In-Depth Notes on Eukaryotic Cells and Microorganisms

Overview of Eukaryotes

• Learning Outcomes:
  • Relate bacterial, archaeal, and eukaryotic cells to the last common ancestor.
  • List types of eukaryotic microorganisms (unicellular vs. multicellular).
  • Explain the role of endosymbiosis in the development of eukaryotic cells.

The History of Eukaryotes

• Eukaryotic cells first appeared ~4 billion years ago.
• Bacteria and eukaryotes evolved from a precursor known as the last common ancestor (LCA):
  • The LCA was neither prokaryotic nor eukaryotic.
  • Gave rise to bacteria, archaea, and eukarya.
• Organelles: Originated from primitive cells trapped in eukaryotic cells.

Endosymbiotic Organelles

• Organelles like mitochondria and chloroplasts likely originated through a process of endosymbiosis.
  • Bacterial or archaeal cells became engulfed by another LCA descendant, becoming permanent parts of that cell.
• Evidence for endosymbiosis:
  • Mitochondria and chloroplasts have their own (circular) DNA.
  • They contain 70S ribosomes.
  • Double-layer membranes.

Eukaryotic Organisms in Microbiology

• Types:
  • Protozoa: Always unicellular.
  • Fungi: Unicellular (yeasts) or multicellular (molds).
  • Algae: Unicellular or multicellular.
  • Helminths: Multicellular but have unicellular egg or larval forms.

Features of Eukaryotic Cells

• Common Features:
  • Cytoplasmic membrane, nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, vacuoles, cytoskeleton, and glycocalyx.
• Some Eukaryotic Cells Include:
  • Cell wall, locomotor appendages, chloroplasts.

Flagella vs. Cilia

• Flagella:
  • 10× thicker than bacterial flagella, structurally complex, covered by the cell membrane, and exhibit a 9+2 microtubule arrangement.
  • Function via a whipping motion.
• Cilia:
  • Shorter and more numerous than flagella.
  • Found in certain protozoa and animal cells, used for feeding and movement.

Cytoplasmic Membrane

• Structure: A bilayer of phospholipids with embedded proteins and sterols.
• Function: Selectively permeable, allowing nutrient transport and waste removal.

Nucleus

• Control center of the cell, separated from the cytoplasm by a nuclear envelope.
• Contains nucleolus for ribosomal RNA synthesis.

Endoplasmic Reticulum (ER)

• Microscopic tunnels for transport and storage:
  • Rough ER: Has ribosomes, involved in protein synthesis.
  • Smooth ER: Lacks ribosomes, synthesizes nonprotein molecules.

Golgi Apparatus

• Site of protein modification and transport.
• Forms vesicles for storage or secretion.

Mitochondria

• Energy producers of the cell, contain circular DNA and 70S ribosomes, divide independently of the cell.
• Characteristics support the endosymbiotic theory.

Chloroplasts

• Photosynthesis machinery, transform sunlight into chemical energy, producers of oxygen gas.

Ribosomes

• Sites of protein synthesis, consist of 80S ribosomes (60S and 40S subunits).

Cytoskeleton

• Functions include anchoring organelles, enabling shape changes, and facilitating movement.
• Three main types: actin filaments, intermediate filaments, and microtubules.

Fungi

• Approximately 3 to 4 million species split into two groups: macroscopic (mushrooms, puffballs) and microscopic (molds, yeasts).
• Hyphae: long, threadlike cells in molds, can have a dimorphic nature.
• Nutritional Sources: Decomposers, play essential roles in nutrient cycling.
• Pathogenic fungi can lead to community-acquired infections, hospital-associated infections, or opportunistic infections.
• Beneficial Impacts: Decomposition, stable associations with plants, production of antibiotics, and food products.

Algae and Protozoa

• Algae: Photosynthetic organisms with chlorophyll; play key roles as primary producers.
• Protozoa: Diverse group; some are pathogenic, leading to significant health issues in humans.

Helminths

• Include flatworms (cestodes & trematodes) and roundworms (nematodes).
• Transmission routes: food, soil, water, or penetration of the skin.
• Life cycles vary; many have complex developmental stages.

Summary of Eukaryotic Complexity