Introduction to Eukaryotes

Eukaryotes Introduction

• Eukaryotes have a true nucleus and membrane-bound organelles
• Key characteristics of eukaryotes include:
  • Nucleus
  • Cytoskeleton
  • Membrane-bound organelles (ER, Golgi, lysosomes, vacuoles, peroxisomes, mitochondria, chloroplasts)
  • Asexual reproduction (various methods)
  • Cell walls (in some)
  • Capsules (in some)
  • Binary fission (in some)
  • Cilia or flagella (in some)
  • Linear DNA associated with proteins
  • Larger ribosomes (80S)
  • Larger cell size (>10 μm diameter)
  • Mitosis and meiosis
  • Multicellular forms (in some)

Eukaryote Objectives

• Identify common characteristics of eukaryotes.
• Explain the endosymbiotic theory.
• Describe how multicellular forms may have evolved from protists.

Prokaryote/Eukaryote Comparison

• Prokaryotes lack a nucleus and membrane-bound organelles.
• Eukaryotes have a true nucleus and membrane-bound organelles.
• Both can have cell walls, capsules, binary fission, and be unicellular.

Eukaryote Evolution

• Eukaryotes are thought to have evolved from prokaryotes
• The endosymbiotic theory proposes that mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by a larger cell
• Evidence for endosymbiosis includes:
  • Mitochondria and chloroplasts have their own DNA
  • Mitochondria and chloroplasts have their own ribosomes
  • Mitochondria and chloroplasts divide by binary fission

Kingdom Protista

• Protists are a diverse group of eukaryotic organisms.
• Protists can be plant-like, animal-like, or fungus-like.
• Plant-like protists are photosynthetic (e.g., algae).
• Animal-like protists are heterotrophic (e.g., protozoa).
• Fungus-like protists are decomposers (e.g., slime molds).
• Protists arose from prokaryotes, and their descendants gave rise to all plants, fungi, and animals as well as modern protists.
• Classification is difficult due to the wide diversity of protists.

Classification of Protists

• Protists are classified by their mode of nutrition (plant-like, animal-like, or fungus-like).
• This system is artificial (non-phylogenetic), and the best approach is the traditional system of single kingdom Protista

Plastid Evolution

• Plastids (e.g., chloroplasts) are produced through secondary endosymbiosis.
• Mitochondria arose first then plastids.
• Organisms with plastids (chloroplasts) evolved from photosynthetic prokaryotes engulfed by heterotrophic eukaryotes.

This quiz covers the fundamental characteristics of eukaryotes, including their structure, reproduction methods, and the endosymbiotic theory. You will explore how eukaryotes differ from prokaryotes and the significance of multicellular forms. Test your knowledge on cell biology and the evolution of complex organisms.