Chemistry of Life: Foundations for Microbiology

Chemistry of Life

Introduction

The chemistry of life forms the basis for understanding microbiology, as all living organisms are composed of atoms and molecules that interact through chemical reactions. This section covers fundamental concepts such as matter, atomic structure, chemical bonds, reactions, and the properties of water and organic molecules, all of which are essential for microbial life.

Basic Chemical Concepts

Matter, Elements, Atoms, and Ions

• Matter: Anything that occupies space and has mass.

• Atom: The smallest unit of an element, indivisible by natural forces.

• Element: A type of atom distinguished by its atomic number (number of protons).

• Ion: An atom or molecule that has gained or lost electrons, resulting in a positive (cation) or negative (anion) charge.

• Example: Sodium ion (Na+) and chloride ion (Cl-) in table salt.

Atomic Structure and Related Terms

• Atomic Nucleus: The central part of an atom containing protons (positive charge) and neutrons (no charge).

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

• Valence: The number of electrons in the outermost shell available for chemical bonding.

• Isotope: Atoms of the same element with different numbers of neutrons; some are radioactive.

• Electron: Negatively charged particles orbiting the nucleus in shells.

Chemical Bonds

Types and Strengths of Chemical Bonds

• Covalent Bonds: Electrons are shared between atoms.

  • Nonpolar: Equal sharing (e.g., carbon backbones).

  • Polar: Unequal sharing (e.g., water).

• Ionic Bonds: Electrons are transferred from one atom to another, forming ions.

  • Example: NaCl (table salt).

• Hydrogen Bonds: Weak bonds involving hydrogen with a slight positive charge attracting oxygen or nitrogen with a slight negative charge. Important for molecular shape.

• Van der Waals Forces: Weak interactions based on proximity; important for selectivity and specificity.

Bond Type	Strength	Example
Covalent	Strongest	Water (H2O)
Ionic	Strong	NaCl
Hydrogen	Weak	DNA base pairing
Van der Waals	Weakest	Protein folding

Chemical Reactions

Types of Chemical Reactions

• Dehydration Synthesis: Water is removed to combine two compounds; endergonic (requires energy).

• Hydrolysis: Water is added to split a compound; exergonic (releases energy).

• Redox (Reduction-Oxidation) Reactions: Involve changes in oxidation number; oxidation is loss of electrons, reduction is gain of electrons. These reactions are coupled.

• Exchange Reactions: Molecules are transferred and recombined; breaking bonds releases energy.

Chemical Notation

Rules of Chemical Notation

• Reactants are substances entering a reaction; products are formed.

• Arrows indicate reaction direction; bidirectional arrows indicate reversibility.

• Subscripts show number of atoms; coefficients show number of molecules.

• Superscripts (+/-) indicate ions.

• Atoms are rearranged, not created or destroyed.

Acid-Base Balance and pH Scale

Acids, Bases, and pH

• Acids: Release hydrogen ions (H+) in water.

• Bases: Release hydroxyl ions (OH-).

• pH Scale: Measures acidity/alkalinity from 0 (acidic) to 14 (basic); 7 is neutral.

• Each pH unit represents a tenfold change in H+ concentration.

Properties of Water

Physical and Chemical Properties

• Exists as liquid, solid, and gas.

• High heat capacity and cohesive properties.

• Surface tension and capillary action due to cohesion and adhesion.

• Universal solvent for many biological reactions.

Solutions and Concentrations

• Solvent: Liquid in which substances dissolve (e.g., water).

• Solute: Substance dissolved in solvent.

• Solution: Combination of solvent and solute.

• Hypertonic: Higher solute concentration outside cell; cell loses water.

• Hypotonic: Higher solute concentration inside cell; cell gains water.

• Isotonic: Equal solute concentration; no net water movement.

• Hydrophilic: Water-loving, soluble compounds.

• Hydrophobic: Water-repelling, insoluble compounds.

Organic Molecules

Common Properties

• Contain carbon and hydrogen atoms.

• Form backbones or rings.

• Major types: proteins, carbohydrates, lipids, nucleic acids.

• Each type is composed of specific monomers.

Carbohydrates

Structure and Function

• Monomers: Monosaccharides (e.g., glucose).

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

• Polysaccharides: Many monosaccharides (e.g., cellulose).

• Ratio: C:H:O is 2:1:2.

• Functions: Energy source, structural components.

Proteins and Amino Acids

Structure and Function

• Monomers: Amino acids (20 types).

• Each amino acid has an amine group, carboxyl group, and variable R group.

• Sequence determines protein shape and function.

Protein Structure Levels

• Primary: Sequence of amino acids.

• Secondary: Folding into β-sheets or α-helices.

• Tertiary: Globular shape, bonds, hydrophobic/hydrophilic interactions.

• Quaternary: Multiple polypeptides forming a functional unit.

Lipids

Types and Functions

• Triglycerides: Glycerol + 3 fatty acids; energy storage.

• Phospholipids: Glycerol, 2 fatty acids, phosphate; cell membranes.

• Cholesterol: Sterol + alcohol; precursor for vitamins and hormones.

• Prostaglandins: Chemical messengers.

Steroids

• Carbon skeleton of 4 fused rings.

• Functional groups determine type (anabolic, sex, mineralocorticoids, glucocorticoids).

Nucleic Acids and Nucleotides

Structure and Function

• Monomers: Nucleotides (pentose sugar, phosphate, nitrogen base).

• Sugar-phosphate backbone; bases are purines (adenine, guanine) or pyrimidines (cytosine, thymine, uracil).

• Functions: Genetic information storage, protein synthesis, energy transfer.

DNA and RNA

• DNA: Double helix, deoxyribose sugar, bases A-T, G-C; stores genetic information.

• RNA: Single strand, ribose sugar, bases A-U, G-C; involved in protein synthesis (mRNA, rRNA, tRNA).

Adenosine Triphosphate (ATP)

Structure and Function

• ATP is the energy molecule of cells.

• Energy released during catabolism is stored in ATP's high-energy phosphate bonds.

• ATP can lose phosphate groups to become ADP or AMP, releasing energy for cellular processes.

• ATP is regenerated through photosynthesis or anabolism.

Summary Table: Major Biomolecules

Type	Monomer	Structure	Function
Carbohydrates	Monosaccharide	C:H:O ratio 2:1:2	Energy, structure
Proteins	Amino acid	Amine, carboxyl, R group	Enzymes, structure, signaling
Lipids	Fatty acid, glycerol	Hydrophobic tails, hydrophilic heads	Energy, membranes, hormones
Nucleic Acids	Nucleotide	Sugar, phosphate, base	Genetic info, protein synthesis

Key Equations

Sample Chemical Equation

Photosynthesis:

$6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O} \rightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2$

ATP Hydrolysis

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

Conclusion

Understanding the chemistry of life is fundamental for microbiology, as it explains how microbial cells are built, how they function, and how they interact with their environment. Mastery of these concepts is essential for further study in microbial metabolism, genetics, and cell structure.