Overview
This lecture covers the evolution and diversity of eukaryotic cells, examines fungal, protist, and helminth organisms, and details their structures, lifecycles, and medical relevance.
Evolution and Features of Eukaryotes
- Eukaryotes, bacteria, and archaea evolved from the last common ancestor (LCA).
- The LCA was neither prokaryotic nor eukaryotic, but gave rise to all three domains.
- Endosymbiosis: Organelles such as mitochondria and chloroplasts evolved from bacteria-like cells being engulfed.
- Eukaryotes can be unicellular or multicellular; examples include fungi (both), protozoa (unicellular), and helminths (multicellular).
- Tissues are groups of similar cells; organs are groups of tissues performing functions.
Eukaryotic Cell Structure
- Common organelles: nucleus, mitochondria, ER, Golgi apparatus, vacuoles, cytoskeleton, glycocalyx.
- Some eukaryotes also have a cell wall, locomotor appendages, or chloroplasts.
- Eukaryotic flagella are thicker, complex, and move with a whipping motion (9+2 microtubule arrangement).
- Cilia are shorter, more numerous, used for movement and feeding.
- The glycocalyx is a protective, sugar-based coating aiding attachment and preventing desiccation.
- Fungi and algae have rigid cell walls; fungal walls often made of chitin or cellulose.
- Eukaryotic membranes are phospholipid bilayers with sterols, selectively permeable.
Eukaryotic Internal Structures and Functions
- Nucleus: DNA storage, nucleolus for rRNA synthesis.
- ER: rough (with ribosomes, protein transport) and smooth (lipid synthesis).
- Golgi apparatus modifies and packages proteins.
- Lysosomes (digestive enzymes) and vacuoles (storage).
- Mitochondria generate ATP, contain circular DNA, 70S ribosomes.
- Chloroplasts enable photosynthesis.
- Cytoskeleton: actin filaments, intermediate filaments, microtubules for shape and transport.
- Eukaryotic ribosomes: 80S (large 60S, small 40S subunits).
Fungi (Kingdom Myceteae)
- Macroscopic (mushrooms) and microscopic fungi (molds, yeasts).
- All fungi are heterotrophic; some are saprobes (decomposers), others parasites.
- Yeasts reproduce asexually by budding; molds form hyphae and mycelium.
- Fungal spores (sporangiospores, conidiospores) produced sexually or asexually.
- Fungi can benefit (decomposition, antibiotics) or harm (disease, allergies) humans.
Protists: Algae and Protozoa
- Algae: unicellular, photosynthetic, primary oxygen producers, some produce toxins (red tide).
- Protozoa: unicellular, heterotrophic, use flagella, cilia, or pseudopods for movement.
- Life stages include trophozoite (active) and cyst (dormant, resistant).
- Some are pathogenic (e.g., Plasmodium-malaria, Trypanosoma-sleeping sickness).
- Reproduce by mitosis or conjugation (genetic exchange).
Helminths
- Two major groups: flatworms (Platyhelminthes—tapeworms, flukes) and roundworms (Nematoda).
- Life cycle: egg → larva → adult; both egg and larva can be infectious.
- Most developed system is reproductive.
- Hermaphroditism is common; some species produce millions of eggs.
- Classification by body type, organs, and life cycle; diagnosis by microscopic identification.
Key Terms & Definitions
- Endosymbiosis — Theory that certain organelles evolved from engulfed bacteria.
- Glycocalyx — Sticky, protective sugar coating outside cell membrane.
- Hyphae — Threadlike fungal cells forming mycelium.
- Trophozoite — Active, feeding stage of protozoa.
- Cyst — Dormant, resistant protozoan stage.
- Saprobes — Fungi that feed on dead organic matter.
- Hermaphroditic — Having both male and female reproductive organs.
Action Items / Next Steps
- Review organelle functions and differences between cell types.
- Study life cycles of fungi, protozoa, and helminths.
- Complete assigned readings on eukaryotic microorganisms and their medical relevance.