The Chemistry of Life: Foundations for Anatomy & Physiology

The Chemistry of Life

Introduction

Chemistry is fundamental to understanding biological processes in Anatomy & Physiology. The structure and function of atoms, molecules, and chemical bonds underpin the behavior of cells and tissues.

Atoms and Elements

Structure of the Atom

• Nucleus: The central part of an atom containing protons and neutrons.

• Protons: Positively charged particles in the nucleus. The number of protons defines the atomic number and the element.

• Neutrons: Neutral particles in the nucleus. They contribute to atomic mass but do not affect charge.

• Electrons: Negatively charged particles orbiting the nucleus in electron shells.

• Electrically Neutral: An atom is neutral when the number of protons equals the number of electrons.

Elements and the Periodic Table

• Element: A pure substance consisting of only one type of atom, defined by its atomic number.

• Periodic Table: Organizes elements by increasing atomic number and similar chemical properties.

• Major Elements in the Human Body: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N).

• Mineral Elements: Seven essential minerals (e.g., Na, K, Ca, Mg, P, S, Cl).

• Trace Elements: Thirteen elements required in minute amounts (e.g., Fe, Zn, Cu).

Periodic Table Organization

• Electron Shells: Energy levels where electrons reside.

  • 1st Shell: Holds up to 2 electrons.

  • 2nd Shell: Holds up to 8 electrons.

  • 3rd Shell: Holds up to 18 electrons.

  • Valence Shell: Outermost shell; determines chemical reactivity.

  • Valence Electrons: Electrons in the valence shell involved in bonding.

Chemical Bonds and Stability

Stability of Atoms

• Duet Rule: Atoms (like hydrogen) are stable with 2 electrons in their valence shell.

• Octet Rule: Most atoms are stable with 8 electrons in their valence shell.

• Unstable Atoms: Atoms with incomplete valence shells are reactive and participate in chemical processes.

Chemical Bonds

• Molecule: Two or more atoms chemically bonded (e.g., O2, H2).

• Compound: Molecule containing two or more different elements (e.g., H2O).

• Chemical Bond: An energy relationship or attractive force between atoms, not a physical structure.

Classification Table: Molecule vs. Compound

Substance	Molecule	Compound
O2	Yes	No
H2O	Yes	Yes
He	No	No
H2	Yes	No
N2	Yes	No

Ionic Bonds

• Ionic Bond: Formed by the transfer of electrons from one atom to another, resulting in charged ions.

• Cation: Positively charged ion (e.g., Na+).

• Anion: Negatively charged ion (e.g., Cl-).

• Electrolytes: Ionic compounds that dissociate in water to conduct electricity (e.g., NaCl).

Covalent Bonds

• Covalent Bond: Formed by the sharing of electrons between atoms.

• Nonpolar Covalent Bond: Electrons are shared equally (e.g., H2, O2, N2).

• Polar Covalent Bond: Electrons are shared unequally, creating partial charges (e.g., H2O).

Relative Bond Strength

• Covalent bonds are generally stronger than ionic bonds and hydrogen bonds.

• Hydrogen bonds are weak attractions between polar molecules, important in water and biological macromolecules.

Properties of Water

Surface Tension

• Surface Tension: The cohesive force at the surface of water due to hydrogen bonding.

Solubility

• Solution: Homogeneous mixture of solvent and solute.

• Solvent: Substance that dissolves the solute (water is the universal solvent).

• Solute: Substance dissolved in the solvent.

• Hydrophobic Solutes: Do not dissolve in water (e.g., oils).

• Hydrophilic Solutes: Dissolve easily in water (e.g., salts, sugars).

High Heat Capacity

• High Heat Capacity: Water absorbs and retains heat, helping to stabilize body temperature.

Thermoregulation

• Thermoregulation: Water's properties help regulate temperature in living organisms.

Protection & Lubrication

• Protection & Lubrication: Water cushions organs and lubricates joints.

Organic vs. Inorganic Molecules

Comparison Table

Organic Molecules	Inorganic Molecules
Contain carbon and hydrogen	Do not always contain carbon
Examples: Carbohydrates, lipids, proteins, nucleic acids	Examples: Water, salts, acids, bases
Complex structures	Simpler structures
Found in living organisms	Found in both living and non-living systems

Adenosine Triphosphate (ATP)

Role and Energy Release

• ATP: The primary energy carrier in cells.

• Energy Release: ATP releases energy when its terminal phosphate bond is broken, forming ADP and inorganic phosphate.

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

• Role in Cells: ATP powers cellular processes such as muscle contraction, active transport, and biosynthesis.

Periodic Table: Metals vs. Nonmetals

Classification Table

Metals	Nonmetals
Left of the red "staircase" on the periodic table	Right of the red "staircase"
Good conductors of heat and electricity	Poor conductors
Examples: Na, Mg, Ca	Examples: C, N, O, F, Cl

Additional info: The periodic table is a key tool for identifying element properties, electron configurations, and predicting chemical behavior in biological systems.