Chapter 2: The Chemistry of Life

2.1 Atoms and Elements

This section introduces the basic building blocks of matter, focusing on the structure of atoms and the elements essential to human physiology.

• Subatomic Particles: Atoms are composed of protons (positive charge, mass ≈ 1 amu, located in the nucleus), neutrons (no charge, mass ≈ 1 amu, located in the nucleus), and electrons (negative charge, negligible mass, orbiting the nucleus).

• Atoms vs. Elements: An atom is the smallest unit of matter retaining the properties of an element. An element is a pure substance consisting of only one type of atom.

• Major Elements in the Human Body: The four most abundant elements are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

• Atomic Number, Mass Number, Isotopes, and Radioisotopes:

  • Atomic number: Number of protons in the nucleus.

  • Mass number: Sum of protons and neutrons.

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

  • Radioisotopes: Unstable isotopes that emit radiation as they decay.

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

2.2 Matter Combined: Mixtures and Chemical Bonds

This section explores how atoms combine to form mixtures and chemical bonds, which are fundamental to biological molecules.

• Types of Mixtures:

  • Suspensions: Large particles settle out (e.g., blood cells in plasma).

  • Colloids: Medium-sized particles remain dispersed (e.g., milk).

  • Solutions: Small particles dissolve completely (e.g., salt in water).

• Solvent vs. Solute: The solvent is the substance present in the greatest amount (usually water in the body), while the solute is 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 bonds.

• Molecule, Compound, and Ion:

  • Molecule: Two or more atoms bonded together (e.g., O2).

  • Compound: Molecule containing atoms of different elements (e.g., H2O).

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

• Chemical Bonds:

  • Ionic Bonds: Formed by transfer of electrons from one atom to another, creating charged ions (e.g., NaCl).

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

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

• Hydrogen Bonds and Surface Tension: Weak attractions between partially charged regions of polar molecules (e.g., between water molecules), responsible for water’s surface tension.

2.3 Chemical Reactions

Chemical reactions are processes in which chemical bonds are formed, broken, or rearranged, resulting in new substances.

• What Happens During a Chemical Reaction: Reactants are transformed into products by breaking and forming chemical bonds.

• Forms and Types of Energy:

  • Potential energy: Stored energy.

  • Kinetic energy: Energy of motion.

  • Chemical energy: Stored in chemical bonds.

  Endergonic reactions absorb energy; exergonic reactions release energy.

• Types of Chemical Reactions:

  • Synthesis (Anabolic) Reactions: Build larger molecules from smaller ones.

  • Decomposition (Catabolic) Reactions: Break down molecules.

  • Exchange Reactions: Atoms are exchanged between molecules.

• Factors Influencing Reaction Rates: Temperature, concentration, particle size, and presence of catalysts (e.g., enzymes).

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy, are highly specific, and are not consumed in the reaction.

2.4 Inorganic Compounds: Water, Acids, Bases, and Salts

Inorganic compounds are essential for physiological processes, with water being the most abundant and important.

• Properties of Water: High heat capacity, high heat of vaporization, excellent solvent, reactivity, and cushioning.

• Hydrophilic vs. Hydrophobic: Hydrophilic substances dissolve in water (polar/charged), while hydrophobic substances do not (nonpolar).

• Acids and Bases: Acids release hydrogen ions (H+), bases accept H+ or release hydroxide ions (OH-).

• pH Scale: Measures hydrogen ion concentration. pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic (alkaline).

• Buffers: Substances that minimize changes in pH by absorbing or releasing H+.

• Salts and Electrolytes: Salts dissociate into ions in water; electrolytes are ions that conduct electricity and are vital for nerve and muscle function (e.g., Na+, K+, Ca2+).

2.5 Organic Compounds: Carbohydrates, Lipids, Proteins, and Nucleotides

Organic compounds are carbon-based molecules essential for structure and function in living organisms.

• Monomers and Polymers: Monomers are single subunits; polymers are chains of monomers. Dehydration synthesis forms polymers by removing water; hydrolysis breaks polymers by adding water.

• Structures and Monomers:

  • Carbohydrates: Monomer = monosaccharide (e.g., glucose); polymer = polysaccharide (e.g., glycogen).

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

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

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

• Examples and Functions:

  • Carbohydrates: Energy source (glucose), energy storage (glycogen), structural (cellulose in plants).

  • Lipids: Energy storage (triglycerides), membrane structure (phospholipids), hormones (steroids).

  • Proteins: Enzymes, structural support (collagen), transport (hemoglobin), movement (actin, myosin).

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

• Protein Structure: Four levels:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets.

  • Tertiary: 3D folding of a single polypeptide.

  • Quaternary: Association of multiple polypeptides.

  Protein shape is critical for function; denaturation disrupts function.

• ATP Hydrolysis and Role: ATP (adenosine triphosphate) stores energy. Hydrolysis releases energy for cellular work: ATP is the primary energy currency of the cell.

Table: Comparison of Major Organic Molecules

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology textbooks.