Question

Reflect and Apply Mitochondria and chloroplasts contain some DNA, which more closely resembles prokaryotic DNA than (eukaryotic) nuclear DNA. Use this information to suggest how eukaryotes may have originated.

Short answer

The similarity of mitochondrial and chloroplast DNA to prokaryotic DNA suggests that eukaryotes originated from a symbiotic relationship between prokaryotic cells.

Step-by-step solution

Understand the Background

Recognize that mitochondria and chloroplasts are organelles within eukaryotic cells known for their role in energy production and photosynthesis respectively. These organelles also contain their own DNA, which is similar to prokaryotic DNA.

Evaluate the DNA Similarity

Note the key point that the DNA found in mitochondria and chloroplasts is more similar to prokaryotic DNA than to eukaryotic nuclear DNA. Prokaryotic DNA is typically circular and much simpler compared to the linear and complex structure of eukaryotic nuclear DNA.

Consider the Endosymbiotic Theory

Introduce the endosymbiotic theory which suggests that eukaryotic cells originated through a symbiotic relationship between early prokaryotic cells. According to this theory, ancestral prokaryotic cells were engulfed by a host cell and eventually became integral parts of the host, evolving into mitochondria and chloroplasts.

Analyze the Evidence

Reflect on the evidence provided by the DNA similarities. The resemblance of the DNA to prokaryotic DNA supports the idea that these organelles originated from prokaryotic cells that were taken inside a host cell.

Formulate a Conclusion

Use the information gathered to conclude that the presence of prokaryotic-like DNA in mitochondria and chloroplasts supports the theory that eukaryotic cells may have originated through the incorporation of prokaryotic cells via endosymbiosis.

Key concepts

mitochondria DNA

Mitochondria are the powerhouse of the cell, famously known for their role in energy production. Interestingly, mitochondria have their own DNA, which is quite unique. Unlike the nuclear DNA found in the cell's nucleus, mitochondrial DNA is circular and resembles prokaryotic DNA. This similarity is crucial as it provides insight into the evolutionary history of cells. By understanding mitochondrial DNA, we can infer that mitochondria may have originated from an ancient prokaryotic cell that entered into a symbiotic relationship with a host cell.

chloroplast DNA

Chloroplasts are the organelles responsible for photosynthesis in plant cells. Like mitochondria, chloroplasts also contain their own DNA. This DNA is also circular and shares a closer resemblance to prokaryotic DNA than to eukaryotic nuclear DNA. The presence of chloroplast DNA supports the endosymbiotic theory, suggesting that chloroplasts may have originated from photosynthetic prokaryotes. This theory posits that these photosynthetic prokaryotes were engulfed by a host cell and, over time, evolved into the chloroplasts we see today.

prokaryotic DNA

Prokaryotic DNA is typically simpler and circular, in contrast to the more complex, linear DNA found in eukaryotic cells. This simpler structure is seen in the DNA of mitochondria and chloroplasts. Understanding the characteristics of prokaryotic DNA helps illuminate the mechanisms behind the endosymbiotic theory. The DNA similarity between prokaryotes and these organelles suggests that ancient prokaryotic cells were the ancestors of mitochondria and chloroplasts, reflecting a pivotal moment in the evolution of eukaryotic cells.

eukaryotic cells

Eukaryotic cells are complex cells characterized by the presence of a nucleus and other membrane-bound organelles. The origin of these cells is a central question in biology. The presence of mitochondria and chloroplasts—organelles with their own prokaryotic-like DNA—within eukaryotic cells is a strong piece of evidence supporting the endosymbiotic theory. Eukaryotic cells likely evolved when early prokaryotic cells entered into symbiotic relationships with host cells, leading to the complex cells we see today.

organelle origins

The origins of organelles such as mitochondria and chloroplasts are best explained by the endosymbiotic theory. According to this theory, mitochondria and chloroplasts originated from once free-living prokaryotic cells. These prokaryotic cells were engulfed by early eukaryotic cells and established a mutually beneficial relationship. Over time, the engulfed cells evolved into permanent organelles, providing energy (mitochondria) or carrying out photosynthesis (chloroplasts) within the host cell. The prokaryotic DNA found in these organelles serves as compelling evidence for this evolutionary process.