The conversation is a bit confusing but maybe this will help a bit (1) optimizing *efficiency* of energy production is not the single most important factor driving evolution of single cell organisms or functionality of cells in complex organisms. Efficiency requires complexity and additional energy expenditure. Sometimes all you need is a certain level of efficiency. If all you do is multiply in a reasonably nutrient rich environment, why bother with unneeded genetic complexity? (2) mitochondria vary from organism to organism and tissue to tissue. They evolved to adapt to their cell environment over hundreds of millions of years. Some are more efficient than others. ATP production may not always be their prime or most demanding function under certain circumstances. Stem cells are glycolytic. Adipose tissue during hibernation are uncoupled. Etc. Aerobic bacteria do just fine in their environments. Protoeukaryotic host of protomitochondria was probably more concerned with detoxifying O2 than having more ATP. That was a bonus

I mean mitochondria is a more powerful bio-engine to generate ATP. Then why bacteria did not adapted to have organelles such as mitochondria and others during the time course of evolution? Can any body some web link to find out which bacteria have mitochondrial ETC?

Hey Paital,

It is hypothesized that present-day organelles such as mitochondria and chloroplasts were once independent cells that gradually evolved to get integrated into eukaryotic cells. This theory is called Endosymbiotic theory.

http://en.wikipedia.org/wiki/Endosymbiotic_theory

There are many observations that strongly support this theory, such as:

(1) Many mitochondrial proteins are encoded by the nucleus

(2) Strong homology of mitochondrial genes to some of those of bacterial origin

So, the answer to your question is as follows. "The proteobacteria itself evolved to be the present-day mitochondria, atleast according to the endosymbiotic theory".

Hope I answered your question. For more details on the origin of mitochondria, check this review. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC138944/

Best,

Sagar S

Thanks Mr sagar

Hi Dr. Patial bacterias do have equivalent of ETC on their plasma membrane. The mitochondrial inhibitors and uncouplers act as general non-specific antimicrobials.

http://www.microbelibrary.org/library/biology/2678-bacterial-respirationelectron-transport-and-bacterial-chemiosmotic-phosphorylation

They do not have the need to make it membrane-bound as they are serving their purpose.

Mr Datta thanks for your answer. Both eukaryotes and prokaryotes have ETC but only in eukaryotes chemiosmotic gradient is maintained due to the presence of mitochondria. For this reason, ETC and oxidative phosphorylation in eukaryotes is more efficient than the bacterial ETC. That means having mitochondria is an advantage in eukaryotes for transport of electrons and ATP production. Due to such relationships or similarity between mitochondria and bacteria, endosymbiotic type of theory have been proposed with evidence. The point is mitochondrial ETC is more powerful than the bacterial plasma membrane ETC. One the other hand only solving the purpose is not the only criteria of evolution rather easier way of solving problems is the more preferable criteria for evolution. So, if mitochondria are powerful organelle having more efficiency than bacterial ETC in general, why bacteria are evolved to mitochondria rather than bacteria could evolved/adapt to have their own membrane bound and powerful ETC system such as mitochondria? If that would have done then they might become more powerful with a good energetic machine. If evolution was not limited to bacteria, then why bacteria did not evolve to have their own mitochondria?

I think answers such as "bacteria have their own ETC to solve the problem therefore they did not tend to adapt mitochondria in their cellular compartment, or bacteria are evolved to mitochondria" etc. are not the exact reply to my question.

The conversation is a bit confusing but maybe this will help a bit (1) optimizing *efficiency* of energy production is not the single most important factor driving evolution of single cell organisms or functionality of cells in complex organisms. Efficiency requires complexity and additional energy expenditure. Sometimes all you need is a certain level of efficiency. If all you do is multiply in a reasonably nutrient rich environment, why bother with unneeded genetic complexity? (2) mitochondria vary from organism to organism and tissue to tissue. They evolved to adapt to their cell environment over hundreds of millions of years. Some are more efficient than others. ATP production may not always be their prime or most demanding function under certain circumstances. Stem cells are glycolytic. Adipose tissue during hibernation are uncoupled. Etc. Aerobic bacteria do just fine in their environments. Protoeukaryotic host of protomitochondria was probably more concerned with detoxifying O2 than having more ATP. That was a bonus

Dear Prof. Mannella, your opinion is however highly appreciable in relation to my question. Thanks. If we talk about the evolution or modification of a particular biochemical pathway, then a certain gradual biochemical evolution has been noticed in animal kingdom also. I think you are saying that if a problem is solved by a simple process then why to acquire a complex system although it is with more efficiency?

In a word, yes.