The Elements of Evolution (49-4) Cells

Cells

Cells are in many ways optimized for processing materials and interacting with the environment; so too many organisms in their construction and operation.

Through exquisite adaptation, microbes perfected metabolism to near the optimality afforded by physical chemistry, with the slight trade-off of being able to adjust to alternative nutritional conditions. This efficiency goes a long way in explaining the diversity, versatility, and staying power of the littlest life. In shedding all inessentials while wisely retaining contingency tools, viruses took economy to an extreme.

In a chemically chaotic environment, an E. coli bacterium feels its way to a food source using surface receptors fore and aft, relying upon a mental heuristic with a reliability in decision-making so fine that it couldn’t perform much better if it considered every single molecule in the neighborhood.

Optimality also abounds in eukaryotic cells. The ribosome, for instance, has maximal self-production efficiency, both in the number of proteins and their composition. Ideally, ribosomal proteins should be ~3 times smaller than an average cellular protein, and they should all be roughly similar in size – just as they are.

Because cells can make ribosomal RNA much faster than proteins, the more RNA that a ribosome has, the more rapidly a ribosome may be produced. Ribosomes are stuffed with as much RNA as possible to maximize the rate at which more ribosomes may be made.

Mitochondria – the power plants within cells – are about as efficient as they can be in producing energy. Inefficiencies are attributed solely to the limits of chemical reactions between the various elements employed.

The number of mitochondria within a cell are also optimized. The more mitochondria, the greater the rate of ATP production, and thereby the faster the response to meet physiological needs. But there are energy and material costs to having excess mitochondria, so their production is tightly regulated.

The nucleus manages 99.75% of the DNA found within a eukaryotic cell. The mitochondria have the other 0.25%. In evolutionary time, mitochondria kept most of the DNA needed for their operation, while relinquishing the inessential to the nucleus. This is a most efficient distribution, as are the management practices of these organelles in employing their DNA.

The mitochondria organelle contains a small chromosome with only 37 genes, but these genes are absolutely essential for metabolism. In order for ATP to be produced properly in a cell, a few hundred other genes encoded in the nucleus must interact directly with the 37 mitochondrial genes. ~ American evolutionary geneticist Felipe Barreto