Biochemical controls: surviving deep sea pressure (Introduction)

by David Turell , Monday, September 09, 2024, 20:16 (9 days ago) @ David Turell

Specialized molecules:

https://www.quantamagazine.org/the-cellular-secret-to-resisting-the-pressure-of-the-dee...

"At the deepest point, the pressure of 36,200 feet of seawater is greater than the weight of
an elephant on every square inch of your body. Yet Earth’s deepest places are home to life
uniquely suited to these challenging conditions. Scientists have studied how the bodies of some large animals, such as anglerfish and blobfish, have adapted to withstand the pressure. But far less is known about how cells and molecules stand up to the squeezing, crushing weight of thousands of feet of seawater.

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"...the interdisciplinary team discovered that the membranes of comb jellies that reside in the depths are made of lipid molecules with completely different shapes than those of their shallow-water counterparts. Three-quarters of the lipids in the deep-sea comb jellies were plasmalogens, a type of curved lipid that is rarer in surface animals. In the pressure of the deep sea, the curvy molecule conforms to the exact shape needed to support a sturdy yet dynamic cell membrane.

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"Plasmalogen lipids are also found in the human brain, and their role in deep-sea membranes could help explain aspects of cell signaling. More immediately, the research unveils a new way that life has adapted to the most extreme conditions of the deep ocean.

"The cells of all life on Earth are encircled by fatty molecules known as lipids. If you put
some lipids in a test tube and add water, they automatically line themselves up back to back:
The lipids’ greasy, water-hating tails commingle to form an inner layer, and their water-loving heads arrange together to form the outer portions of a thin membrane. “It’s just like oil and water separating in a dish,” Winnikoff said. “It’s universal to lipids, and it’s what makes them work.”

"For a cell, an outer lipid membrane serves as a physical barrier that, like the external wall of a house, provides structure and keeps a cell’s insides in. But the barrier can’t be too solid: It’s studded with proteins, which need some wiggle room to carry out their various cellular jobs, such as ferrying molecules across the membrane. And sometimes a cell membrane
pinches off to release chemicals into the environment and then fuses back together again.

"For a membrane to be healthy and functional, it must therefore be sturdy, fluid and dynamic at the same time. “The membranes are balancing right on the edge of stability,” Winnikoff said. “Even though it has this really well-defined structure, all the individual molecules that make up the sheets on either side — they’re flowing around each other all the time. It’s actually a liquid crystal.”

"One of the emergent properties of this structure, he said, is that the middle of the membrane is highly sensitive to both temperature and pressure — much more so than other biological molecules such as proteins, DNA or RNA. If you cool down a lipid membrane, for example, the molecules move more slowly, “and then eventually they’ll just lock together,” Winnikoff said, as when you put olive oil in the fridge. “Biologically, that’s generally a bad thing.” Metabolic processes halt; the membrane can even crack and leak its contents.

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"The deep-sea comb jellies had membrane lipids that, at our standard atmospheric pressure, have a curvier shape than those in surface cell membranes. The animals had especially increased production of the group of lipids known as plasmalogens.

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"At the surface, a plasmalogen has a small phosphate head and a pair of wide, flaring tails, resembling a badminton shuttlecock, he said. But at high pressure, the tails squeeze
together to form the necessary sturdy yet dynamic structure. “They start their lipids at a different shape,” Budin said. “So when you compress them, they still maintain the right Goldilocks shape that you see in our own cells, but at these extreme pressures.” Budin and Winnikoff named this novel modification “homeocurvature adaptation.”

"Taking a plasmalogen membrane to the deep sea is like pushing down on a spring, Bartlett
said. At the surface, when the spring’s tension is released, it extends dramatically. “That’s
when you can imagine the cells, their membranes, falling apart.” Meanwhile, if a surface membrane with straighter lipids is brought down to the deep, it compresses too much and becomes too rigid to function properly."

Comment: the precise structure of plasmalogens to fit the requirements of deep sea high pressures is a strict example of the need for design.