Biology 1 - Lesson 2: Basic Chemistry of Life

Life at its core is governed by chemical principles. To understand biological processes—whether metabolic reactions, genetic instructions, or cellular organization—it is essential to grasp how atoms bond and interact to form molecules that sustain life. This lesson explores atomic structure, chemical bonding, the role of water, acidity/alkalinity (pH), and the significance of carbon-based compounds. Each concept underpins diverse physiological processes, from energy transformations to information flow in cells.

Atoms and Elements

Atoms are the fundamental units of matter. Every atom is composed of three primary subatomic particles:

• Protons: positively charged, located in the nucleus.
• Neutrons: neutral particles, also in the nucleus.
• Electrons: negatively charged, orbiting the nucleus in orbitals or shells.

Subatomic Particles and Their Properties

Particle	Charge	Relative Mass	Location
Proton (p+)	+1	1 (approx.)	Nucleus
Neutron (n)	0	1 (approx.)	Nucleus
Electron (e-)	-1	~1/1840	Orbitals (shells)

An element’s chemical identity depends on its proton count (atomic number). The arrangement of electrons influences an element’s reactivity. Biologically relevant elements—like hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur— dominate the composition of living organisms, forming the frameworks of crucial biomolecules.

Key Biological Elements

While dozens of elements can appear in living organisms, only a handful make up the majority of biomass. The figure below shows an approximate distribution of major elements in the human body (though proportions vary slightly across species).

A donut chart showing approximate elemental composition in humans, along with a legend displaying element names and percentages. Oxygen, carbon, hydrogen, and nitrogen make up the bulk of biomass.

Isotopes and Their Uses

Atoms of the same element that vary in neutron number are known as isotopes. Although most isotopes remain stable, some are radioactive (radioisotopes), decaying at predictable rates and emitting particles/energy. Such radioisotopes serve important roles in:

• Research: tracing metabolic pathways or enzymatic processes (e.g., ¹⁴C in photosynthesis studies).
• Medical Imaging: PET scans using isotopes (like ¹⁸F) for tumor detection.
• Fossil Dating: radiocarbon (¹⁴C) to estimate ages of organic remains.

Chemical Bonds

Living systems rely on stable molecule formation through chemical bonds:

• Covalent Bonds: Atoms share electrons (single, double, or triple). These bonds are strong, forming frameworks of biomolecules like sugars, proteins, and nucleic acids.
• Ionic Bonds: One atom transfers electrons to another, creating charged ions. In aqueous environments, ions can separate (e.g., Na⁺ and Cl^-), essential for electrical signals in nerve cells.
• Hydrogen Bonds: Partial positive charges on hydrogen are drawn to partial negative atoms (often O, N). Weaker than covalent or ionic bonds, but collectively crucial for stabilizing DNA structure, protein folding, etc.

Other intermolecular forces like van der Waals and hydrophobic interactions further shape molecular conformations.

Water and Its Properties

Water’s chemical properties are indispensable for life:

• Cohesion & Adhesion: Hydrogen bonding allows water to cling to itself (cohesion) and to surfaces (adhesion), enabling capillary action in plants and surface tension.
• High Specific Heat: Water resists rapid temperature changes, helping organisms maintain stable internal conditions.
• Ice Density Anomaly: Ice is less dense than liquid water, floating and insulating aquatic systems in cold environments.
• Solvent Capacity: Water’s polarity dissolves ionic/polar substances, essential for transport and reactions within cells.

pH and Buffers

Maintaining pH homeostasis is vital:

• pH Scale: Ranges 0–14; 7 is neutral, below is acidic, above is basic.
• Buffers: Compounds that stabilize pH by binding or releasing H⁺/OH^-. For instance, the bicarbonate buffer in blood keeps pH near 7.4.

Even minor pH deviations can disrupt metabolic reactions or enzyme function.

Carbon-Based Compounds

Carbon forms up to four covalent bonds, allowing complex, diverse structures crucial to life:

• Hydrocarbons: Carbon-hydrogen frameworks, energy-rich, can be linear, branched, or ring-shaped.
• Functional Groups: Groups like hydroxyl (–OH) or amino (–NH₂) attach to carbon backbones, modulating reactivity and water solubility.
• Biomolecules: Proteins, lipids, carbohydrates, nucleic acids all rely on carbon skeletons, combined with H, O, N, P, S.

Significance for Biological Systems

An understanding of basic chemistry—atomic structure, bond types, water’s properties, pH regulation, and carbon’s bonding versatility—provides the framework for studying how molecules assemble into cells and how metabolic pathways function. These concepts set the stage for exploring macromolecules, metabolism, and regulatory mechanisms that collectively sustain life’s complexity across all biological scales.