Chapter 2: Chemistry Comes Alive

Background Terminology

Understanding basic chemical concepts is essential for studying Anatomy & Physiology, as the human body is composed of matter and energy. Matter exists in different states, and energy is required for bodily functions.

• Matter: Anything that occupies space and has mass.

• States of Matter:

  • Solid: Definite shape and volume.

  • Liquid: Definite volume, no definite shape.

  • Gas: No definite shape or volume.

• Energy: The capacity to do work or put matter into motion.

  • Kinetic Energy: Energy in action.

  • Potential Energy: Stored energy, capable of doing work.

• Forms of Energy:

  • Chemical: Stored in chemical bonds (e.g., food, ATP).

  • Electrical: Movement of charged particles.

  • Mechanical: Directly involved in moving matter.

  • Radiant: Travels in waves (electromagnetic spectrum).

Basic Atomic Structure

Atoms are the fundamental units of elements, which make up all matter. Their structure determines their chemical properties and interactions.

• Element: Unique substance that cannot be broken down by ordinary chemical methods; listed in the periodic table.

• Atom: Smallest unit of an element, composed of subatomic particles:

  • Protons: Positively charged, found in nucleus.

  • Neutrons: Neutral, found in nucleus.

  • Electrons: Negatively charged, orbit nucleus in electron cloud.

• Atomic Number: Number of protons in an element; written as a subscript to the left of the atomic symbol.

• Physical Properties: Observable/measurable (color, texture, boiling point).

• Chemical Properties: Describe how atoms react with other atoms.

Major Elements, Minerals, and Trace Elements of the Body

The human body is primarily composed of four major elements, with additional minerals and trace elements essential for physiological functions.

• Major Elements (≈96% of body weight): Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N).

• Minerals: Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg), Iodine (I), Iron (Fe).

• Trace Elements: Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn).

Example: Calcium is essential for bone structure and muscle contraction; Iron is crucial for oxygen transport in hemoglobin.

Definitions: Molecule, Compound, Mixture, Solution, Solvent, Solute

Understanding these terms is fundamental for describing chemical interactions in the body.

• Molecule: Combination of two or more atoms held together by chemical bonds. Example: H2 (hydrogen gas).

• Compound: Molecule formed from two or more different kinds of atoms; chemically pure, all molecules identical. Example: H2O (water).

• Mixture: Two or more substances physically intermixed. Example: Air.

• Solution: Homogeneous mixture of components (gas, liquid, or solid). Example: Seawater.

• Solvent: Substance present in greatest amount in a solution; dissolving medium. Example: Water.

• Solute: Substance present in smaller amounts; dissolved in solvent. Example: Salt in water.

Chemical Bonds: Ionic, Covalent, Hydrogen

Chemical bonds are essential for the structure and function of molecules in the body. The type of bond affects molecular properties and biological activity.

• Ionic Bond: Formed by transfer of electrons from one atom to another, resulting in ions (charged atoms). Example: Sodium chloride (NaCl).

• Covalent Bond: Formed by sharing electrons between atoms.

  • Nonpolar Covalent: Electrons shared equally. Example: H2.

  • Polar Covalent: Electrons shared unequally due to electronegativity. Example: H2O.

• Hydrogen Bond: Weak bond between a hydrogen atom (already covalently linked) and another electronegative atom (O or N). Important for water cohesion and stabilization of proteins/DNA.

Example: Hydrogen bonds stabilize the double helix structure of DNA.

Patterns of Chemical Reactions

• Synthesis (Anabolic): Constructive, absorbs energy (endergonic).

• Decomposition (Catabolic): Breaks down molecules, releases energy (exergonic).

• Exchange: Bonds are broken and re-formed to make new compounds.

• Catalyst: Substance that speeds up reactions without being changed; enzymes are biological catalysts.

Water: Inorganic Compound and Universal Solvent

Water is the most abundant inorganic compound in the body and is essential for life due to its unique properties.

• High Heat Capacity: Absorbs/releases large amounts of heat, stabilizing body temperature.

• High Heat of Vaporization: Requires much heat to evaporate, enabling cooling via perspiration.

• Polar Solvent Properties: Dissolves ionic and polar substances; forms hydration layers around charged molecules.

• Reactivity: Participates in hydrolysis (decomposition) and dehydration synthesis (assembly).

Example: Water dissolves salts and nutrients, facilitating transport and chemical reactions in the body.

pH Scale, Buffers, Acids, and Bases

The pH scale measures the concentration of hydrogen ions in solutions, which is critical for maintaining homeostasis in the body.

• Acid: Releases hydrogen ions (H+); example: Hydrochloric acid (HCl) in the stomach.

• Base: Takes up hydrogen ions; characterized by hydroxyl ions (OH-); example: Bicarbonate ion.

• pH Scale: Ranges from 0 (acidic) to 14 (basic); 7 is neutral. Each unit represents a ten-fold change in H+ concentration.

• Blood pH: Must be maintained between 7.35 and 7.45.

• Buffer: Substance that prevents large shifts in pH by releasing or binding H+ ions.

Example: Buffers in blood prevent acidosis or alkalosis, maintaining physiological function.

Formula:

Biological Macromolecules: Carbohydrates, Proteins, Lipids, Nucleic Acids

Macromolecules are essential for structure and function in the body. Each class has unique properties and roles.

• Carbohydrates: Sugars and starches; composed of C, H, O.

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

  • Disaccharides: Two sugar units (e.g., sucrose).

  • Polysaccharides: Many sugar units (e.g., starch, glycogen).

  • Function: Primary source of cellular fuel.

• Lipids: Insoluble in water; include fats, phospholipids, steroids.

  • Triglycerides: Glycerol + 3 fatty acids; energy storage.

  • Phospholipids: Glycerol + 2 fatty acids + phosphate; major component of cell membranes.

  • Steroids: Four interlocking rings; example: cholesterol (precursor for hormones, vitamin D).

  • Function: Energy storage, membrane structure, hormone synthesis.

• Proteins: Chains of amino acids joined by peptide bonds.

  • Fibrous Proteins: Structural (e.g., collagen).

  • Globular Proteins: Functional (e.g., enzymes, hormones).

  • Enzymes: Biological catalysts; accelerate reactions without being consumed.

  • Function: Structure, catalysis, regulation.

• Nucleic Acids: DNA and RNA; composed of nucleotides (phosphate, sugar, nitrogen base).

  • DNA: Genetic material; contains genes for protein synthesis.

  • RNA: Assists in gene expression; carries code for protein synthesis.

  • ATP: Energy carrier molecule.

Example: Glycogen is the storage form of carbohydrate in animal tissues; enzymes regulate metabolic reactions.

Summary Table: Major Elements, Minerals, and Trace Elements

Additional info: Table entries inferred for clarity and completeness.