Endosymbiotic relationship theory

Endosymbiotic relationships - The Endosymbiotic Theory

endosymbiotic relationship theory

Symbiogenesis, or endosymbiotic theory, is an evolutionary theory of the origin of eukaryotic .. Genome comparisons suggest a close relationship between mitochondria and Rickettsial bacteria. Genome comparisons suggest a close. They began to live in what we call symbiotic relationships. The theory that explains how this could have happened is called endosymbiotic. The term symbiotic refers to two organisms living in a close association with one another, where both individuals benefit. The term endosymbiotic then refers to a.

In endosymbiotic theory, consistent with general evolutionary theory, all organisms arose from a single common ancestor.

Endosymbiotic Theory | Ask A Biologist

This ancestor probably resembled a bacteria, or prokaryote with a single strand of DNA surrounded by a plasma membrane. Throughout time, these bacteria diverged in form and function. Some bacteria acquired the ability to process energy from the environment in novel ways. Photosynthetic bacteria developed the pathways that enabled the production of sugar from sunlight. Other organisms developed novel ways to use this sugar is oxidative phosphorylationwhich produced ATP from the breakdown of sugar with oxygen.

ATP can then be used to supply energy to other reactions in the cell. Both of these novel pathways led to organisms that could reproduce at a higher rate than standard bacteria. Other species, not being able to photosynthesis sugars or break them down through oxidative phosphorylation, decreased in abundance until they developed a novel adaptation of their own.

The ability of endocytosis, or to capture other cells through the enfolding of the plasma membrane, is thought to have evolved around this time. These cells now had the ability to phagocytize, or eat, other cells.

In some cells, the bacteria that were ingested were not eaten, but utilized. By providing the bacteria with the right conditions, the cells could benefit from their excessive production of sugar and ATP. One cell living inside of another is called endosymbiosis if both organisms benefit, hence the name of the theory.

Endosymbiotic Theory

Endosymbiotic theory continues further, stating that genes can be transferred between the host and the symbiont throughout time. This gives rise to the final part of endosymbiotic theory, which explains the variable DNA and double membranes found in various organelles in eukaryotes.

While the majority of cell products start in the nucleus, the mitochondria and chloroplast make many of their own genetic products. The nucleus, chloroplasts, and mitochondria of cells all contain DNA of different types and are also surrounded by double membranes, while other organelles are surrounded by only one membrane. Endosymbiotic theory postulates that these membranes are the residual membranes from the ancestral bacterial endosymbiont.

If a bacteria was engulfed via endocytosis, it would be surrounded by two membranes. The theory states that these membranes survived evolutionary time because each organism retained the maintenance of its membrane, even while losing other genes entirely or transferring them to the nucleus.

Endosymbiotic theory is supported by a large body of evidence. The general process can be seen in the following graphic. Endosymbiotic Theory Evidence The most convincing evidence supporting endosymbiotic theory has been obtained relatively recently, with the invention of DNA sequencing.

DNA sequencing allows us to directly compare two molecules of DNA, and look at their exact sequences of amino acids. Logically, if two organism share a sequence of DNA exactly, it is more likely that the sequence was inherited through common descent than the sequence arose independently. If two unrelated organisms need to complete the same function, the enzyme they evolve does not have to look the same or be from the same DNA to fill the same role.

endosymbiotic relationship theory

Thus, it is much more likely that organisms who share sequences of DNA inherited them from an ancestor who found them useful. But to get from a prokaryote to a eukaryote, the cell needed to become a lot more complicated.

How we think complex cells evolved - Adam Jacobson

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? 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. All eukaryotic cells, like your own, are creatures that are made up of the parts of other creatures. Mitochondria, the important energy generators of our cells, evolved from free-living cells. They were prokaryotes that ended up inside of other cells host cells.

endosymbiotic relationship theory

They may have joined the other cell by being eaten a process called phagocytosisor perhaps they were parasites of that host cell. Rather than being digested by or killing the host cell, the inner cell survived and together they thrived.

The host cell provides a comfortable, safe place to live and the organelle pays rent by making energy that the host cell can use. This happened a long time ago, and over time the organelle and the host cell have evolved together.

Now one could not exist without the other. Today they function as a single organism, but we can still find evidence of the free-living past of the organelles if we look closely. What Evidence Supports Endosymbiotic Theory?

  • The Evolution of the Cell
  • Structural Biochemistry/The Endosymbiotic Theory

But in the field of science, a theory is a well established explanation based on extensive experimentation and observation. Scientific theories are developed and verified by the scientific community and are generally accepted as fact. And both organelles use their DNA to produce many proteins and enzymes required for their function. A double membrane surrounds both mitochondria and chloroplasts, further evidence that each was ingested by a primitive host.

The two organelles also reproduce like bacteria, replicating their own DNA and directing their own division. It is passed down directly from mother to child, and it accumulates changes much more slowly than other types of DNA. Because of its unique characteristics, mtDNA has provided important clues about evolutionary history. For example, differences in mtDNA are examined to estimate how closely related one species is to another.

Analysis of mitochondrial DNA from people around the world has revealed many clues about ancient human migration patterns. Models for Astrobiology Archaea survive today in extremely harsh environments, such as evaporative salt ponds on the edge of Great Salt Lake above and the boiling hot springs of Yellowstone National Park right.

Conditions on Earth 4 billion years ago were very different than they are today.