Biological complexity: multiple cell machine (Introduction)

by David Turell , Thursday, February 23, 2017, 02:09 (2831 days ago) @ David Turell

Our cells are constantly at work producing new product, getting rid of old stuff. this article is a review of a number of new discoveries of complexity:

http://www.evolutionnews.org/2017/02/more_marvels_in103504.html

"Here's another new paper about voltage-gated sodium channels, called Navs. In humans, these are involved in sensory neurons as well as heart and brain cells, but even microbes have them.

"The cycling of Navs through open, closed and inactivated states, and their closely choreographed relationships with the activities of other ion channels lead to exquisite control of intracellular ion concentrations in both prokaryotes and eukaryotes.

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"the machines that repair double-stranded breaks in DNA are "far more complex than previously assumed." For instance, "The ends of breaks in the double helix are not just joined, they are first changed in a meticulously choreographed process so that the original genetic information can be restored."

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"'Protein chaperone takes its job seriously." What is it? It's a ribosomal protein's secret service bodyguard, essentially:

"For proteins, this would be the equivalent of the red-carpet treatment: each protein belonging to the complex machinery of ribosomes -- components of the cell that produce proteins -- has its own chaperone to guide it to the right place at the right time and protect it from harm.

"The particular protein they studied, named L4, has a chaperone that fits tightly like a hand and glove. When the protein is produced in the nucleus, the chaperone takes it on a long trip out the nuclear pore and into the cytoplasm, where it has to be fitted into the ribosome at the right place and time.

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"Building ribosomes is a formidable undertaking for the cell, involving about 80 proteins that make up the ribosome itself, strings of ribosomal RNA, and more than 200 additional proteins that guide and regulate the process. "Ribosome assembly is a dynamic process, where everything happens in a certain order. We are only now beginning to elucidate the many steps involved," says [André] Hoelz.

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"One more little factoid if you're not impressed yet: "More than a million ribosomes are produced per day in an animal cell."

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"the 26S Proteosome, "a large multisubunit complex that executes the degradation of intracellular proteins marked for destruction," contains an "engine" with moving parts. This engine "unfolds and translocates substrates into the 20S core particle" where the protein is shredded, allowing its amino acids to be recycled. How does the machine know what to recycle?...Here, we report cryo-EM structures of the yeast 26S proteasome in the presence of different nucleotides and nucleotide analogs, revealing the existence of four distinct conformational states. These structures elucidate the conformational changes underlying substrate translocation and their coupling with gate opening.

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"'The ability to dispose of proteins that are either aberrant or (in the worst case) toxic is fundamental to a cell's survival, Researchers describe "rescue proteins" that patrol ribosomes, providing the necessary quality control on the assembly line. The next question is: how do they recognize errors?

"Using cryo-electron microscopy to study the structure of such ribosome-mRNA complexes, the researchers were able to show the manner in which special rescue proteins (Dom34 and Hbs1) recognize such stalled ribosomes, thereby initiating the splitting of the arrested complex and the degradation of the faulty mRNA. The rescue proteins recognize arrested ribosomes by detecting, and binding to, conserved locations normally occupied by mRNA. This direct competition-based approach ensures that only ribosomes with aberrant mRNAs are targeted.

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"an article describes protein machines that attach to mRNAs as they exit the nucleus and stabilizes them for transport. "We were surprised to see that the RNA is not only recognized by these proteins, they also force it to adopt a new form. They staple it together, so to speak." Then the motor proteins "take the mRNA train," carrying the passenger down the cell's "railway lines," the article says picturesquely.

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"When cells get too sparse, they pull on each other, triggering cell division and the creation of new cells to fill in the gaps. But then, they discovered a protein machine responsible for this balance. It's called Piezo1, named undoubtedly for its mechanosensitive nature, like certain crystals that can spark when compressed. Piezo1 acts like a "thermostat" on both sides of the cell, they found.

"Just like a thermostat regulates both heat and cold, it makes sense to have one sensor measuring crowding and stretch. If there were two separate regulators, things could get out of hand fairly quickly if one sensor breaks."

Comment: Read the article. I can't put in more. Only design can plan this.