Chapter 2: Basic Chemistry – Essentials of Human Anatomy & Physiology

Basic Chemistry

Introduction

Chemistry forms the foundation for understanding the structure and function of the human body. This chapter introduces the essential chemical principles needed for the study of anatomy and physiology, focusing on matter, energy, atomic structure, chemical bonds, and the major classes of biological molecules.

Matter and Energy

Definitions and Differences

• Matter: Anything that occupies space and has mass. All substances in the body are forms of matter.

• Energy: The capacity to do work or cause change. Energy does not have mass or occupy space.

Major Forms of Energy in the Body

• Chemical Energy: Stored in the bonds of chemical substances; released during chemical reactions (e.g., ATP hydrolysis).

• Electrical Energy: Results from movement of charged particles (e.g., nerve impulses).

• Mechanical Energy: Directly involved in moving matter (e.g., muscle contraction).

Elements and Atoms

Elements

• Element: A pure substance that cannot be broken down into simpler substances by ordinary chemical means.

• The four elements that form the bulk of body matter are: Oxygen (O), Carbon (C), Hydrogen (H), and Nitrogen (N).

Atoms

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

• Subatomic particles:

  • Protons: Positive charge (+), located in the nucleus.

  • Neutrons: No charge (neutral), located in the nucleus.

  • Electrons: Negative charge (−), orbit the nucleus in electron shells.

Chemical Bonds and Reactions

Chemical Bonds

• Chemical reactions involve the interaction of electrons to make and break chemical bonds.

• Ionic Bonds: Formed when electrons are transferred from one atom to another, creating ions (e.g., NaCl).

• Covalent Bonds: Formed when atoms share electrons.

  • Polar Covalent Bonds: Unequal sharing of electrons (e.g., water).

  • Nonpolar Covalent Bonds: Equal sharing of electrons (e.g., O2).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (important in water and DNA structure).

Chemical Reactions

• Synthesis Reactions: Two or more atoms/molecules combine to form a larger molecule. $A + B \rightarrow AB$

• Decomposition Reactions: A molecule is broken down into smaller molecules or atoms. $AB \rightarrow A + B$

Molecules, Compounds, and Mixtures

Definitions

• Molecule: Two or more atoms chemically bonded together (e.g., O2).

• Compound: A molecule that contains atoms of two or more different elements (e.g., H2O).

Inorganic and Organic Compounds

Distinguishing Features

• Inorganic Compounds: Usually lack carbon; include water, salts, acids, and bases.

• Organic Compounds: Contain carbon; include carbohydrates, lipids, proteins, and nucleic acids.

Importance of Water

• Water is vital for body homeostasis due to its high heat capacity, polarity/solvent properties, chemical reactivity, and cushioning.

• Examples: Dissolves nutrients, regulates temperature, participates in chemical reactions.

Salts, Acids, and Bases

• Salt: Ionic compound that dissociates into ions in water.

• Acid: Releases hydrogen ions (H+) in solution.

• Base: Releases hydroxide ions (OH−) or accepts H+ in solution.

pH Concept

• pH measures the concentration of hydrogen ions in a solution.

• Blood pH is tightly regulated around 7.35–7.45.

Organic Molecules: Carbohydrates, Lipids, Proteins, Nucleic Acids

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis: Joins monomers by removing water molecules.

• Hydrolysis: Breaks polymers into monomers by adding water molecules.

Carbohydrates vs. Lipids

Feature	Carbohydrates	Lipids
Building Blocks	Monosaccharides (simple sugars)	Fatty acids & glycerol
Structure	Ring-shaped	Long hydrocarbon chains
Function	Primary energy source	Energy storage, insulation, cell membranes

DNA and RNA

• DNA (Deoxyribonucleic Acid): Double-stranded, stores genetic information.

• RNA (Ribonucleic Acid): Single-stranded, involved in protein synthesis.

ATP (Adenosine Triphosphate)

• ATP is the primary energy carrier in cells.

• Energy is released when ATP is hydrolyzed to ADP and inorganic phosphate. $ATP + H_2O \rightarrow ADP + P_i + energy$