Biological complexity: more irreducible complexity (Introduction)

by David Turell , Tuesday, January 24, 2017, 01:08 (2643 days ago) @ David Turell

These large molecules are controls over function. They must appear in evolution at the same time the process they control is fully designed and put in place:

https://www.sciencedaily.com/releases/2017/01/170123151408.htm

"By determining the three-dimensional structures of these molecules down to the level of atoms, the researchers have unlocked key details as to how they function in the body.

"Using a state-of-the-art imaging technology in which molecules are deep frozen, scientists in Roderick MacKinnon's lab at Rockefeller University have reconstructed in unprecedented detail the three-dimensional architecture of three channels that provide a path for specific types of ions to travel across a cell's protective membrane. Because such ions are central to biochemical messaging that allows cells to communicate with one another, the findings have implications for understanding how muscles contract, how the heart maintains its rhythm, and many other physiological processes.

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"The chloride channel, known as CLC, opens to passively allow ions through. However, it has a close relative that moves chloride another way: by exchanging it for protons. In their structural data, Eunyong Park, a postdoc in the MacKinnon laboratory, and Ernest B. Campbell, a research specialist, found a detail that helps to explain how these two similar molecules work so differently: the position of a loop within the pore through which the ions travel. In the exchanger molecule, this loop was already known to partially block the ions' path. In the new CLC structure (above), they saw this loop flipped down, allowing chloride to travel more freely.

"By allowing potassium and sodium to travel through the cell's membrane, the HCN channel contributes to rhythmic electrical signals, including the pacemaker current within the heart. Among similar channels, HCN's contrarian responses to changes in voltage set it apart. While others open as the cell ramps up for a signal, HCN closes. And unlike the others, it opens as the cell returns to rest. Postdoc Chia-Hsueh Lee found features that contribute to this difference, including an extra-long arm within HCN's voltage detecting sensor (blue) as compared to that of a related potassium channel (orange). The longer arm likely stabilizes the pore in a closed position after the start of an electrical impulse.

"To prevent high frequency electrical impulses from running out of control, the channel Slo2.2 puts on the breaks by allowing potassium out of the cell. It does so in response to the sodium that rushes in during a signal. Richard Hite, a postdoc, and his colleagues had already determined what Slo2.2 looks like when it is closed, without sodium around. In new research, published January 19 in Cell, Hite exposed the channel to varying concentrations of its trigger ion, so as to determine the distribution of all the structures that occur simultaneously at a particular sodium concentration -- the first such experiment. It turned out that the channel exists only in two conformations, closed and open. As a result, it undergoes a sharp transition when opening, akin to a light switch being turned on."

Comment: the body uses ions, electrical impulse equivalents, to run various processes and organs like the heart. Think of this: the heart beats and this drives a circulatory pulse of blood. The beat is triggered by electric impulses traveling down biological 'wires' to drive the muscle contractions. Did evolution design a chambered heart and add the impulses later? Of course not. It had to be put all together completely at once. Saltation by God. Be sure to look at the diagrams in the article. Giant molecules. How did chance evolution found those molecules with the proper form for function?