Biological complexity: finding Nucleolus functions (Introduction)

by David Turell , Friday, May 20, 2016, 22:21 (2892 days ago) @ David Turell

This little dark spot in all nuclei has definite functions in the handling of RNA's, while being composed of liquid layers:-http://phys.org/news/2016-05-liquid-fluid-self-organizes-cell-growth.html-"Although known since the 1830s as a round, dark spot in a cell's nucleus, only recently has the nucleolus gotten its full due. Scientists have learned that besides building a cell's protein factories, this specialized subunit, or organelle, serves more broadly as a control center for cellular growth and health. - ***-"somehow, this biological droplet maintains a complex, compartmentalized internal structure. Brangwynne, an assistant professor of chemical and biological engineering, and other researchers have puzzled over how such a liquid-like object could develop stably compartmentalized layers, rather than just fusing into a homogenous glob.-***-"the constituent proteins and RNA of nucleoli spontaneously assemble themselves into three distinct, liquid layers, thanks to their differing properties such as surface tension and viscosity. Rather like how oil and water can coexist yet remain separate, the nucleolus develops liquid subcompartments, which enable its critical functions. -***-"the protein-based lab work, led by Vaidya, found that droplets of the two main nucleolar proteins, dubbed FIB1 and NPM1, would not blend into each other as a homogenous fluid. Instead, because FIB1's surface tension was higher than NPM1, the former became engulfed by the latter, precisely mimicking the nucleolar structure seen in living cells. As a demonstration of this phenomenon, the researchers also created similar multi-phase drops —liquids embedded within other liquids—using vegetable oil and silicone oil in water.- ***-"For the nucleolus, this layered form follows function. Newly made RNA molecules proceed from the organelle's core into the middle, then outer components, receiving modifications as they do so, as if on an assembly line. Like a factory, nucleoli churn out these RNA bits, which after leaving the nucleolus ultimately enter into the cell's cytoplasm and link up to form structures called ribosomes. Factories in their own right, these ribosomes manufacture a cell's many thousands of proteins.-"Beyond making ribosomes, the nucleolus has lately emerged as a hub for coordinating cellular growth, helping to regulate cell division and even setting the timing of a cell's self-destruction in reaction to stress or damage."-Comment: How much complexity has to be shown in the cell before it is realized that this structure as well as the rest of the cell must have been planned from the beginning? All of this apparatus runs at high speed second by second, and is monitored for mistakes by feedback loops. How did evolution in a blind search find these two cooperative liquids with differing surface tensions? Check out my entry: Friday, May 20, 2016, 15:04 to see Kaufmann's thoughts.