CLASS 4 SIMPLE

Class Overview

  • MBIO*1220 - Essentials of Microbiology

Learning Outcomes

  • Differentiate between prokaryotes and eukaryotes.
  • Identify and describe bacterial cell structures.

Bacterial Cell Wall

  • Semi-rigid structure providing shape; protects against rupture.
  • Used in bacterial identification (e.g., Gram stain).
  • Composed of peptidoglycan: polysaccharide (NAG & NAM) + peptide chains.

Gram-Positive Cell Wall

  • Thick peptidoglycan layer outside the plasma membrane.
  • Contains teichoic acids (wall and lipoteichoic).
  • One membrane present (cytoplasmic membrane).

Gram-Negative Cell Wall

  • Thin peptidoglycan layer between two membranes.
  • Outer membrane consists of lipids, proteins, LPS.
  • LPS's lipid portion is toxic (endotoxin).

Gram Stain Mechanism

  • Gram-positive: crystal violet retained (purple).
  • Gram-negative: crystal violet washed away (pink with safranin counterstain).

Importance of Peptidoglycan

  • Unique to bacteria; target for antibiotics (e.g., penicillin).
  • Degraded by lysozyme, a natural defense.

Cytoplasmic Membrane

  • Composed of phospholipid bilayer; semi-permeable barrier.
  • Disrupted by alcohols (antimicrobial agent).

Internal Components

  • Cytoplasm: 80% water; contains nutrients, enzymes, and structures.
  • Nucleoid: Contains bacterial chromosome (DNA); may have plasmids.
  • Ribosomes: Sites for protein synthesis; 70S ribosomes differ from 80S in eukaryotes.
  • Storage Granules: Nutrient deposits (e.g., sulfur, glycogen).
  • Endospores: Durable, dormant structures formed by some Gram-positive bacteria.

Sporulation Process

  1. DNA replication.
  2. Septum formation.
  3. Engulfing of smaller compartment.
  4. Spore coat formation.
  5. Release of spore as mother cell dies.

Eukaryotic Cell Structure

  • More complex than prokaryotes; includes nucleus and membrane-bound organelles.
  • Cytoplasmic membrane similar; often includes sterols.
  • Cell wall not present in all eukaryotes (plant cell walls: cellulose; fungal: chitin).

Cytoplasm in Eukaryotes

  • Contains cytoskeleton for support and transport; larger ribosomes (80S).

Membrane-Bound Organelles

  • Differences from prokaryotes: nucleus, mitochondria, chloroplasts.

Eukaryotic Appendages

  • Cilia and flagella for movement; whip-like motion.

Summary

  • Differentiation of prokaryotic and eukaryotic cells.
  • Identification of bacterial structures covered in class.
  • Next class focus: dynamics of microbial growth (Chapter 4). Midterm on October 14th.