Introduction to Chemistry in Anatomy & Physiology

Chemistry forms the foundation for understanding the structure and function of the human body. This section covers the basic chemical principles essential for Anatomy & Physiology students, including matter, energy, atomic structure, chemical bonds, and the major classes of biological molecules.

Matter and Energy

• Matter: Anything that has mass and takes up space. Exists in four states: solid, liquid, gas, and plasma.

• Energy: The capacity to do work or cause change. Exists in several forms:

  • Kinetic energy: Energy of motion.

  • Potential energy: Stored energy due to position or structure.

  • Chemical energy: Stored in the bonds of chemical substances (e.g., ATP).

  • Electrical energy: Results from movement of charged particles (e.g., ions across cell membranes).

  • Mechanical energy: Directly involved in moving matter.

  • Radiant/electromagnetic energy: Travels in waves (e.g., visible light, X-rays).

Atoms and Elements

• Atom: The smallest unit of matter that retains the properties of an element.

• Subatomic particles:

  • Protons: Positively charged, found in the nucleus.

  • Neutrons: No charge, found in the nucleus.

  • Electrons: Negatively charged, orbit the nucleus.

• Atomic number: Number of protons in the nucleus; defines the element.

• Mass number: Sum of protons and neutrons.

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

• Ions: Atoms that have gained or lost electrons, becoming charged.

Elements in the Human Body

• 92 natural elements; about 25 are found in living organisms.

• Major elements: oxygen, carbon, hydrogen, nitrogen.

• Elements are organized in the periodic table by increasing atomic number.

Chemical Bonds and Compounds

Atoms combine to form molecules and compounds through chemical bonds, which determine the properties of substances in the body.

Types of Chemical Bonds

• Covalent bonds: Atoms share pairs of electrons. Can be nonpolar (equal sharing, e.g., CH4) or polar (unequal sharing, e.g., H2O).

• Ionic bonds: Formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions (e.g., NaCl).

• Hydrogen bonds: Weak attractions between a hydrogen atom carrying a partial positive charge and an electronegative atom (e.g., O or N). Important in water and biological molecules.

Mixtures and Solutions

• Mixtures: Physical combinations of two or more substances.

  • Solutions: Homogeneous mixtures; solute particles are very small and do not settle out (e.g., saline).

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

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

• Solvent: The substance doing the dissolving (usually water in biological systems).

• Solute: The substance being dissolved.

Water and Its Importance

• High heat capacity: Absorbs and releases heat slowly, helping maintain body temperature.

• High heat of vaporization: Requires large amounts of heat to evaporate, important for cooling (sweating).

• Polarity: Excellent solvent for ionic and polar substances.

• Chemical reactivity: Involved in hydrolysis and dehydration synthesis reactions.

• Cushioning: Protects organs from physical trauma (e.g., cerebrospinal fluid).

Acids, Bases, and Salts

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

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

• Salts: Ionic compounds that dissociate into ions in water; important electrolytes in the body (e.g., Na+, K+, Ca2+, Cl-).

• pH scale: Measures acidity or alkalinity of a solution.

  • pH 7 = neutral; below 7 = acidic; above 7 = basic (alkaline).

  • Each unit change represents a tenfold change in H+ concentration.

Organic Compounds

Organic compounds contain carbon and are essential to life. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

• Contain carbon, hydrogen, and oxygen (usually in a 1:2:1 ratio).

• Monosaccharides: Simple sugars (e.g., glucose, fructose, ribose, deoxyribose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose, maltose).

• Polysaccharides: Many monosaccharides linked (e.g., glycogen in animals, starch in plants, chitin in fungi and arthropods).

• Main function: Provide a readily available source of cellular fuel.

Lipids

• Contain carbon, hydrogen, and oxygen; may also contain phosphorus, nitrogen, or sulfur.

• Insoluble in water but soluble in nonpolar solvents.

• Triglycerides: Three fatty acids bonded to glycerol; main energy storage and insulation.

• Phospholipids: Two fatty acids and a phosphate group; major component of cell membranes.

• Steroids: Four interlocking hydrocarbon rings (e.g., cholesterol, hormones).

• Main functions: Energy storage, cell membrane structure, insulation, and hormone production.

Proteins

• Composed of amino acids (contain an amino group, carboxyl group, hydrogen, and R group).

• Levels of structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets formed by hydrogen bonding.

  • Tertiary: 3D folding due to side chain interactions.

  • Quaternary: Association of multiple polypeptide chains (e.g., hemoglobin).

• Functions:

  1. Structural (hair, skin, nails)

  2. Regulatory (hormones)

  3. Contractile (muscle proteins: actin, myosin)

  4. Transport (hemoglobin, membrane channels)

  5. Immunological (antibodies)

  6. Catalytic (enzymes)

Nucleic Acids

• Composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus.

• DNA: Double-stranded, stores genetic information, found in the nucleus.

• RNA: Single-stranded, involved in protein synthesis, found in the cytoplasm.

• ATP (adenosine triphosphate): The primary energy currency of the cell; energy is released by breaking high-energy phosphate bonds.

Summary Table: Major Classes of Biological Molecules

Key Equations

• Atomic mass:

• pH calculation: