bio 2.11

Overview of Cell Compartmentalization

• Cell Types: Two main types of cells are prokaryotic and eukaryotic.
• Plasma Membrane:
  • Both prokaryotic and eukaryotic cells have a plasma membrane which separates their internal environment from the external environment.

Differences Between Prokaryotic and Eukaryotic Cells

• Prokaryotic Cells:

  • Lack internal membrane-bound organelles.
  • Only have the plasma membrane as their boundary.
  • Contain a nucleoid region where their genetic material is located.

• Eukaryotic Cells:

  • Have extensive internal membranes and membrane-bound organelles which compartmentalize cellular functions.
  • The genetic material is housed within a membrane-bound nucleus, a key distinguishing feature.

Evolution of Membrane-Bound Organelles

• Theory of Endosymbiosis:
  • Proposes that mitochondria and chloroplasts originated from free-living prokaryotic cells that were engulfed by an ancestral eukaryotic cell.
  • Initial engulfment of a free-living aerobic prokaryote by an anaerobic eukaryotic cell through endocytosis, resulting in a mutually beneficial relationship.
  • Mitochondrial Evolution:
  • Aerobic proteobacterium engulfed, leading to the development of mitochondria within the eukaryotic cell.
  • Chloroplast Evolution:
  • Free-living photosynthetic prokaryote engulfed, leading to the development of chloroplasts.

Evidence Supporting Endosymbiotic Theory

• Double Membranes: Both mitochondria and chloroplasts have double membranes indicating their prokaryotic origins.

  • These membranes help regulate material passage and maintain homeostasis.

• Circular DNA: Mitochondria and chloroplasts contain their own circular DNA, similar to prokaryotic DNA.

• Ribosomes: Both organelles have ribosomes that are structurally similar to those of prokaryotes, allowing them to synthesize their own proteins.

Argumentation Practice

• AP Exam Question Example:
  • Mitochondria contain DNA and ribosomes similar to prokaryotic cells. What conclusion can be drawn?
  • Correct answer: An ancestral cell likely engulfed anaerobic prokaryotes leading to mutual benefits.

Key Takeaways

• Both prokaryotes and eukaryotes have plasma membranes, but eukaryotes possess additional internal structures that enhance cellular efficiency.
• The theory of endosymbiosis explains how free-living prokaryotes became integral to eukaryotic cells, forming mitochondria and chloroplasts, supported by various lines of evidence.