The Chemistry of Biology

Introduction

Understanding the chemical principles underlying biological systems is essential for the study of microbiology. This chapter introduces the basic concepts of matter, atomic structure, chemical bonds, and the major macromolecules that form the foundation of all living organisms.

Bonds, Atoms, and Molecules

Definitions and Basic Concepts

• Matter: All tangible materials that occupy space and have mass.

• Atom: The smallest unit of matter that retains the properties of an element and cannot be subdivided into smaller substances without losing its unique properties.

Subatomic Particles

• Protons (p+): Positively charged particles found in the nucleus of the atom.

• Neutrons (n0): Neutral particles also located in the nucleus.

• Electrons (e-): Negatively charged particles that orbit the nucleus in defined shells or orbitals.

Electron Orbitals and Shells

Electrons are arranged in orbitals around the nucleus. The arrangement of electrons determines the chemical properties and reactivity of an atom. The first shell holds up to 2 electrons, the second up to 8, and so on.

Major Elements in Biology

Essential Elements

Carbon, hydrogen, and oxygen are the most abundant elements in biological molecules. Other important elements include nitrogen, phosphorus, and sulfur.

Macromolecules Essential for Life

Four Major Types

• Proteins: Polymers of amino acids that perform a wide variety of functions, including catalysis (enzymes), structural support, and transport.

• Carbohydrates: Sugars and polysaccharides that serve as energy sources and structural components.

• Nucleic acids: DNA and RNA, which store and transmit genetic information.

• Lipids: Fats, oils, and phospholipids that make up cell membranes and store energy.

Types of Chemical Bonds

Overview

Chemical bonds are forces that hold atoms together in molecules. The three main types are:

• Ionic Bonds: Formed when electrons are transferred completely from one atom to another, resulting in oppositely charged ions that attract each other.

• Covalent Bonds: Formed when atoms share electrons. Covalent bonds can be single (one pair of electrons shared) or double (two pairs shared). Covalent bonds are stronger and more stable than ionic bonds.

• Hydrogen Bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom (such as oxygen or nitrogen) and another electronegative atom. Hydrogen bonds are crucial for the structure of biological molecules like DNA and proteins.

Comparison of Bond Types

Polarity and Water

Polar and Non-Polar Covalent Bonds

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

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

Water as a Polar Molecule

Water's polarity allows it to form hydrogen bonds, making it an excellent solvent and critical for biological processes.

Hydrogen Bonds in Biology

Definition and Importance

• Hydrogen bond: An attractive intermolecular force between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom. Although stronger than most other intermolecular forces, hydrogen bonds are much weaker than ionic or covalent bonds.

• Biological significance: Hydrogen bonds stabilize the structures of proteins and nucleic acids and are essential for the properties of water.

Macromolecule Synthesis and Breakdown

Dehydration Synthesis and Hydrolysis

• Dehydration synthesis: The process by which monomers are joined to form polymers, releasing a molecule of water for each bond formed.

• Hydrolysis: The process by which polymers are broken down into monomers by the addition of water.

Acidity, Alkalinity, and the pH Scale

Definitions

• Acidic solution: Releases excess hydrogen ions (H+).

• Alkaline (basic) solution: Releases excess hydroxyl ions (OH-).

The pH Scale

• Measures the concentration of hydrogen ions in a solution.

• Ranges from 0 (most acidic) to 14 (most basic).

• Each increment represents a tenfold change in ion concentration (logarithmic scale).

• Formula:

Hydrogen Ion and Hydroxide Ion Concentrations at Different pH Values

Additional info: The pH scale is fundamental in microbiology for understanding enzyme activity, microbial growth, and environmental adaptation.