Question

What existing evidence supports the theory that mitochondria are of prokaryotic origin?

Short answer

Genetic similarities, prokaryotic-like ribosomes, binary fission, and double membranes provide evidence for the prokaryotic origin of mitochondria.

Step-by-step solution

Understand Endosymbiotic Theory

The endosymbiotic theory suggests mitochondria originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells. This symbiotic relationship evolved into the mitochondria present in modern eukaryotic cells.

Analyze Genetic Evidence

Mitochondria have their own DNA, which is circular and similar to the DNA of prokaryotes. This supports the idea that mitochondria originated from prokaryotic cells.

Compare Ribosomes

Mitochondria contain ribosomes that resemble those found in prokaryotes, both in structure and function. This is another piece of evidence supporting their prokaryotic origin.

Examine Binary Fission

Mitochondria replicate through binary fission, a process characteristic of prokaryotes, not eukaryotic cells, reinforcing their origin from prokaryotic ancestors.

Look at Double Membranes

Mitochondria have a double membrane, consistent with the engulfing mechanism postulated by the endosymbiotic theory, suggesting a prokaryotic origin.

Key concepts

endosymbiotic theory

The endosymbiotic theory provides a fascinating explanation for the origin of mitochondria in eukaryotic cells. According to this theory, mitochondria were once free-living prokaryotic organisms. These prokaryotes were engulfed by ancestral eukaryotic cells, leading to a symbiotic relationship. Over time, this relationship became so integrated that the engulfed prokaryotes evolved into the mitochondria we know today.
This theory is supported by multiple lines of evidence, making it a cornerstone in our understanding of cellular evolution.

mitochondrial DNA

A key piece of evidence for the prokaryotic origin of mitochondria is the presence of mitochondrial DNA (mtDNA). Unlike the linear DNA found in the nucleus of eukaryotic cells, mtDNA is circular, resembling the DNA of prokaryotes.
This similarity suggests that mitochondria inherited their genetic material from their prokaryotic ancestors. Moreover, mtDNA encodes some of the proteins required for mitochondrial function, further highlighting its prokaryotic origins.

prokaryotic ribosomes

Ribosomes within mitochondria share remarkable similarities with prokaryotic ribosomes. Both types of ribosomes are similar in size and shape, and they function in a comparable manner. This is in contrast to the larger, more complex ribosomes found in the cytoplasm of eukaryotic cells.
The resemblance between mitochondrial and prokaryotic ribosomes supports the idea that mitochondria have a prokaryotic origin, having retained some of the molecular machinery of their ancestors.

binary fission

The process of binary fission in mitochondria offers further evidence for their prokaryotic origin. Unlike eukaryotic cells, which typically divide through mitosis, mitochondria replicate by binary fission. This method of division is characteristic of prokaryotes.
During binary fission, the mitochondrial DNA is replicated, and the organelle splits into two, ensuring that each resulting mitochondrion has a complete set of genetic material.
This replication mechanism is a clear indication of the ancestral link between mitochondria and prokaryotic cells.

double membrane structure

Mitochondria are unique in eukaryotic cells due to their double membrane structure. This structural feature aligns with the endosymbiotic theory, which suggests that the inner membrane originated from the membrane of the engulfed prokaryote, while the outer membrane came from the host eukaryotic cell.
The presence of these two membranes is consistent with the theory that a prokaryotic cell was engulfed and retained within a eukaryotic host cell. This double membrane serves as a living fossil, providing a physical record of the mitochondrial origin story.