Chapter 2: The Chemistry of Life – Fundamental Principles for Anatomy & Physiology

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Atoms and Elements

Introduction to Chemistry in Anatomy & Physiology

Chemistry forms the foundation for understanding the structure and function of the human body. Atoms and elements are the building blocks of all matter, including biological tissues and fluids.

Atom: The smallest unit of matter that retains the properties of an element.
Element: A pure substance consisting of only one type of atom, distinguished by its atomic number.
Matter: Anything that has mass and occupies space.
Chemistry: The study of matter and its interactions.

Over 99.95% of an atom’s mass is located in its nucleus, which contains protons and neutrons. The number of protons equals the number of electrons, maintaining electrical neutrality, but the number of neutrons can vary.

Subatomic Particles

Proton: Positively charged particle found in the nucleus; mass ≈ 1 atomic mass unit (amu).
Neutron: Neutral particle found in the nucleus; mass ≈ 1 amu.
Electron: Negatively charged particle found in the electron cloud surrounding the nucleus; mass is negligible compared to protons and neutrons.

Major Elements in the Human Body

Four elements make up about 96% of the body’s mass: Oxygen (O) (65%), Carbon (C) (18%), Hydrogen (H) (10%), and Nitrogen (N) (3%).
Trace elements (e.g., iron, copper, iodine, zinc) are present in small amounts but are essential for physiological processes.
Minerals such as sodium, potassium, calcium, chlorine, magnesium, phosphorus, and sulfur are key inorganic components.

Atomic Number, Mass Number, Isotopes, and Radioisotopes

Atomic Number (Z): Number of protons in the nucleus; defines the element.
Mass Number (A): Total number of protons and neutrons in the nucleus.
Isotope: Atoms of the same element with different numbers of neutrons, resulting in different mass numbers.
Radioisotope: An unstable isotope that emits radiation as it decays to a more stable form.

Example: Hydrogen has three isotopes: protium (¹H), deuterium (²H), and tritium (³H).

Radioactivity: The process by which unstable nuclei lose energy by emitting radiation. Radioisotopes are used in medical imaging and cancer treatment.

Chemical Bonds and Molecules

Types of Chemical Bonds

Ionic Bond: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions (cations and anions) that attract each other.
Covalent Bond: Formed when two atoms share one or more pairs of electrons. Can be nonpolar (equal sharing) or polar (unequal sharing).
Hydrogen Bond: A weak attraction between a slightly positive hydrogen atom and a slightly negative atom (usually oxygen or nitrogen) in another molecule. Important for the structure of water, proteins, and DNA.

Molecules, Compounds, and Mixtures

Molecule: Two or more atoms chemically bonded together (e.g., O2, H2O).
Compound: A molecule containing atoms of different elements (e.g., NaCl, H2O).
Mixture: Physical combination of substances where each retains its own properties. Types include solutions, colloids, and suspensions.

Types of Mixtures

Type	Description	Example
Solution	Homogeneous mixture; solute particles are very small and do not settle out	Salt water, blood plasma
Colloid	Heterogeneous mixture; larger particles that do not settle out	Milk, cytosol
Suspension	Heterogeneous mixture; large particles that settle out over time	Blood (red blood cells in plasma)

Chemical Reactions and Energy

Types of Chemical Reactions

Synthesis (Anabolic) Reaction: Two or more reactants combine to form a larger, more complex product. Example:
Decomposition (Catabolic) Reaction: A reactant is broken down into simpler products. Example:
Exchange Reaction: Atoms or electrons are transferred between reactants. Example:
Oxidation-Reduction (Redox) Reaction: Involves the transfer of electrons; oxidation is loss of electrons, reduction is gain of electrons.

Energy in Chemical Reactions

Potential Energy: Stored energy, such as in chemical bonds.
Kinetic Energy: Energy of motion.
Endergonic Reaction: Requires input of energy; products have more energy than reactants.
Exergonic Reaction: Releases energy; products have less energy than reactants.
Activation Energy: Minimum energy required to start a chemical reaction.

Enzymes

Biological catalysts that speed up chemical reactions by lowering activation energy.
Highly specific for their substrates and reactions.
Not consumed or permanently altered in the reaction.

Water, Acids, Bases, and Salts

Properties of Water

High heat capacity and heat of vaporization.
Excellent solvent for polar and ionic substances ("like dissolves like").
Acts as a lubricant and cushion for body structures.

Acids, Bases, and pH

Acid: Proton (H+) donor; increases hydrogen ion concentration in solution.
Base: Proton acceptor; decreases hydrogen ion concentration.
Salt: Compound formed from the reaction of an acid and a base; dissociates into ions in water.
pH Scale: Measures hydrogen ion concentration;
pH 7 is neutral; below 7 is acidic; above 7 is basic (alkaline).

Buffers

Solutions that resist changes in pH by absorbing or releasing H+ ions.
Important biological buffers include bicarbonate, phosphate, and proteins.

Electrolytes

Substances that dissociate into ions in water and conduct electricity (e.g., NaCl, KCl).
Essential for nerve impulse transmission, muscle contraction, and fluid balance.

Organic Compounds: Carbohydrates, Lipids, Proteins, and Nucleic Acids

Monomers and Polymers

Monomer: Single subunit that can be bonded to form polymers.
Polymer: Large molecule made of repeating monomers.
Dehydration Synthesis: Anabolic reaction that joins monomers by removing water.
Hydrolysis: Catabolic reaction that breaks polymers into monomers by adding water.

Carbohydrates

Composed of C, H, and O in a 1:2:1 ratio.
Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose).
Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose).
Polysaccharides: Long chains of monosaccharides (e.g., glycogen, starch, cellulose).
Functions: Energy source, structural component.

Lipids

Composed of C, H, and O; hydrophobic and insoluble in water.
Fatty Acids: Saturated (no double bonds) or unsaturated (one or more double bonds).
Triglycerides: Glycerol + 3 fatty acids; energy storage, insulation, protection.
Phospholipids: Major component of cell membranes.
Steroids: Four-ring structure; includes cholesterol, hormones.
Eicosanoids: Regulatory molecules derived from fatty acids (e.g., prostaglandins).

Proteins

Composed of C, H, O, N (sometimes S); monomer is the amino acid.
Peptide Bond: Covalent bond between amino acids.
Levels of Structure: Primary (sequence), secondary (alpha-helix, beta-sheet), tertiary (3D folding), quaternary (multiple polypeptides).
Functions: Structure (keratin, collagen), transport, catalysis (enzymes), communication (hormones), movement (muscle proteins), protection (antibodies).
Denaturation: Loss of protein shape and function due to heat, pH, or chemicals.

Nucleic Acids

Composed of C, H, O, N, P; monomer is the nucleotide (nitrogenous base, pentose sugar, phosphate group).
DNA: Double-stranded; stores genetic information; bases: adenine, thymine, cytosine, guanine.
RNA: Single-stranded; involved in protein synthesis; bases: adenine, uracil, cytosine, guanine.
ATP (Adenosine Triphosphate): Main energy currency of the cell; hydrolysis releases energy for cellular processes.

Summary Table: Major Organic Compounds

Type	Building Blocks	Function	Examples
Carbohydrates	Monosaccharides	Energy source, structure	Glucose, glycogen, starch
Lipids	Fatty acids, glycerol	Energy storage, insulation, cell membranes	Triglycerides, phospholipids, steroids
Proteins	Amino acids	Structure, catalysis, transport, movement	Enzymes, antibodies, hemoglobin
Nucleic Acids	Nucleotides	Genetic information, protein synthesis	DNA, RNA, ATP