News: Major insights into evolution of life reported by UCLA molecular biologist.

Major insights into evolution of life reported by UCLA molecular
biologist

http://www.sciencecentric.com/news/article.php?q=09081946-major-insights-into-evolution-life-reported-by-ucla-molecular-biologist

Humans might not be walking on the face of the Earth were it not for
the ancient fusing of two prokaryotes - tiny life forms that do not
have a cellular nucleus. Important new insights about prokaryotes and
the evolution of life are published by UCLA molecular biologist James
A. Lake 20 August in the advanced online edition of the journal
Nature.

Endosymbiosis refers to a cell living within another cell. If they
live together long enough, the two organisms will exchange genes; they
merge, but often keep their own cell membranes, and sometimes keep
their own genomes.

Lake has discovered the first exclusively prokaryote endosymbiosis.
All other endosymbioses have involved a eukaryote (a cell with a
nucleus, as found in all multicellular forms of life, such as humans,
animals and plants).

'This relationship resulted in a totally different type of life on
Earth,' said Lake, UCLA distinguished professor of molecular, cell and
developmental biology and human genetics. 'We thought eukaryotes
always needed to be present to do it, but we were wrong.'

'This work is a major advance in our understanding of how a group of
organisms came to be that learned to harness the sun and then effected
the greatest environmental change the Earth has ever seen, in this
case with beneficial results,' said Carl Pilcher, director of the NASA
Astrobiology Institute, headquartered at NASA Ames Research Centre in
Moffett Field, CA, which co-funded the study, along with the National
Science Foundation.

In the Nature paper, Lake is reporting that two groups of prokaryotes,
known as actinobacteria and clostridia, came together and produced the
'double membrane' prokaryotes.

'Higher life would not have happened without this event,' Lake said.
'These are very important organisms. At the time these two early
prokaryotes were evolving, there was no oxygen in the Earth's
atmosphere. Humans could not live. No oxygen-breathing organisms could
live.'

The oxygen on the Earth is the result of a sub-group of the double
membrane prokaryotes, Lake said. These organisms, the cyanobacteria,
have been growing tremendously, pumping oxygen into the atmosphere; we
could not breathe without them. In addition, the double membrane
prokaryotic fusion supplied the mitochondria that are present in every
human cell, he said.

'Along came these organisms - the double membrane prokaryotes - that
could use sunlight,' he said. 'They captured this vast energy
resource. They were so successful that they have more genetic
diversity in them than all other prokaryotes.

'We have a flow of genes from two different organisms (clostridia and
actinobacteria) together,' he said. 'Because the group into which they
are flowing has two membranes, we hypothesise that that was an
endosymbiosis that resulted in a double membrane. It looks as if a
single-membrane organism has engulfed another. The genomes are telling
us that the double membrane prokaryotes combine sets of genes from the
two different organisms.'

In this study, Lake has looked back more than two-and-a-half billion
years. He conducted an analysis of the genomics of the five groups of
prokaryotes.

Lake is interested in learning how every organism is related.

'We all are interested in our ancestors,' he said. 'A friend at UC
Berkeley, Alan Wilson, was the first person to collect DNA from large
numbers of people around the world. He showed that we are all related
to a woman who lived in Africa 200,000 years ago. Some in the media
called her Eve. He called her the Lucky Mother, the mother of us all.

'In our field, we have enormous amounts of data, but cannot make sense
of it all. Endosymbiosis allows us to start to understanding things;
it tells us that many genes are exchanged.

'We have been overlooking how important cooperation is. If two
prokaryotes get together, they can change the world. They
re-structured the atmosphere of the Earth. It's a message that
evolution is giving us: Cooperation is a way to get ahead.'

Actinobacteria have an unusual DNA composition, with a very high
amount of the 'G' and 'C' chemicals called nucleotides - whose
patterns carry the data required for constructing proteins.
(Nucleotides are designated by the letters A, G, C and T. The sequence
of nucleotides serves as a chemical code.) Some are pathogens,
including ones that cause tuberculosis and leprosy.

Some clostridia can photosynthesise, which no other single membrane
prokaryote does. Photosynthesis may have been developed in clostridia.

Double membrane prokaryotes include the pathogens that cause ulcers,
as well as the organisms that led to the creation of the chloroplasts
that are in all green plants, which make their growth possible.

--
Bob.

.

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