Chapter 2: The Chemistry of Microbiology – Study Notes

The Chemistry of Microbiology: Basic Fundamentals of Chemistry

Introduction

Chemistry is fundamental to understanding microbiology, as all living organisms are composed of chemical substances and depend on chemical reactions for survival. This chapter covers the basic chemical principles essential for the study of microorganisms, including atomic structure, chemical bonding, types of reactions, and the major classes of biological macromolecules.

Basic Chemical Concepts

Elements, Atoms, and Matter

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

• Atom: The smallest unit of an element, composed of protons (positive charge), neutrons (neutral), and electrons (negative charge).

• Matter: Anything that has mass and occupies space; composed of atoms.

• Atomic Number: The number of protons in an atom's nucleus; determines the element.

• Isotopes: Atoms of the same element with different numbers of neutrons; some are radioactive and decay over time.

• Atomic Mass: The sum of protons and neutrons in the nucleus.

Subatomic Particles and Electron Configuration

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus in energy levels (shells).

• Electron Shells: Electrons are arranged in shells around the nucleus; the first shell holds 2 electrons, the second holds 8, etc.

• Valence Electrons: Electrons in the outermost shell; determine chemical reactivity.

• Electronegativity: The ability of an atom to attract electrons in a chemical bond.

Example: An atom with 6 electrons (e.g., carbon) has 2 electrons in its inner shell and 4 in its valence shell.

Reading the Periodic Table

• Elements are organized by increasing atomic number.

• Groups (columns) share similar chemical properties due to similar valence electron configurations.

• Key elements in living organisms: C (carbon), H (hydrogen), O (oxygen), N (nitrogen), P (phosphorus), S (sulfur).

Ions and Chemical Bonds

• Ion: An atom or molecule that has gained or lost electrons, acquiring a charge.

• Cation: Positively charged ion (lost electrons).

• Anion: Negatively charged ion (gained electrons).

• Chemical Bond: The force holding atoms together in molecules or compounds.

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

• Covalent Bond: Formed when two atoms share one or more pairs of electrons.

• Polar Covalent Bond: Unequal sharing of electrons, resulting in partial charges (e.g., water).

• Non-Polar Covalent Bond: Equal sharing of electrons (e.g., O2).

• Hydrogen Bond: Weak attraction between a hydrogen atom (partially positive) and an electronegative atom (e.g., oxygen or nitrogen).

Chemical Reactions in Microbiology

Types of Chemical Reactions

• Synthesis Reaction (Anabolism): Two or more atoms or molecules combine to form a larger molecule. General formula: $A + B \rightarrow AB$

• Decomposition Reaction (Catabolism): A molecule is broken down into smaller components. General formula: $AB \rightarrow A + B$

• Exchange Reaction: Involves both synthesis and decomposition; atoms are exchanged between molecules. General formula: $AB + CD \rightarrow AD + CB$

• Reversible Reaction: Can proceed in either direction depending on conditions. General formula: $A + B \rightleftharpoons AB$

Energy in Chemical Reactions

• Endergonic Reaction: Requires energy input (e.g., synthesis of macromolecules).

• Exergonic Reaction: Releases energy (e.g., breakdown of glucose).

Components of Chemical Reactions

• Reactants: Starting substances in a reaction.

• Products: Substances formed as a result of the reaction.

• Enzymes: Biological catalysts that speed up reactions without being consumed.

• Indicators: Substances that show a visible change (e.g., color) to signal a reaction has occurred.

Water, Acids, Bases, and Salts

Properties of Water

• Water (H2O): Inorganic, polar molecule; excellent solvent due to polarity.

• Hydrogen Bonds: Allow water to absorb heat, making it a temperature buffer.

• Dissociation: Water can dissociate into H+ and OH- ions.

Acids, Bases, and Salts

• Acid: Substance that dissociates in water to release H+ ions.

• Base: Substance that dissociates to release OH- ions or accepts H+.

• Salt: Substance that dissociates into cations and anions, neither of which is H+ or OH-.

• Buffer: Compound that stabilizes pH by absorbing or releasing H+ as needed.

pH Scale

• pH: A measure of hydrogen ion concentration; calculated as $pH = -\log[H^+]$

• pH < 7: Acidic; pH = 7: Neutral; pH > 7: Basic (alkaline).

• Most organisms grow best between pH 6.5 and 8.5.

Organic Chemistry in Microbiology

Organic vs. Inorganic Compounds

• Organic Compounds: Always contain carbon and hydrogen (C-H bonds); e.g., carbohydrates, lipids, proteins, nucleic acids.

