Biological complexity: cell cytoplasm can self-organize (Introduction)

by David Turell , Thursday, January 02, 2020, 18:39 (1574 days ago) @ David Turell

It is built into protein molecules to organize and position themselves:

https://www.quantamagazine.org/unscrambled-eggs-self-organization-restores-cells-order-...

"If simply left alone, the liquid innards of a cell — its cytoplasm — have a surprising capacity to reassemble, even without components that appeared essential to some scientists. Experiments recently described in Science revealed the unanticipated extent of this talent and delved into its mechanics. They vividly illustrated how well equipped cells are to restore themselves to order after chaos intrudes,

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"Self-organization occurs at many levels in living systems. String the right sequence of amino acids together and a long peptide chain will fold itself into a working protein. Cells within an early embryo arrange themselves to generate tissues to build a human.

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"Cheng and Ferrell are the first to get the entire cytoplasm to arrange itself as if inside a whole cell, said Rebecca Heald, a cell biologist at the University of California, Berkeley.
“It’s an amazing demonstration of the properties of the cytoplasm and its ability to self-organize,” she said. “Visually, it’s incredibly striking that you can have this kind of organization happen spontaneously after homogenizing these eggs.”

"Seeing the compartments emerge made Cheng and Ferrell want to know how it happened...However, they quickly zeroed in on another suspect: a star-shaped organelle called an aster derived from the sperm.

"Seeing the compartments emerge made Cheng and Ferrell want to know how it happened. They knew at the outset that the DNA contained in the sperm was not responsible, since self-organization wouldn’t require the expression of genes. However, they quickly zeroed in on another suspect: a star-shaped organelle called an aster derived from the sperm.

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"These asters, constructed of hollow rods called microtubules, sprout from a structure known as the centrosome, which organizes the microtubules. When cells rest between divisions, microtubule asters organize the cell’s contents. Frog eggs lack usable centrosomes, so when Cheng added the sperm, he gave the cytoplasm a powerful organizational tool.

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“'That doesn’t surprise me, but I am sure it surprised other people,” Heald said. Her own research, along with that of others, has shown that it’s possible to create microtubule structures without centrosomes. The key lies with microtubules themselves. “Biology is full of redundancy, because when a process is very important, you want to have multiple mechanisms supporting it,” she said. (my bold)

"Like magnets, microtubules are polarized. With their plus ends growing outward and minus ends attached to the centrosome, which is often near the nucleus, they form what Heald describes as a compass within the cell. Motor proteins, such as dynein, ferry cargo along the microtubules, guided by their polarity.

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"The self-organized compartments lack one major component of cells: membranes. The membrane surrounding a cell defines it and its relationship with the outside world.

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"Like the nuclei within the developing fruit fly embryo, the compartments that contained sperm in Cheng and Farrell’s experiments divided to produce more of themselves — a “completely unexpected” result to Heald. Normally, membranes would delineate this process, but instead voids surrounding the compartments became the boundaries. “Unless you have a boundary, you can’t see a division happening,” she said. “This spontaneously made a boundary.'”

Comment: The key issue is to understand that proteins do all of this as if they come with a programmed agenda. Well perhaps they do and were designed to act this way from the beginning of organic chemistry as it appeared on Earth. God the designer fits better than assuming nature did it by chance.