Chemical Principles in Microbiology: Structure, Bonds, and Biological Molecules

Chapter 2: Chemical Principles

Introduction

Chemical principles are foundational for understanding microbiology, as microorganisms rely on chemical building blocks for growth and metabolic functions. The breakdown and synthesis of these molecules are governed by chemical reactions, which are essential for cellular processes.

• Microorganisms use atoms to make chemical building blocks for growth and other functions.

• Breaking chemical bonds releases energy and forms new substances.

The Structure of Atoms

Atoms are the smallest units of matter that retain chemical properties. They consist of subatomic particles and form the basis of all chemical reactions in living organisms.

• Atoms: Smallest component of a substance; cannot be subdivided without losing properties.

• Subatomic particles:

  • Protons: Positively charged, found in nucleus.

  • Neutrons: Neutral, found in nucleus.

  • Electrons: Negatively charged, move around nucleus in shells.

Example: The hydrogen atom consists of one proton and one electron.

Chemical Elements

Chemical elements are pure substances composed of only one type of atom. Each element has a unique atomic number and chemical properties.

• 92 naturally occurring elements; 26 are found in living things.

• Major elements in biology: Hydrogen, Carbon, Nitrogen, Oxygen.

Electronic Configuration

Electrons are arranged in shells corresponding to different energy levels. The arrangement determines how atoms interact and bond.

• Atoms are most stable when their outer shell is full.

• Atoms with incomplete outer shells tend to react with other atoms.

Chemical Bonds

Chemical bonds form when atoms share, gain, or lose electrons to achieve stability. These bonds are essential for forming molecules and compounds.

• Ionic Bonds: Formed when atoms gain or lose electrons, resulting in attraction between oppositely charged ions.

• Covalent Bonds: Formed when atoms share electrons; most common in biological molecules.

• Hydrogen Bonds: Weak bonds; occur when a hydrogen atom covalently bonded to one atom is attracted to another atom.

Example: Water molecules are held together by covalent bonds, and hydrogen bonds form between water molecules.

Chemical Reactions

Chemical reactions involve the making or breaking of bonds between atoms. They are essential for metabolism and energy transfer in cells.

• Synthesis Reactions: Atoms, ions, or molecules combine to form new, larger molecules.

  • General form: $A + B \rightarrow AB$

  • Example: Formation of starch from glucose units.

• Decomposition Reactions: Bonds are broken to produce smaller parts from a larger molecule.

  • General form: $AB \rightarrow A + B$

  • Example: Breakdown of sucrose into glucose and fructose during digestion.

• Reversible Reactions: Can proceed in both directions under suitable conditions.

  • General form: $A + B \rightleftharpoons AB$

Inorganic Compounds

Inorganic compounds are small molecules that do not contain both carbon and hydrogen. They play important roles in biological systems.

• Examples: Water, Oxygen, Carbon Dioxide, Salts, Acids, Bases.

• Water: Essential for life; acts as a solvent, participates in chemical reactions, and regulates temperature.

• Acids: Substances that dissociate into one or more hydrogen ions and one or more negative ions.

• Bases: Substances that dissociate into one or more negatively charged hydroxide ions and one or more positive ions.

• Salts: Dissociate in water into cations and anions.

Acid-Base Balance

Maintaining acid-base balance is crucial for organism survival, as enzymes and biochemical reactions are sensitive to pH changes.

• pH: Measures the acidity or alkalinity of a solution.

  • Logarithmic scale: Each unit change represents a tenfold change in hydrogen ion concentration.

  • Microbial growth occurs at specific pH ranges (e.g., bacteria: 6.5–7.5).

Organic Compounds

Organic compounds always contain carbon and hydrogen, and are structurally complex. They are held together mainly by covalent bonds and perform complex biological functions.

• Macromolecules: Large organic molecules formed by joining smaller molecules (monomers) via synthesis reactions.

• Types: Carbohydrates, Lipids, Proteins, Nucleic Acids.

Carbohydrates

Carbohydrates are composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

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

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

• Polysaccharides: Chains of many monosaccharides (e.g., starch, glycogen, cellulose).

Lipids

Lipids are non-water-soluble organic molecules that form cell membranes and store energy.

• Simple Lipids: Triglycerides (glycerol + fatty acids).

• Complex Lipids: Contain additional elements (e.g., phospholipids).

• Steroids: Include cholesterol and hormones; found in plasma membranes.

Proteins

Proteins are large molecules containing carbon, hydrogen, oxygen, and nitrogen. They perform structural, enzymatic, and transport functions.

• Composed of amino acids linked by peptide bonds.

• Functions: Enzymes, transport, structural support, movement.

Nucleic Acids

Nucleic acids carry genetic information and are composed of nucleotides (sugar, phosphate group, nitrogenous base).

• DNA: Double-stranded, contains genetic material; bases are adenine, thymine, guanine, cytosine.

• RNA: Single-stranded, involved in protein synthesis; bases are adenine, uracil, guanine, cytosine.

Adenosine Triphosphate (ATP)

ATP is the energy-carrying molecule of all cells. It stores and releases energy for cellular processes.

• ATP consists of adenosine and three phosphate groups.

• Energy is released when ATP is hydrolyzed to ADP and inorganic phosphate.

• Equation: $\text{ATP} \rightarrow \text{ADP} + \text{P}_i$

Bond Type	Formation	Strength	Biological Example
Ionic	Transfer of electrons	Moderate	NaCl (table salt)
Covalent	Sharing of electrons	Strong	Water (H2O)
Hydrogen	Attraction between H and electronegative atom	Weak	Between water molecules

Additional info: The notes have been expanded to include definitions, examples, and context for each major concept, as well as a summary table comparing bond types.