Bacteria Simplified: Structure, Function & Classification Made Easy

📘 Chapter 2: Bacteria and Viruses – Easy Notes

🔸 Introduction to Classification

Over the years, many systems were proposed to classify organisms.
Robert H. Whittaker introduced the Five-Kingdom Classification System:
Monera, Protista, Fungi, Plantae, and Animalia.

• Kingdom Monera includes all prokaryotes (organisms without a true nucleus).
• The rest (Protista, Fungi, Plantae, Animalia) include eukaryotes (organisms with a true nucleus).

🔸 Three-Domain System

Due to new molecular studies (research at the DNA/protein level), flaws were found in the five-kingdom system.
Most biologists now support the Three-Domain System.

• Domain Bacteria includes prokaryotic organisms we call bacteria.

🦠 2.1 – Structure of Bacteria

Bacteria are:

• Unicellular (made of one cell)
• Prokaryotic (no membrane-bound organelles or nucleus)
• Have simplest cellular structure

🔍 Learning Objectives

By the end of the chapter, you should be able to:

• Draw & label a generalized bacterial cell
• Describe structure & chemical composition of:

1. Cell wall, cell membrane, cytoplasm, flagella, capsule

• Explain:

• Endospore formation (helps survival in tough conditions)
• Motility in bacteria (movement using flagella)
• Role of bacteria in nature (recyclers)

• Ecological & eco

🧫 Structure of a Generalized Bacterium

🔹 Cell Wall

• Found outside the plasma membrane
• Made of peptidoglycan or murein (glycan = sugar chain, peptide = small protein chains)
• Provides rigidity and shape

➤ Types of Cell Walls

1. Gram-Positive Bacteria:

• Thick peptidoglycan layer
• Low lipid content
• Retains violet dye → appears purple

1. Gram-Negative Bacteria:

• Thin peptidoglycan layer
• Has an outer membrane made of lipopolysaccharides (fat + sugar) and lipoproteins
• Contains porins (proteins acting as channels)
• Has larger periplasmic space (area between membrane & peptidoglycan)
• More resistant to antibiotics

💡 Gram staining technique was devised by Hans Christian Gram

🔹 Capsule

• Gelatinous (jelly-like) layer outside the cell wall
• Makes colonies sticky and helps in protection

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🧬 Cell Membrane (Plasma Membrane)

• Lies beneath the cell wall
• In bacteria without a cell wall (like Mycoplasma), it is the outermost layer
• Lacks sterols (like cholesterol)
• Forms internal folds called mesosomes (used in DNA replication, cell division, and respiration)

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💧 Cytoplasm & Genetic Material

• Contains nucleoid, ribosomes, and mesosomes
• No cytoskeleton, no membrane-bound organelles
• Ribosomes are small: sediment at 70S (with 50S + 30S subunits)

🔹 Nucleoid

• Region where DNA is located
• DNA is circular, double-stranded, and without histones
• Acts like the bacterial chromosome

🔹 Plasmids

• Small, circular DNA separate from nucleoid
• Self-replicating
• Carry resistance genes (e.g., against antibiotics)
• Used in genetic engineering as vectors (DNA carriers)

💡 Plasmids help in cloning and synthesis of specific proteins

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🧠 Quick Recap – Key Terms Explained

• Prokaryote: Cell without true nucleus or organelles
• Eukaryote: Cell with true nucleus and organelles
• Peptidoglycan: Sugar + protein structure in bacterial cell wall
• Gram Staining: Dye test to identify bacteria type
• Mesosome: Folded part of cell membrane inside cytoplasm
• Plasmid: Extra DNA in bacteria, often used in biotech
• Porin: Protein channel in bacterial outer membrane
• Periplasmic Space: Space between membrane and cell wall
• Normal Flora: Good bacteria naturally living in the human body

1. enomic importance

2. Use of bacteria in research

3. Normal flora (bacteria naturally living in humans)

4. Benefits of normal flora

5. Structure of bacteriophage and HIV

• Class Mammalia
• Viruses& Clasification
• Biodiversity And Measurements
• Species and Speciation
• EXERCISE