Microbiology: Chemical Principles – Structured Study Notes

Chapter 2: Chemical Principles

Learning Goals

• Explain atomic structure and chemical elements

• Compare types of chemical bonds and formulas

• Describe water chemistry, pH, and buffers

• Distinguish inorganic vs. organic compounds

• Explain how macromolecules work and affect microbes

Section 1: Atoms & Atomic Structure

Introduction

Atoms are the fundamental units of matter, consisting of subatomic particles that determine their chemical properties and behavior.

• Atoms: Smallest unit of an element

• Subatomic particles:

  • Protons (+)

  • Neutrons (0)

  • Electrons (-)

• Atomic number: Number of protons

• Atomic mass: Sum of protons and neutrons

• Isotopes: Atoms of the same element with different numbers of neutrons

Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Section 2: Chemical Elements

Introduction

Chemical elements are pure substances consisting of only one type of atom. Life depends on a select group of elements.

• Elements of Life (CHNOPS):

  • Carbon (C)

  • Hydrogen (H)

  • Nitrogen (N)

  • Oxygen (O)

  • Phosphorus (P)

  • Sulfur (S)

• Trace elements: Needed in small amounts (e.g., iron, iodine); often act as enzyme cofactors

Section 3: Electronic Configuration

Introduction

The arrangement of electrons in shells around the nucleus determines how atoms interact and bond.

• Electron energy shells: Electrons occupy shells at different energy levels

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

• Atoms seek stable configurations: Usually 2, 8, or 18 electrons in outer shell

Exam Tip: Know which elements form 1, 2, 4, or 8 bonds.

Section 4: Chemical Bonds

Introduction

Chemical bonds are forces that hold atoms together in molecules. The type of bond affects molecular properties and biological function.

• Ionic bonds: Electron transfer between atoms

• Covalent bonds: Electron sharing between atoms

• Polar vs. nonpolar: Covalent bonds can be polar (unequal sharing) or nonpolar (equal sharing)

• Hydrogen bonds: Weak but biologically important; stabilize DNA and proteins

Importance: Bond type affects molecular shape and function.

Section 5: Chemical Reactions

Introduction

Chemical reactions involve the making and breaking of bonds, transforming substances into new products.

• Synthesis: $A + B \rightarrow AB$

• Decomposition: $AB \rightarrow A + B$

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

• Activation energy: Energy needed to start a reaction

Section 6: Water Chemistry

Introduction

Water is essential for life due to its unique properties, including its role as a solvent and its ability to moderate temperature and pH.

• Solvent: Dissolves many substances

• Participates in reactions

• pH scale:

  • Acidic: < 7

  • Basic: > 7

  • Neutral: 7

• Buffers: Resist pH change; critical for enzyme activity

Section 7: Inorganic Compounds

Introduction

Inorganic compounds, such as acids, bases, and salts, play key roles in cellular processes and microbial growth.

• Acids: Release H+

• Bases: Release OH-

• Salts: Dissociate into ions

• Microbiology Link: pH affects microbial growth; some molecules thrive in extreme pH

Section 8: Organic Compounds

Introduction

Organic compounds are carbon-based molecules essential for cell structure, metabolism, and genetic information.

• Carbohydrates: Energy and structure

• Lipids: Membranes, energy storage

• Proteins: Enzymes, structure, transport

• Nucleic acids: Genetic information

The Four Types of Macromolecules

Introduction

Macromolecules are large organic molecules (polymers) made of repeating units (monomers). They are crucial for cell structure, metabolism, and genetic information.

1. Carbohydrates

• Structure: Elements: C, H, O; General formula: $(CH_2O)_n$

• Types:

  • Monosaccharides: glucose, fructose

  • Disaccharides: sucrose, lactose

  • Polysaccharides: starch, glycogen, cellulose

• Functions: Primary energy source, energy storage, structural components

• Microbiology Connections: Polysaccharides form capsules; pathogens use carbohydrates for adhesion

2. Lipids

• Structure: Elements: C, H, O (sometimes P); built from fatty acids + glycerol

• Types:

  • Simple lipids: fats, oils

  • Complex lipids: phospholipids, steroids

• Functions: Cell membrane structure, energy storage, insulation, hormone signaling

• Microbiology Connections: Phospholipid bilayers form plasma membranes; mycoplasma membranes contain cholesterol

3. Proteins

• Structure: Elements: C, H, O, N (sometimes S); built from amino acids joined by peptide bonds

• Levels of Structure:

  • Primary: amino acid sequence

  • Secondary: alpha helix, beta pleated sheet

  • Tertiary: 3D folding

  • Quaternary: multiple polypeptides

• Functions: Enzymes, transport, movement, defense

• Microbiology Connections: Most enzymes are proteins; bacterial toxins are proteins; protein denaturation affects microbial survival

4. Nucleic Acids

• Structure: Elements: C, H, O, N, P; built from nucleotides joined by phosphodiester bonds

• Types:

  • DNA: double-stranded; bases: A-T, C-G

  • RNA: single-stranded; bases: A-U, C-G; types: mRNA, tRNA, rRNA

• Functions: Store genetic information, direct protein synthesis, regulate cell activities

• Microbiology Connections: DNA determines microbial traits; RNA serves as genetic material in many viruses

Quick Comparison Table

Macromolecule	Monomer	Bond	Main Function
Carbohydrates	Monosaccharide	Glycosidic	Energy, structure
Lipids	Fatty acids + glycerol	Ester	Membranes, energy
Proteins	Amino acids	Peptide	Enzymes, structure
Nucleic Acids	Nucleotides	Phosphodiester	Genetic info

Section 9: Enzymes

Introduction

Enzymes are biological catalysts that speed up chemical reactions in cells by lowering activation energy.

• Key Concepts:

  • Enzymes catalyze biological reactions

  • Active site binds substrate

• Factors Affecting Activity:

  • Temperature

  • pH

  • Inhibitors (competitive, noncompetitive)

  • Denaturation

Check Your Understanding – What to Know

• Label an atom

• Identify bond types

• Predict pH changes

• Explain enzyme specificity

• Describe effects of temperature & pH on enzymes

Exam Study Tips

• Focus on definitions and processes

• Understand cause-and-effect

• Practice explaining diagrams in words

• Know why chemistry matters in microbes