Endosymbiosis | avesisland.info
The endosymbiotic theory is the accepted mechanism for how eukaryotic cells evolved from prokaryotic cells. First published by Lynn Margulis. Biologists and ecologists define a symbiotic relationship as an intimate interaction between two or more species, which may or may not be. Symbiogenesis, or endosymbiotic theory, is an evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms, first articulated in and
The mitochondria are suspended in the jelly-like cytosol of the cell.
- Mitochondria and chloroplasts
They are oval-shaped and have two membranes: Electron micrograph of a mitochondrion, showing matrix, cristae, outer membrane, and inner membrane. Modification of work by Matthew Britton; scale-bar data from Matt Russell. The matrix contains mitochondrial DNA and ribosomes. We'll talk shortly about why mitochondria and chloroplasts have their own DNA and ribosomes.
The multi-compartment structure of the mitochondrion may seem complicated to us. That's true, but it turns out to be very useful for cellular respirationallowing reactions to be kept separate and different concentrations of molecules to be maintained in different "rooms. Electrons from fuel molecules, such as the sugar glucose, are stripped off in reactions that take place in the cytosol and in the mitochondrial matrix.
These electrons are captured by special molecules called electron carriers and deposited into the electron transport chaina series of proteins embedded in the inner mitochondrial membrane. As protons flow back down their gradient and into the matrix, they pass through an enzyme called ATP synthase, which harnesses the flow of protons to generate ATP. This process of generating ATP using the proton gradient generated by the electron transport chain is called oxidative phosphorylation.
The compartmentalization of the mitochondrion into matrix and intermembrane space is essential for oxidative phosphorylation, as it allows a proton gradient to be established. These electrons are captured by special molecules called electron carriers and deposited into the electron transport, a series of proteins embedded in the inner mitochondrial membrane.
For instance, muscle cells typically have high energy needs and large numbers of mitochondria, while red blood cells, which are highly specialized for oxygen transport, have no mitochondria at all. Both mitochondria and chloroplasts contain their own DNA and ribosomes. Strong evidence points to endosymbiosis as the answer to the puzzle.
Symbiosis is a relationship in which organisms from two separate species live in a close, dependent relationship. The first endosymbiotic event occurred: The ancestral eukaryote consumed aerobic bacteria that evolved into mitochondria.
In a second endosymbiotic event, the early eukaryote consumed photosynthetic bacteria that evolved into chloroplasts. Bacteria also have DNA and ribosomes similar to those of mitochondria and chloroplasts. Even though there are many millions of life forms on earth, all of them are made up of only two basic types of cell: Prokaryotes pro-carry-oats are small and simple and have rings of circular DNA floating free inside the cell.
Eukaryotes you-carry-oats are large and more complex. They have a nucleus, which holds strings of linear DNA within a lipid membrane. All the life forms that you are used to seeing — animals including humansplants, and fungi — are made up of eukaryotic cells. The bacteria, which are too small to see without a microscope, are made up of prokaryotic cells.
Prokaryotic cells were some of the earliest life forms on earth. They first appear in the fossil record around 4 billion years ago. Prokaryotes were around for a long, long time before eukaryotic cells appeared around 1. This has led us to think that the ancestor of all eukaryotic cells was a prokaryote. But to get from a prokaryote to a eukaryote, the cell needed to become a lot more complicated.
Eukaryotic cells are powered by special organelles, which work a bit like batteries. All eukaryotes have an organelle called the mitochondrion, which makes energy to power the cell.
Plant cells have another type of organelle called a plastid. Plastids can harvest energy from sunlight, like a solar battery. Chloroplasts are a type of plastid.
What is Endosymbiotic Theory? How did the eukaryotes become so complicated?
Mitochondria and chloroplasts (article) | Khan Academy
And where did these battery-like organelles come from? We think we know part of the answer. Eukaryotic cells may have evolved when multiple cells joined together into one.
They began to live in what we call symbiotic relationships.
The theory that explains how this could have happened is called endosymbiotic theory. An endosymbiont is one organism that lives inside of another one. The cells of cockroaches contain bacteria, and cockroaches exhibit slowed development if the bacteria are killed with antibiotics.
The growth of the cockroach can be restored, however, with certain additions to its diet that the bacteria presumably were providing. The transmission of these bacteria from one cockroach to an offspring is hereditary, although not genetically based, because the bacteria invade the cytoplasm of the egg.
Then, when the egg is fertilized and develops, it already has the endosymbiont that the mother had. Another example of maternal transmission can be found in ruminating animals. In these animals, the mother passes the rumen microorganisms to her baby after it is born through her saliva and ruminated food, which contain all the microbial species the baby will need in life. If a baby ruminating animal is not allowed to be in contact with its mother, the baby may never get the microbes necessary for it to be able to digest plant material and will die.
Endosymbiotic Evolution From behaviors such as the migration of jellyfish to different water layers, and special structures such as the rumen of the stomach, it is clear that endosymbiosis involves complex interactions and that these organisms have evolved together for many generations in order to develop such interactions. Perhaps the oldest and most widespread example of this endosymbiotic co-evolution is in the origin of eukaryotic cells.
They evolved from prokaryotic cells, with the primary differences being that eukaryotic cells are larger and more complex, containing a separate nucleus and numerous organelles such as mitochondriawhereas prokaryotic cells are smaller with a few organelles floating freely in the cellular fluid.
Examples of prokaryotes are simple unicellular organisms such as bacteria. Most multicellular complex organisms, however, from protozoans to fungus to animals, are eukaryotes. How did eukaryotic cells arise? Athough there is no direct evidence, the most plausible theory is that an early prokaryotic cell, the ancestor to the mitochondrion, entered another prokaryotic cell, either as a food item or a parasite.
Over time, the relationship between the two became endosymbiotic, with the mitochondrion supplying energy to the host associate and the host providing the proper environment and nutrients to the mitochondrion. Thus, a cell with a distinct organelle, or a eukaryotic cell, emerged. This means that every single cell in all prokaryotic organisms has endosymbiotic organelles. Several characteristics of mitochondria support this widely accepted theory of an endosymbiotic evolution giving rise to eukaryotic cells: The mutually beneficial relationship between the cell, which provides nutrients and an environment for the organelle, and the mitochondrion, which provides energy for the cell, is seen in many other endosymbiotic systems, including those mentioned above.
The modern role of the mitochondrion is to provide energy in a usable form for the cell. The mitochondrion has a genome within it that lets it reproduce itself and be largely independent from the cell and the cell's genome, which resides in the nucleus. Finally, the mitochondrion does not divide and reproduce in the same manner as the host cell.
In sexually reproducing animals, for example, the mitochondria of the off-spring are not a mix of both parents' mitochondria.
Instead, they are all inherited from the mother.