Bacterial motors and other organelles (Introduction)

by David Turell , Friday, June 28, 2019, 21:11 (1757 days ago) @ David Turell

Bacteria are highly complex with specific organelles. Although without a specific nucleus they have specific functional areas:

https://www.quantamagazine.org/bacterial-organelles-revise-ideas-about-which-came-first...

"for the past few decades, researchers have been quietly uncovering many complex structures within prokaryotes, including membrane-bound organelles. In contrast to eukaryotes, which all have a suite of organelles in common, different groups of prokaryotes showcase their own specialized compartments.

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"And that list is only growing as scientists discover more and more compartments within supposedly simple bacterial cells. “Bacteria are a lot more complex, in other words, and may have a lot more similarities in their biology to eukaryotes than people have assumed in the past,” said John Fuerst, a microbiologist at the University of Queensland in Australia. The very existence of organelles in these bacteria, coupled with intriguing parallels to the more familiar ones that characterize eukaryotes, has prompted scientists to revise how they think about the evolution of cellular complexity — all while offering new ways to probe the basic principles that underlie it.

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“'Historically, people have known about compartments in bacterial cells that carry out specific functions for a long, long time, going back to the 1800s,” said Arash Komeili, a microbiologist at the University of California, Berkeley. Yet, while eukaryotic organelles have been studied in great detail for many decades, it has only recently become possible to do so in prokaryotes. Bacteria are tiny: orders of magnitude smaller than typical eukaryotic cells, and sometimes even smaller than eukaryotes’ organelles. That made it extremely difficult to isolate and analyze bacterial compartments to get a sense of what they were — and what they were doing.

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"A couple of decades ago, two-dimensional imaging by Fuerst and others seemed to indicate that the DNA of the bacterium Gemmata obscuriglobus was surrounded by a membrane, instantly raising comparisons to the eukaryotic nucleus. Those results have been called into question — imaging seems to indicate that the compartment isn’t entirely closed, meaning it does not satisfy the definition of an organelle — but experts remain excited about these bacteria. They have the most complex internal membrane system seen in prokaryotes to date, and they contain proteins that structurally resemble those that shape and maintain eukaryotic membranes. They also seem capable of processes that were thought to be unique to eukaryotes, such as digesting nutrients inside their cells and synthesizing molecules called sterols.

“'The problem is, we basically don’t know anything about [this membrane system],” said Damien Devos,

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"Bacteria also seem to have a wide variety of enclosed structures that are bound not by a lipid membrane but by a protein coat. Take carboxysomes, which evolved in bacteria twice, independently, to fix carbon. They and smaller, self-assembling nanocompartments have a polyhedral structure that looks shockingly like a viral capsid, the protein shell that encloses viral genomic material.

"The catalog keeps getting longer: Komeili and his colleagues recently discovered a new lipid-bound organelle that accumulates iron, which they’ve dubbed the ferrosome. Bacteria seem to have a cornucopia of such organelles, with more waiting to be discovered."

Comment: These studies raise the issue of just how complex was original life if it started with so-called simple bacteria. Perhaps not so simple and required a designer.