Introduction

• Welcome and acknowledgment of the rain and its significance in Davis.

Overview of Today's Topics

• Continue discussion on microbial eukaryotes.

• Finish concept of endosymbiotic origin of mitochondria and chloroplasts.

• Introduction to practical examples in upcoming lectures.

Endosymbiotic Origin of Mitochondria

Mechanism of Cell Ingestion

• Importance of understanding how cells can merge without leaking internal contents.

• Scanning Electron Micrograph of Amoeba:

  • Provides a 3D view that aids comprehension of cell interactions.

• Cells cannot simply create a hole in the membrane to ingest material; this would lead to lysis.

Endocytosis

• Definition: Bringing substances into a cell without leaking cellular contents.

• **Process:

  1. Cell membrane creates a depression.

  2. Depressed membrane wraps around the invader (item).

  3. Membrane reforms, creating a bubble that contains the item.**

• Endocytosis forms a membrane-bound 'bubble' containing the ingested item.

Phagocytosis

• A form of endocytosis for larger particles.

• Process:

  • The cell membrane rises and engulfs larger particles rather than forming a depression.

  • Results in creation of a membrane-wrapped vesicle around the engulfed particle.

Lynn Margulis and Serial Endosymbiosis

• Proposed that organelles like mitochondria originated through endocytosis/phagocytosis.

• Initially rejected idea, later gained support through accumulated evidence.

• Key Contribution: The partnership of prokaryotes inside eukaryote cells resulted in the evolution of complex cells.

Membrane Architecture and Cell Theory

• Both endocytosis and phagocytosis provide membrane wrappers around engulfed materials.

• Mitochondria contain multiple membranes indicative of their prokaryotic ancestry.

Archaeon Host Theories

• Current theories about mitochondrial origins involvement: Loki archaeota.

• Issues highlighted include membrane lipid differences between archaea and eukaryotes.

• Two hypotheses regarding eukaryotic host cell origins:

  1. Bacterial-made membranes: If eukaryotic membranes were formed by bacteria.

  2. Diverse Archaeon: Potential existence of archaea with eukaryotic-type lipid membranes.

Clicker Questions

• Gram Negative Bacteria: Understand layer structure affecting engulfment during endocytosis.

• Mitochondrial Characteristics: Reproduce like bacteria (haploid DNA) through binary fission, mutations occur during division.

Endosymbiotic Origin of Chloroplasts

• Chloroplasts' origin traced back to cyanobacteria, which perform oxygenic photosynthesis.

• Phylogenetic evidence supports cyanobacteria as ancestors of chloroplasts.

• Importance of Cyanobacteria: Role in modifying the atmosphere and evolution of life.

Double Membrane Structure in Chloroplasts

• Internal membrane structure of chloroplasts mimics characteristics of their prokaryotic ancestors.

• Example: Synechococcus is a modern cyanobacterium still exhibiting internal membranes.

Implications of Chloroplasts and Mitochondria

• Chloroplasts and mitochondria share features that indicate their prokaryotic origins:

  • Multiple membranes, haploid circular DNA.

• Their evolutionary significance is essential to the understanding of complex eukaryotic cell development.

Final Thoughts on Symbiogenesis

• Photosynthetic eukaryotes post-primary endosymbiosis may have engulfed advanced algal cells leading to tertiary endosymbiosis.

• Genetic transfer and cellular modifications contribute to cellular diversity and adaptability.

Connections to Human Biology

• Importance of understanding these mechanisms broadens applications in medicine and drug design.

• Example: Hydrogenosomes as drug targets in parasitic infections (e.g., Trichomonas vaginalis).

Conclusion

• Future lectures will explore applications and implications of the discussed concepts in the context of disease and treatment.