Lecture Notes: Theories in Science and Endosymbiotic Theory

Understanding Scientific Theories

Scientific theory differs from the everyday use of the word 'theory'.
- It's not an educated guess.
- It's an explanation of events, supported by scientific evidence.
- Must be testable and repeatedly tested.
- Theories can change or be disproven, but they are backed by facts.

Explains the evolution of eukaryote cells from prokaryote cells.
Prokaryotes vs. Eukaryotes
- Prokaryotes: No nucleus, no membrane-bound organelles.
- Eukaryotes: Have a nucleus and membrane-bound organelles.
- Commonalities: Both have a cell membrane, cytoplasm, ribosomes, genetic material.
Historical Context
- Over 2 billion years ago, a variety of prokaryotes existed.
- Some prokaryotes had photosynthetic abilities, others could use oxygen to produce ATP, and some were capable of engulfing other cells.

Larger prokaryotic cells engulfed smaller bacteria.
- Small bacteria weren't digested but lived as symbionts.
- These became the ancestor heterotroph eukaryote cells.
- Eventually, cells engulfed photosynthetic bacteria leading to ancestor autotroph eukaryotes.
Evolutionary Impact
- Bacteria that used oxygen evolved into mitochondria.
- Bacteria that used sunlight evolved into chloroplasts.
- Mitochondria likely developed before chloroplasts as almost all eukaryotic cells have mitochondria.

Mitochondria and chloroplasts have their own separate DNA.
- DNA arrangement is similar to bacterial DNA.
Size of mitochondria and chloroplasts are comparable to bacteria size.
Both can independently divide in a manner similar to bacteria.

Endosymbiotic theory provides a framework for understanding the evolution of modern eukaryotes from prokaryotes.
Encourages further exploration of related concepts like secondary endosymbiosis.

Stay curious!