monomer = fatty acid; polymer = triglyceride, phospholipid, etc.

  • Proteins: Monomer = amino acid; polymer = polypeptide.

  • Nucleic Acids: Monomer = nucleotide; polymer = DNA or RNA.

• Examples and Roles:

  • Carbohydrates: Glucose (energy), glycogen (storage).

  • Lipids: Fats (energy storage), phospholipids (cell membranes), steroids (hormones).

  • Proteins: Enzymes, structural proteins (collagen), transport proteins (hemoglobin).

  • Nucleic Acids: DNA (genetic information), RNA (protein synthesis).

• Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helix or beta sheet (hydrogen bonding).

  • Tertiary: 3D folding due to interactions among side chains.

  • Quaternary: Multiple polypeptide chains joined.

  Protein shape determines function; misfolded proteins can cause disease.

• ATP Hydrolysis and Role:

  • ATP (adenosine triphosphate) is the cell's energy currency.

  • Hydrolysis reaction:

  • ATP provides energy for cellular processes.

Table: Comparison of Major Organic Molecules