The key difference between autogenous theory and endosymbiotic theory is that autogenous theory states that nucleus and cytoplasm form through evolutionary changes in a single prokaryotic lineage while endosymbiotic theory states that some organelles, especially mitochondria and chloroplasts in eukaryotic cells, were once prokaryotic microbes living in a symbiotic relationship.
Eukaryotic cells are notably different from prokaryotic cells, and they have unique features. Most importantly, eukaryotic cells have a nucleus and important membrane-bound organelles. There are several theories explaining the evolution of eukaryotic cells and the origin of mitochondria and chloroplasts within the eukaryotic cells. Autogenous theory and endosymbiotic theory are two such theories. Autogenous theory describes the origin of the nucleus and cytoplasm inside the eukaryotic cells, while endosymbiotic theory describes the origin of mitochondria and chloroplasts within the eukaryotic cells.
CONTENTS
1. Overview and Key Difference
2. What is Autogenous Theory
3. What is Endosymbiotic Theory
4. Similarities Between Autogenous Theory and Endosymbiotic Theory
5. Side by Side Comparison – Autogenous Theory vs Endosymbiotic Theory in Tabular Form
6. Summary
What is Autogenous Theory?
Autogenous theory is one of the major theories on the formation of eukaryotic cells. According to this theory, the eukaryotic cell evolved directly from a single prokaryotic ancestor through compartmentalization of functions arising from invaginations of the prokaryotic plasma membrane. This theory states that the nucleus, cytoplasm and other organelles such as Golgi apparatus, vacuoles, lysosomes and the endoplasmic reticulum formed through evolutionary changes in a single prokaryotic lineage. Unlike endosymbiotic theory, which is only applied for mitochondria and chloroplasts, autogenous theory is accepted for the endoplasmic reticulum, Golgi, the nuclear membrane, and organelles enclosed by a single membrane such as lysosomes, etc.
What is Endosymbiotic Theory?
Endosymbiotic theory or endosymbiosis is a hypothesized process that explains the origin of some organelles in eukaryotic cells. This theory describes the mechanism by which mitochondria and chloroplasts entered eukaryotic cells. These two organelles have their own DNA. Therefore, scientists believe that mitochondria have originated in eukaryotic cells from autotrophic alphaproteobacteria via endosymbiosis. This is a result of a symbiotic relationship between a primitive eukaryotic cell and an autotrophic bacterium. This autotrophic bacterium was eaten by a primitive eukaryotic cell through phagocytosis. Once engulfed, the host cell had provided a comfortable, safe place to survive. Eventually, their symbiotic relationship had lead to the origin of mitochondria in eukaryotic cells.
According to this theory, chloroplasts have originated in plant cells from cyanobacteria through endosymbiosis. A cyanobacterium was eaten by a primitive eukaryotic cell with mitochondria. This had lead to the origin of chloroplasts inside the photosynthetic eukaryotic cells. Hence, the endosymbiotic theory scientifically explains how mitochondria and chloroplasts originated inside the eukaryotic cells from prokaryotic microbes.
Figure 01: Endosymbiotic Theory
Endosymbiotic theory was supported by several facts, including the sizes of mitochondria and chloroplasts. These two organelles are the same size as the prokaryotic cell. They are divided by binary fission similar to bacterial cells. Moreover, mitochondria and chloroplast have own DNA which is circular and have genes which are very similar to the genes of modern-day prokaryotes. Furthermore, mitochondria and chloroplast have ribosomes composed of 30S and 50S subunits similar to prokaryotic cells. These facts prove that these organelles are more closely related to prokaryotes. Thus, according to the endosymbiotic theory, these organelles in eukaryotic cells were once prokaryotic cells.
What are the Similarities Between Autogenous Theory and Endosymbiotic Theory?
- Autogenous theory and endosymbiotic theory are two theories that explain the origin of eukaryotic cells.
- Both theories believe that organelles in eukaryotic cells originated from prokaryotic cells.
What is the Difference Between Autogenous Theory and Endosymbiotic Theory?
Autogenous theory states that eukaryotic cells evolved directly from a single prokaryotic ancestor by compartmentalization of functions brought about by infoldings of the prokaryote plasma membrane while endosymbiotic theory states that certain organelles of eukaryotic cells evolved as a result of symbiotic associations with prokaryotic ancestors. Thus, this is the key difference between autogenous theory and endosymbiotic theory.
Moreover, the autogenous theory is accepted for the endoplasmic reticulum, Golgi, and the nuclear membrane, and of organelles enclosed by a single membrane while the endosymbiotic theory is only accepted for mitochondria and chloroplasts.
Below infographic tabulates the differences between autogenous theory and endosymbiotic theory.
Summary – Autogenous Theory vs Endosymbiotic Theory
Autogenous theory and endosymbiotic theory are two major theories on the formation of eukaryotic cells. The autogenous theory says that organelles such as the nucleus, Golgi apparatus, vacuoles, lysosomes and the endoplasmic reticulum arose directly from a single prokaryote ancestor through compartmentalization of functions arising from invaginations of the prokaryotic plasma membrane. The endosymbiotic theory on the other hand, says that certain eukaryotic organelles, especially mitochondria and chloroplasts, have evolved from prokaryotic organisms due to symbiotic relationships between them. According to that theory, those organelles were once prokaryotic cells living inside the eukaryotic cells. Thus, this summarizes the difference between autogenous theory and endosymbiotic theory.
Reference:
1. Martin, William F., et al. “Endosymbiotic Theories for Eukaryote Origin.” Philosophical Transactions of the Royal Society B: Biological Sciences, 26 Sept. 2015, royalsocietypublishing.org/doi/10.1098/rstb.2014.0330.
2. Staveley, Brian E. “Principles of Cell Biology (BIOL2060).” BIOL2060: Cell Biology, Memorial University of Newfoundland, Available here.
Image Courtesy:
1. “Serial endosymbiosis” By Kelvinsong – Own work (CC BY-SA 3.0) via Commons Wikimedia