Chapter 2: Chemistry Comes Alive

Introduction

Chemistry forms the foundation of all physiological processes in the human body. Understanding basic chemistry and biochemistry is essential for interpreting how the body functions, from cellular metabolism to organ system regulation. This chapter covers the essential chemical principles relevant to Anatomy & Physiology.

2.1 Matter and Energy

Matter

Matter is anything that has mass and occupies space. It can be observed, smelled, or felt. The three states of matter are:

• 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. It exists in two main forms:

• Kinetic energy: Energy in action.

• Potential energy: Stored energy.

Energy can be transformed from one form to another, but some energy is lost as heat during conversion.

• Chemical energy: Stored in chemical bonds.

• Electrical energy: Movement of charged particles.

• Mechanical energy: Directly involved in moving matter.

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

2.2 Atoms and Elements

Elements

Elements are pure substances that cannot be broken down by ordinary chemical methods. Four elements—carbon, oxygen, hydrogen, and nitrogen—make up 96% of the human body.

Atoms

Atoms are the smallest units of elements, consisting of:

• 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

Atoms combine to form molecules and compounds:

• Molecule: Two or more atoms bonded together.

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

Mixtures

Mixtures are combinations of two or more components physically intermixed. The three basic types are:

• Solutions: Solute particles are very tiny and do not settle out or scatter light.

• Colloids: Solute particles are larger and scatter light but do not settle out.

• Suspensions: 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 seek stability by achieving a full valence shell, often 8 electrons (the octet rule).

Chemically Inert and Reactive Elements

Elements with complete valence shells are chemically inert, while those with incomplete shells are reactive.

Types of Chemical Bonds

• Ionic bonds: Transfer of electrons between atoms, forming charged ions (cations and anions).

• Covalent bonds: Sharing of electrons between atoms. Can be single, double, or triple bonds.

• Hydrogen bonds: Weak attractions between electropositive hydrogen and electronegative atoms.

Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, resulting in oppositely charged ions.

Covalent Bonds

Covalent bonds involve the sharing of electrons. The number of shared pairs determines if the bond is single, double, or triple.

Polar and Nonpolar Covalent Bonds

• Nonpolar: Equal sharing of electrons, resulting in balanced molecules (e.g., CO2).

• Polar: Unequal sharing, resulting in molecules with charged poles (e.g., H2O).

Hydrogen Bonds

Hydrogen bonds are weak attractions that help stabilize large molecules, such as proteins and DNA.

Types of Chemical Reactions

Synthesis (Combination) Reactions

Atoms or molecules combine to form larger, more complex molecules. These reactions are anabolic (building).

Decomposition Reactions

Breakdown of a molecule into smaller molecules or atoms. These reactions are catabolic (bond-breaking).

Energy Flow in Chemical Reactions

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

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

Rate of Chemical Reactions

The speed of reactions is influenced by temperature, concentration, particle size, and catalysts (including enzymes).

Part 2—Biochemistry

Inorganic Compounds

Inorganic compounds include water, salts, acids, and bases. They do not contain carbon (with exceptions).

Water

Water is the most abundant inorganic compound in the body, accounting for 60–80% of cell volume. Its properties include:

• High heat capacity: Absorbs and releases heat with little temperature change.

• High heat of vaporization: Evaporation requires much heat, aiding cooling.

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

• Reactivity: Participates in hydrolysis and dehydration synthesis.

• Cushioning: Protects organs from trauma.

Salts

Salts are ionic compounds that dissociate in water to form electrolytes, which conduct electrical currents. Examples include sodium chloride (NaCl), potassium chloride (KCl), and calcium phosphates.

Acids and Bases

Acids are proton donors, releasing hydrogen ions (H+). Bases are proton acceptors, releasing hydroxyl ions (OH-). The pH scale measures hydrogen ion concentration:

• Acidic: pH 0–6.99

• Neutral: pH 7

• Alkaline (basic): pH 7.01–14

Buffers

Buffers resist changes in pH by releasing or binding hydrogen ions. The bicarbonate buffer system is crucial for blood pH regulation.

2.7 Organic Compounds: Synthesis and Hydrolysis

Organic molecules contain carbon and include carbohydrates, lipids, proteins, and nucleic acids. Many are polymers made of monomers, synthesized by dehydration synthesis and broken down by hydrolysis.

2.8 Carbohydrates

Carbohydrates are sugars and starches composed of carbon, hydrogen, and oxygen. They are classified as:

• Monosaccharides: Single sugar units (e.g., glucose).

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

• Polysaccharides: Many sugars linked together (e.g., starch, glycogen).

2.9 Lipids

Lipids are hydrophobic molecules including triglycerides, phospholipids, and steroids. They function in energy storage, insulation, and cell membrane structure.

Phospholipids

Phospholipids have a polar, hydrophilic head and nonpolar, hydrophobic tails, forming the basis of cell membranes.

2.10 Proteins

Proteins are polymers of amino acids and perform diverse functions, including structural support, catalysis, transport, movement, communication, and defense.

• Structural proteins: Provide mechanical support (e.g., collagen).

• Enzyme proteins: Catalyze biochemical reactions.

• Transport proteins: Move substances in blood or across membranes.

• Contractile proteins: Cause movement (e.g., actin and myosin).

• Communication proteins: Transmit signals (e.g., hormones).

• Defensive proteins: Protect against disease (e.g., antibodies).

2.11 Nucleic Acids

Nucleic acids (DNA and RNA) are polymers of nucleotides, containing a nitrogen base, pentose sugar, and phosphate group. DNA stores genetic information; RNA is involved in protein synthesis.

2.12 ATP (Adenosine Triphosphate)

ATP is the primary energy carrier in cells. It consists of an adenine-containing RNA nucleotide with three phosphate groups. Energy is released when ATP is hydrolyzed to ADP or AMP.

Key Equations

• ATP Hydrolysis:

• pH Calculation:

Additional info: These notes expand on the original lecture slides by providing definitions, examples, and academic context for each topic, ensuring completeness and clarity for exam preparation.