Endosymbiotic Theory

Summary

This video explains the endosymbiotic theory, which describes how eukaryotic cells evolved from simpler prokaryotic cells. The theory suggests that mitochondria and chloroplasts were once independent prokaryotic cells that were engulfed by larger cells through endocytosis, forming symbiotic relationships. Evidence supporting this includes the double membranes and circular DNA found in both organelles. The video also covers how the first eukaryotic cells developed into modern animal and plant cells, with mitochondria providing energy and chloroplasts contributing to photosynthesis.

Takeaways

• 😀 The endosymbiotic theory explains the transition from prokaryotic cells to eukaryotic cells.
• 😀 Prokaryotic cells are simpler, lacking a nucleus, and contain only DNA, ribosomes, and a cell membrane.
• 😀 The infolding of the plasma membrane during endocytosis led to the formation of structures like the nuclear membrane and endoplasmic reticulum.
• 😀 The mitochondria likely originated from an aerobic, heterotrophic prokaryote engulfed by a larger cell through phagocytosis.
• 😀 Mitochondria's two membranes support the theory of it being a once-independent cell engulfed by a larger one.
• 😀 Mitochondria also contain circular DNA, which is characteristic of prokaryotic cells, not eukaryotic cells.
• 😀 The relationship between the host cell and the engulfed prokaryote became symbiotic, with the larger cell receiving ATP and the smaller one receiving protection.
• 😀 Plant cells evolved from early animal cells, inheriting mitochondria from the symbiotic relationship.
• 😀 Plant cells also acquired a photosynthetic prokaryote, which later evolved into chloroplasts within the cell.
• 😀 Chloroplasts, like mitochondria, have two membranes and contain their own circular DNA, further supporting the endosymbiotic theory.

Q & A

What is the endosymbiotic theory?

The endosymbiotic theory explains how eukaryotic cells evolved from prokaryotic cells through the engulfment of prokaryotes by a larger host cell. Over time, these engulfed prokaryotes formed symbiotic relationships with the host cells, eventually becoming organelles like mitochondria and chloroplasts.

How does the infolding of the plasma membrane contribute to the formation of eukaryotic cells?

The infolding of the plasma membrane during endocytosis leads to the formation of structures like the nuclear membrane and the endoplasmic reticulum. The plasma membrane is made of phospholipids, the same material used in the nuclear membrane and the endoplasmic reticulum, making this infolding process a plausible explanation for their origin.

What role does the mitochondrion play in the endosymbiotic theory?

Mitochondria are believed to have once been independent aerobic heterotrophic prokaryotic cells. These cells were engulfed by a larger cell through phagocytosis and instead of being digested, they formed a symbiotic relationship with the host cell, providing it with ATP in exchange for protection.

What evidence supports the idea that mitochondria were once independent prokaryotic cells?

Two key pieces of evidence support this idea: first, mitochondria have two membranes, the inner membrane likely being acquired when the prokaryote was engulfed. Second, mitochondria have their own circular DNA, similar to the DNA found in prokaryotes, unlike the helical DNA found in eukaryotic cells.

Why is the circular DNA in mitochondria significant to the endosymbiotic theory?

The circular DNA in mitochondria is significant because it mirrors the structure of DNA found in prokaryotic cells. This suggests that mitochondria were once free-living prokaryotes, which supports the idea of their engulfment and eventual symbiosis with the host cell.

What is mutualism in the context of endosymbiosis?

Mutualism is a type of symbiosis where both organisms benefit from the relationship. In the case of mitochondria, the larger host cell gains ATP, while the smaller engulfed cell (the mitochondrion) receives protection from the host cell.

How does the process of endocytosis contribute to the formation of eukaryotic cells?

Endocytosis involves the cell engulfing external particles. This process leads to the formation of organelles like the nuclear membrane, endoplasmic reticulum, mitochondria, and chloroplasts. The engulfed organisms evolve into symbiotic organelles that serve essential functions within the eukaryotic cell.

What is the significance of chloroplasts in plant cells according to the endosymbiotic theory?

Chloroplasts are believed to have evolved in a similar way to mitochondria. They were once photosynthetic prokaryotes that were engulfed by an early eukaryotic cell. Over time, chloroplasts became an integral part of the plant cell, providing sugar and oxygen through photosynthesis in exchange for protection.

How does the process of engulfing photosynthetic prokaryotes lead to the formation of chloroplasts?

When a photosynthetic prokaryote is engulfed by an early eukaryotic cell, it cannot be digested and instead forms a symbiotic relationship with the host. Over time, this photosynthetic prokaryote evolves into a chloroplast, providing the host cell with sugars and oxygen as a byproduct of photosynthesis.

What are the two pieces of evidence that support the idea of chloroplasts originating from engulfed prokaryotes?

Similar to mitochondria, chloroplasts have two membranes: the inner membrane inherited from the engulfed prokaryote and the outer membrane from the host cell. Additionally, chloroplasts contain their own circular DNA, further suggesting their prokaryotic origin.