Biological complexity: cell life/death hangs by a thread (Introduction)

by David Turell , Saturday, June 24, 2017, 02:36 (2710 days ago) @ David Turell

An iron sulfur bond must be maintained by some energy or the cell can die:

https://www.sciencedaily.com/releases/2017/06/170622182832.htm

"Slight changes in the machinery of a cell determine whether it lives or begins a natural process known as programmed cell death. In many forms of life -- from bacteria to humans -- a single chemical bond in a protein called cytochrome c can make this call. As long as the bond is intact, the protein transfers electrons needed to produce energy through respiration. When the bond breaks, the protein switches gear and triggers the breakdown of mitochondria, the structures that power the cell's activities.

"For the first time, scientists have measured exactly how much energy cytochrome c puts into maintaining that bond in a state where it's strong enough to endure, but easy enough to break when the cell's life span is ending.

***

"The study marks the first time that anyone has been able to experimentally quantify how the rigid structure of the cytochrome c molecule supports this crucial bond between iron and sulfur atoms in what's known as an entatic state, where the protein maintains a bond that is just strong enough to perform both of its jobs.

"'This was important because we had shown the bond is weak and shouldn't be present at room temperature in the absence of the protein constraints," says Solomon. "But the protein is able to contribute energy to keep this bond intact for electron transfer. In this LCLS experiment, we determined exactly how much energy the rest of the protein contributes to maintaining the bond: about 4 kcal/mol that is derived from an adjacent hydrogen bond network."

"'We were able to show how nature tunes this system to change the properties on a fundamental level and perform two very different functions," Mara says. "The energy contribution by cytochrome c is really at a sweet spot. (my bold)
***

"Scientists knew from earlier studies that a particular iron-sulfur bond is key. When iron in the protein binds to sulfur contained in one of the protein's amino-acid building blocks, cytochrome c participates in electron transfer. By transferring electrons, the protein helps generate energy needed for biological processes that maintain life.

"But when cytochrome c encounters cardiolipin, a lipid present in the membrane of the cell's mitochondria, the iron-sulfur bond breaks, and the protein becomes an enzyme that creates holes in the mitochondria's outer membrane - the first step in programmed cell death.
These changes occur incredibly fast, in less than 20 picoseconds, so the experiment required ultrafast pulses of X-rays generated by LCLS to take snapshots of the process.

***

"Knowledge of cytochrome c's function is also valuable to the fields of bioenergy and environmental science, since it is a critically important protein in bacteria and plants.

Comment: this is a very precise balance. See my bold above. It is a mechanism in all branches of life. This cannot be the result of chance. Cell processes are designed and directed for them to work. Not by chance!