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

Introduction to the Chemistry of Life

This chapter provides an essential overview of basic chemistry concepts as they relate to anatomy and physiology. Understanding atoms, chemical bonds, water, pH, and biological molecules is fundamental for comprehending physiological processes in the human body.

Basic Chemistry

Atoms and Subatomic Particles

Atoms are the smallest units of an element that retain all the properties of that element. They are composed of three main subatomic particles:

• Protons (+ charge): Determine the element's identity and are found in the nucleus.

• Neutrons (no charge): Also located in the nucleus; contribute to atomic mass and can vary in number, resulting in isotopes.

• Electrons (- charge): Orbit the nucleus and are involved in chemical bonding and reactions.

Atomic number is the number of protons in an atom and defines the element. Atomic mass is the sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons. Some isotopes are unstable (radioactive) and emit radiation, which can be used in medical imaging and treatments.

Ions and Their Charges

An ion is an atom or molecule with a net electric charge due to the loss or gain of electrons.

• Neutrally charged atom: Number of electrons equals number of protons.

• Anion: Negatively charged ion (more electrons than protons).

• Cation: Positively charged ion (fewer electrons than protons).

The charge of an atom determines how it bonds with other atoms.

Chemical Bonds

Ionic Bonds

Ionic bonds are formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other.

• Example: Sodium (Na+) and Chloride (Cl-) combine to form table salt (NaCl).

Covalent Bonds

Covalent bonds are formed when atoms share pairs of electrons.

• Non-polar covalent bonds: Electrons are shared equally (e.g., O2 molecule).

• Polar covalent bonds: Electrons are shared unequally, resulting in partial charges (e.g., H2O molecule).

Hydrogen Bonds

Hydrogen bonds are weak attractions between the slightly positive hydrogen atom of one molecule and the slightly negative atom (often oxygen or nitrogen) of another molecule. These are crucial for the properties of water and the structure of biological molecules like DNA.

Elements in the Human Body

Major, Mineral, and Trace Elements

The human body is composed of several elements, classified by their abundance:

Type	Examples	Role in Body
Major Elements (96%)	O, C, H, N	Form the bulk of body mass (water, proteins, carbohydrates, fats)
Mineral Elements (<4%)	Na, K, Ca, Mg, P, S, Cl	Essential for nerve function, muscle contraction, bone structure
Trace Elements	Fe, Zn, Cu, I, Se, etc.	Required in small amounts for enzyme function and other processes

Additional info: The periodic table highlights which elements are most relevant to human physiology.

Properties of Water and pH

Water

Water is vital for life due to its unique properties:

• High heat capacity: Absorbs and retains heat, helping regulate body temperature.

• Excellent solvent: Dissolves many substances, facilitating chemical reactions.

• Hydrophilic vs. Hydrophobic: Polar molecules (hydrophilic) dissolve in water; non-polar molecules (hydrophobic) do not.

pH and Buffers

pH measures the concentration of hydrogen ions (H+) in a solution:

• pH < 7: Acidic (higher H+ concentration)

• pH = 7: Neutral

• pH > 7: Basic (lower H+ concentration)

Buffers are substances that minimize changes in pH, helping maintain homeostasis. For example, bicarbonate (HCO3-) neutralizes stomach acid as food enters the intestine.

Electrolytes

Electrolytes are substances that conduct electricity when dissolved in water. They are essential for nerve impulses, muscle contraction, and maintaining fluid balance.

• Common electrolytes: Na+, K+, Ca2+, HCO3-

Biological Macromolecules

Carbohydrates

Carbohydrates are sugars and starches that provide energy and structural support.

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

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

• Polysaccharides: Long chains (e.g., starch, fiber)

• Functions: Energy source, cell surface markers, structural components

Lipids

Lipids include fats, oils, and related molecules. They are insoluble in water and serve several functions:

• Types: Fatty acids, steroids, phospholipids

• Functions: Energy storage, cell membrane structure, hormones, digestion

Proteins

Proteins are made of amino acids and are the main structural and functional molecules in the body.

• Structure: Sequence of amino acids determines protein shape and function

• Functions: Structural support, enzymes, transport, signaling, immune defense

Enzymes are proteins that catalyze (speed up) chemical reactions by lowering activation energy. Examples include lactase, amylase, and DNA polymerase.

Nucleic Acids

Nucleic acids are polymers of nucleotides and are essential for genetic information and energy transfer.

• DNA: Stores genetic information

• RNA: Involved in protein synthesis

• ATP: Main energy currency of the cell

Key Equations and Concepts

• Atomic mass: $\text{Atomic mass} = \text{Number of protons} + \text{Number of neutrons}$

• pH calculation: $\text{pH} = -\log_{10}[\text{H}^+]$

Additional info: Understanding these chemical principles is foundational for studying physiological processes such as nerve conduction, muscle contraction, metabolism, and genetic inheritance.