Chapter 2: Chemistry Comes Alive

Introduction

Chemistry is fundamental to understanding all physiological processes in the human body. This chapter explores the basic principles of chemistry and biochemistry, which are essential for comprehending how the body functions at the molecular and cellular levels.

2.1 Matter and Energy

Matter

• Matter is anything that has mass and occupies space. It can be seen, smelled, or felt.

• Weight is the measure of mass plus the effects of gravity.

• States of matter:

  • Solid: Definite shape and volume.

  • Liquid: Changeable shape, definite volume.

  • Gas: Changeable shape and volume.

Energy

• Energy is the capacity to do work or put matter into motion.

• Exists in two forms:

  • Kinetic energy: Energy in action.

  • Potential energy: Stored (inactive) energy.

• Forms of energy:

  • Chemical energy: Stored in bonds of chemical substances.

  • Electrical energy: Results from movement of charged particles.

  • Mechanical energy: Directly involved in moving matter.

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

• Energy conversions are inefficient; some energy is lost as heat.

2.2 Atoms and Elements

Elements

• Elements are substances that cannot be broken down into simpler substances by ordinary chemical methods.

• Four elements make up 96% of the human body: carbon, oxygen, hydrogen, and nitrogen.

• Atoms are the unique building blocks of each element, giving elements their physical and chemical properties.

Structure of Atoms

• Atoms are composed of three subatomic particles:

  • Protons: Positive charge, 1 atomic mass unit (amu).

  • Neutrons: No charge, 1 amu.

  • Electrons: Negative charge, virtually no mass.

2.3 Combining Matter

Molecules and Compounds

• Molecule: Two or more atoms bonded together.

• Compound: Molecule with two or more different kinds of atoms bonded together.

Mixtures

• Most matter exists as mixtures: two or more components physically intermixed.

• Three basic types:

  • Solutions: Homogeneous mixtures; solute particles are very tiny and do not settle out or scatter light.

  • Colloids: Heterogeneous mixtures; solute particles are larger than in solutions and scatter light but do not settle out.

  • Suspensions: Heterogeneous mixtures; solute particles are very large, settle out, and may scatter light.

2.4 Chemical Bonds

Role of Electrons in Chemical Bonding

• Electrons in the outermost shell (valence shell) are involved in chemical reactions.

• Atoms achieve stability by gaining, losing, or sharing electrons to fill their valence shell (usually 8 electrons).

Chemically Inert and Reactive Elements

• Chemically inert elements have full valence shells and are stable (e.g., helium, neon).

• Chemically reactive elements have incomplete valence shells and tend to gain, lose, or share electrons (e.g., hydrogen, carbon, oxygen, sodium).

Types of Chemical Bonds

• Ionic bonds: Involve transfer of electrons from one atom to another, resulting in ions (cations and anions). Opposite charges attract.

• Covalent bonds: Involve sharing of two or more valence electrons between atoms. Can be single, double, or triple bonds.

• Hydrogen bonds: Weak attractions between electropositive hydrogen and electronegative atoms (e.g., oxygen, nitrogen).

Formation of Ionic Bonds

Formation of Covalent Bonds

Polar and Nonpolar Covalent Bonds

• Nonpolar covalent bonds: Equal sharing of electrons; electrically balanced molecules (e.g., O2, CO2).

• Polar covalent bonds: Unequal sharing of electrons; results in molecules with partial charges (e.g., H2O).

2.5 Types of Chemical Reactions

• Synthesis (combination) reactions: Atoms or molecules combine to form larger, more complex molecules. Used in anabolic processes.

• Decomposition reactions: Breakdown of a molecule into smaller molecules or atoms. Involve catabolic processes.

• Exchange (displacement) reactions: Involve both synthesis and decomposition; bonds are both made and broken.

• Exergonic reactions: Release energy; products have less potential energy than reactants.

• Endergonic reactions: Absorb energy; products have more potential energy than reactants.

Factors Affecting Reaction Rates

• Temperature: Higher temperature increases reaction rate.

• Concentration: Higher concentration increases reaction rate.

• Particle size: Smaller particles increase reaction rate.

• Catalysts (including enzymes) increase reaction rate without being consumed.

Part 2—Biochemistry

Inorganic and Organic Compounds

• Inorganic compounds: Water, salts, acids, and bases; do not contain carbon (with some exceptions).

• Organic compounds: Carbohydrates, lipids, proteins, nucleic acids; contain carbon and are usually large and covalently bonded.

2.6 Inorganic Compounds

Water

• Most abundant inorganic compound in the body (60–80% of cell volume).

• Properties:

  • High heat capacity: Absorbs and releases heat slowly.

  • High heat of vaporization: Evaporation requires much heat (important for cooling).

  • Polar solvent: Dissolves and dissociates ionic substances; forms hydration layers.

  • Reactivity: Involved in hydrolysis and dehydration synthesis reactions.

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

Salts

• Ionic compounds that dissociate into ions in water.

• All ions are electrolytes (conduct electrical currents in solution).

• Common body salts: NaCl, KCl, calcium phosphates.

• Ionic balance is vital for homeostasis.

Acids and Bases

• Acids: Proton donors; release H+ ions in solution (e.g., HCl, acetic acid).

• Bases: Proton acceptors; release OH- ions in solution (e.g., bicarbonate, ammonia).

• pH scale: Measures concentration of H+ ions; ranges from 0 (acidic) to 14 (basic), with 7 being neutral.

• Buffers: Resist abrupt changes in pH by releasing or binding H+ ions.

2.7 Organic Compounds: Synthesis and Hydrolysis

• Organic molecules contain carbon (except CO2 and CO).

• Many are polymers (chains of monomers).

• Dehydration synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

2.8 Carbohydrates

• Include sugars and starches; contain C, H, and O in a 1:2:1 ratio.

• Three classes:

  • Monosaccharides: Single sugars (e.g., glucose, fructose).

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

  • Polysaccharides: Many sugars (e.g., starch in plants, glycogen in animals).

2.9 Lipids

• Contain C, H, O (less O than carbohydrates), sometimes P.

• Insoluble in water.

• Main types:

  • Triglycerides: Energy storage, insulation, protection.

  • Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

  • Steroids: Four interlocking rings; cholesterol is the most important steroid.

2.10 Proteins

• Comprise 10–30% of cell mass; contain C, H, O, N, sometimes S and P.

• Functions: Structural support, enzymes, transport, movement, communication, defense.

• Polymers of amino acids joined by peptide bonds.

• 20 types of amino acids; proteins are usually 100–10,000+ amino acids long.

2.11 Nucleic Acids

• Composed of C, H, O, N, P; largest molecules in the body.

• Polymers of nucleotides (nitrogen base, pentose sugar, phosphate group).

• Two major classes:

  • DNA (deoxyribonucleic acid): Genetic blueprint; double helix; located in nucleus.

  • RNA (ribonucleic acid): Links DNA to protein synthesis; single-stranded; active outside nucleus.

2.12 ATP (Adenosine Triphosphate)

• ATP is the energy currency of the cell; stores and releases chemical energy for cellular processes.

• Structure: Adenine-containing RNA nucleotide with three phosphate groups.

• ATP can be converted to ADP (adenosine diphosphate) and AMP (adenosine monophosphate) by loss of phosphate groups, releasing energy.

Additional info: This chapter provides foundational chemistry concepts essential for understanding later topics in anatomy and physiology, such as cellular structure, metabolism, and physiological regulation.