CHAPTER 5

Chapter Objectives

  • Define the major categories of eukaryotic microbes and invertebrate parasites.

  • Describe the role of fungi in the environment and in human disease.

  • Describe the role of protists in the environment and in human disease.

  • Outline the infectious cycles of eukaryotic parasites.

Eukaryotic Cells Overview

Eukaryotic cells are characterized by their complex structure, which includes a defined nucleus and various membranous organelles. Nearly all eukaryotic cells possess mitochondria, facilitating energy production. These structures allow eukaryotic cells to attain sizes significantly larger than bacterial cells, with some species growing up to a million times larger, while others resemble E. coli in size, being less than 2 µm.

Organelles in Eukaryotic Cells

  • Nucleus: The control center of the cell, housing genetic material.

  • Mitochondrion: The powerhouse of the cell, generating ATP.

  • Golgi Apparatus and Chloroplasts: Involved in processing and energy production respectively.

  • Ribosomes: Essential for protein synthesis.

Reproduction of Eukaryotic Cells

Eukaryotic cells have linear chromosomes that undergo division during mitosis, a process ensuring that each daughter cell inherits a complete set of chromosomes. The unique ends of linear chromosomes necessitate specialized methods of replication, absent in most prokaryotes which contain circular chromosomes. The stages of mitosis include:

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

Asexual vs. Sexual Reproduction

Many eukaryotic microbes can replicate through mitosis, allowing for indefinite proliferation asexually. However, most can also reproduce sexually, involving the exchange of genetic material between different chromosomes and leading to gamete formation. The sexual cycle alternates between diploid (2n) and haploid (n) stages.

  • meiosis is a diverse process because the paired chromosomes go through DNA exchange in order to produces different combos of genetic material for each of the four daughter cells

  • 2 haploids/gametes + fertilization = diploid

Diversity of Microbial Eukaryotes

  • FUNGI IS NOT A PROTIST

Eukaryotic microorganisms can be classified into categories including:

  • Fungi and Microsporidians:

    • tough polysaccharide walls (hard for antibiotics to penetrate)

    • non-motile filaments or yeasts

    • decomposers that get nutrients through absorption

  • Alveolates

    • move with flagellum or cilia

    • free-living, but become parasitic in the body (eg. the bacteria that causes malaria)

  • Amebas: Heterotrophic protists that move using pseudopods and have variable shapes

    • use the ball’s foot to expand its cytoplasm

    • Trypanosomes and Metamonads: Parasitic forms with complex life cycles.

  • Algae: These photosynthetic protists include organisms conducting photosynthesis and can be unicellular or multicellular.

  • Arthropods and Helminths: Multicellular organisms such as insects and worms that can be free-living or parasitic, significantly impacting human health.

    • BUGS AND WORMS ARE NOT TRUE MICROBES

      • you may need a microscope to see them, though

  • TYPES OF UNICELLULAR EUKARYOTES

    1) protozoans = animal-like

    2) algae = plant-like

  • slime molds = fungi-like

Protist Motility

  1. Paramecium moves with cilia

  2. Euglena moves with flagellum

  3. amoeba moves with pseudopods

Eukaryotic Infectious Agents

  1. Fungi and Microsporidians: Some are asexual, alternating between diploid and haploid forms; they develop into gametes under stress for sexual reproduction.

  2. Alveolates: Exhibit flagella or cilia for movement, including notable parasites like Plasmodium (causing malaria).

  3. Helminths: Include roundworms and flatworms, with varying life cycles often requiring intermediate hosts for completion.

  4. Algae: Critical to oxygen production, can lead to algal blooms.

Fungi Characteristics

  • asexual or sexual

  • WHEN FOOD IS LIMITED, HAPLOIDS MAY DEVELOP INTO GAMETES AND MATE

  • dimorphic fungi grow at different levels when in environments with different temperatures

    • Histoplasma capsulatum

      • outdoors = mycelium

      • once it is inhaled into the body (optimal temperature for growth), yeast is produced in response, causing a lung infection

Algae and Their Importance

Algae are autotrophic organisms crucial for oxygen production, being responsible for approximately 70% of the Earth's oxygen supply. Diverse types include both unicellular and multicellular forms and can contribute to phenomena like algal blooms/red tides, which is when overgrown algae release neurotoxins that can negatively effect humans