Understanding Cell Theory and Structure

Jan 30, 2025

Okay, here's the updated version of your notes including a table summarizing information on filamentous appendages (flagella):

Lecture Notes: Chapter 3 - The Cell

Introduction

  • Focus on cell structures and comparison between eukaryotic and prokaryotic cells
  • Overview of early cell theories and modern theories like cell theory and endosymbiotic theory

Early Theories and Scientists

  • Spontaneous Generation: Early belief that life arises from nonliving matter
    • Aristotle: Vital heat; early (incorrect) theory of life's origin.
    • John Baptiste van Helmont: Mice from rags & wheat; flawed experiment, highlighting need for controlled studies.
    • Francesco Redi: Maggots from meat; controlled experiment disproving spontaneous generation.
    • John Needham & Lazzaro Spallanzani: Contrasting broth experiments; Spallanzani improved methodology, closer to refuting spontaneous generation.

Modern Cell Theory

  • All cells come from pre-existing cells
  • Cells are the fundamental units of life
  • Key Contributors:
    • Robert Hooke: First to observe and name cells.
    • Matthias Schleiden: All plants are made of cells.
    • Theodor Schwann: All animals are made of cells; unified plant and animal cell theory.
    • Rudolf Virchow: "Omnis cellula e cellula"—all cells from pre-existing cells.

Endosymbiotic Theory

  • Proposes mitochondria and chloroplasts were once free-living bacteria engulfed by a host cell
  • Evidence: Similarities in DNA and ribosomes between mitochondria/chloroplasts and bacteria
  • Key Contributors:
    • Konstantin Mereschkowski: Chloroplasts from symbiotic bacteria.
    • Ivan Wallin: Cytological evidence supporting endosymbiosis; later confirmed genetically.

Germ Theory of Disease

  • Diseases are caused by microorganisms
  • Key figures and their contributions: (See Table below)

Case Study

  • Barbara, a 19-year-old with pneumonia-like symptoms, treated with amoxicillin
  • Differentiating bacterial, viral, and other pathogen causes

Unique Characteristics of Prokaryotic Cells

  • All cells have cytoplasm, plasma membrane, chromosomes, and ribosomes
  • Prokaryotic cell differences:
    • No membrane-bound nucleus
    • Single circular chromosome
    • Lack of membrane-bound organelles
  • Common Shapes: Coccus, Bacillus, Vibrio, Spirillum

Cell Wall and Structures

  • Gram-positive: Thick peptidoglycan layer, contains teichoic acids, mycolic acid in some
  • Gram-negative: Thin peptidoglycan layer, outer membrane with lipopolysaccharides, periplasmic space
  • Archaea: Pseudo-peptidoglycan or other structural proteins

Plasma Membrane and Transport

  • Passive Transport: Diffusion, osmosis, facilitated diffusion (no energy)
  • Active Transport: Requires ATP, moves substances against gradient

Endospores

  • Formed by some gram-positive bacteria under stress
  • Resistant to harsh conditions
  • Examples:
    • Bacillus anthracis (anthrax)
    • Clostridium tetani (tetanus)
    • Clostridium difficile (C. difficile, pseudomembranous colitis)
    • Clostridium perfringens (gas gangrene)
    • Clostridium botulinum (botulism)

Appendages

  • Fimbriae and Pili: Aid in attachment, DNA transfer
  • Flagella:

| Arrangement | Description | Example Species | Disease Caused | |-----------------|----------------------------------------------|-----------------------------|-------------------------------------------| | Monotrichous | Single flagellum at one end | Vibrio cholerae | Cholera | | Amphitrichous | Single flagellum at both ends | Spirillum species | Spirillosis (various species, various symptoms) | | Lophotrichous | Tuft of flagella at one end | Pseudomonas aeruginosa | Various opportunistic infections | | Peritrichous | Flagella covering the entire bacterial surface | Escherichia coli (some strains) | Various, including gastroenteritis |

  • Types of Movment: positive,toward & negative,away
  • Phototaxis - light
  • Magnetotaxis - Magnetic
  • Chemotaxis - chemical

Clinical Case Study Conclusion

  • Considering resistance, viral causes, or broader antibiotic treatment

Prokaryotic Inclusion Bodies

| Inclusion Body Type | Description | Example(s) | |----------------------------|---------------------------------------------------------------------------------|-------------------------------------------------| | Volutin Granules (Metachromatic Granules) | Store polymerized inorganic phosphate; used in metabolism and biofilm formation | Corynebacterium diphtheriae | | Sulfur Granules | Store elemental sulfur; used in sulfur bacteria metabolism | Thiobacillus species | | Polyhydroxybutyrate (PHB) | Stores carbon; used in biodegradable plastics production | Bacillus species, Pseudomonas species | | Gas Vacuoles | Contain gas; adjust buoyancy in aquatic prokaryotes | Many aquatic prokaryotes | | Magnetic Inclusions | Contain magnetosomes; align along magnetic fields | Various magnetotactic bacteria | | Carboxysomes | Contain Rubisco; involved in carbon metabolism | Various photosynthetic bacteria and cyanobacteria |

Cell Envelope and Glycocalyx

  • Glycocalyx: External sugar coat aiding attachment, biofilm formation, and protection. A well-organized glycocalyx is called a capsule; Streptococcus pneumoniae is an example of a bacterium with a capsule that contributes to its pathogenicity. A less organized glycocalyx is called a slime layer.
  • Capsule: Highly organized glycocalyx; contributes to pathogenicity (e.g., Streptococcus pneumoniae). Provides protection from phagocytosis by immune cells.

Germ Theory of Disease Key Figures

| Scientist | Contribution | |------------------------|------------------------------------------------------| | Girolamo Fracastoro | Early suggestion of disease transmission methods. | | Ignaz Semmelweis | Handwashing reduces puerperal fever. | | John Snow | Cholera outbreak source tracing; epidemiology. | | Louis Pasteur | Microorganisms cause fermentation & disease; refuted spontaneous generation. | | Joseph Lister | Antiseptic surgical techniques. | | Robert Koch | Koch's postulates; linking microbes to specific diseases. |

This study guide covers key concepts and theories discussed in the lecture on Chapter 3, focusing on the cell, its structure, and associated theories. It includes important historical experiments that shaped modern understanding of biology and disease.