• Inorganic Compounds: Typically lack carbon or do not have C-H bonds; e.g., water, salts, CO2.

Macromolecules and Macronutrients

• Macromolecules: Large, complex molecules essential for life; include carbohydrates, lipids, proteins, and nucleic acids.

• Monomer: Small building block molecule (e.g., amino acid, nucleotide).

• Polymer: Large molecule made of repeating monomers (e.g., protein, DNA).

• Dehydration Synthesis: Reaction that joins monomers by removing water.

• Hydrolysis: Reaction that breaks polymers into monomers by adding water.

Functional Groups and Carbon Skeletons

• Carbon Skeleton: The chain or ring of carbon atoms forming the backbone of organic molecules.

• Functional Group: Specific group of atoms attached to the carbon skeleton that determines chemical properties (e.g., hydroxyl, carboxyl, amino, phosphate).

• R-Group: Variable side chain in amino acids and other molecules.

Major Classes of Biological Molecules

Carbohydrates

• Function: Provide energy and structural support.

• Monosaccharide: Simple sugar (e.g., glucose, fructose).

• Disaccharide: Two monosaccharides joined by a glycosidic bond (e.g., sucrose).

• Oligosaccharide: Short chain of monosaccharides (3–10 units).

• Polysaccharide: Long chain of monosaccharides (e.g., starch, cellulose, glycogen).

• Bond: Glycosidic bond (formed by dehydration synthesis).

Lipids

• Function: Energy storage, membrane structure, signaling.

• Simple Lipids (Fats/Triglycerides): Composed of glycerol and fatty acids; joined by ester bonds.

• Saturated Fat: Fatty acids with no double bonds; solid at room temperature.

• Unsaturated Fat: Fatty acids with one or more double bonds; liquid at room temperature.

• Phospholipids: Major component of cell membranes; contain a phosphate group.

• Steroids: Four fused carbon rings with functional groups (e.g., cholesterol).

• Waxes: Long-chain fatty acids bonded to long-chain alcohols; waterproofing.

• Hydrophobic: Repels water; nonpolar.

• Hydrophilic: Attracts water; polar.

Proteins

• Function: Enzymes, structural support, transport, movement, toxins.

• Amino Acid: Monomer of proteins; contains amino group, carboxyl group, hydrogen, and R-group.

• Peptide Bond: Covalent bond joining amino acids (via dehydration synthesis).

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet) via hydrogen bonds.

  • Tertiary: 3D shape due to interactions among R-groups.

  • Quaternary: Association of multiple polypeptide chains.

• Conjugated Proteins: Proteins combined with non-protein groups (e.g., glycoproteins, nucleoproteins, lipoproteins).

Enzymes

• Definition: Biological catalysts that speed up chemical reactions by lowering activation energy.

• Structure: Most are proteins with a specific active site for substrate binding.

• Function: Essential for metabolism and regulation of cellular processes.

Nucleic Acids

• Function: Store and transmit genetic information.

• Monomer: Nucleotide (composed of a pentose sugar, phosphate group, and nitrogenous base).

• DNA (Deoxyribonucleic Acid): Double-stranded helix; deoxyribose sugar; bases: adenine (A), thymine (T), cytosine (C), guanine (G).

• RNA (Ribonucleic Acid): Single-stranded; ribose sugar; bases: adenine (A), uracil (U), cytosine (C), guanine (G).

• Base Pairing in DNA: A pairs with T, G pairs with C (held by hydrogen bonds).

• Genes: Sequences of nucleotides that encode proteins.

• ATP (Adenosine Triphosphate): Nucleotide that serves as the primary energy carrier in cells.

Summary Table: Major Classes of Biological Molecules

Class	Monomer	Bond Type	Main Elements	Function
Carbohydrates	Monosaccharide	Glycosidic	C, H, O	Energy, structure
Lipids	Glycerol + Fatty Acids	Ester	C, H, O (sometimes P)	Membranes, energy storage
Proteins	Amino Acid	Peptide	C, H, O, N, (sometimes S)	Enzymes, structure, transport
Nucleic Acids	Nucleotide	Phosphodiester	C, H, O, N, P	Genetic information

Key Formulas and Equations

• pH Calculation: $pH = -\log[H^+]$

• General Synthesis Reaction: $A + B \rightarrow AB$

• General Decomposition Reaction: $AB \rightarrow A + B$

• General Exchange Reaction: $AB + CD \rightarrow AD + CB$

Conclusion

Understanding the chemical foundations of microbiology is essential for grasping how microorganisms function, grow, and interact with their environment. Mastery of these concepts provides the basis for further study in microbial metabolism, genetics, and physiology.