Basic Biology - Molecules of life - Proteins

Weight comparisons

If we estimate the average weight of a human cell as about 10^-9 g, and remember that proteins constitute about one fifth of cell mass, then assuming the weight of an average protein to be about 10^-19 g, we see that there are 0.2 x 10^-9 / 10^-19 proteins per cell, which equals two billion (2 x 10⁹ ).

These of course are very rough estimates which would vary from cell to cell. If we remember that there are about 6 x 10¹³ cells, we see that there are 30,000 times more cells per human, than proteins per cell. This may be an indication of the relative complexity of a human compared to a single cellular organism. A similar estimate regarding the relative complexity of an elephant or dinosaur and human may not be flattering for a human.

Although forces such as hydrogen bonds are weak individually, when two or more biological macromolecules with complementary shapes come close to each other, the sum of all such weak forces may cause the molecules interact rather strongly, e.g. to make them stick together. In fact, such weak inter-molecular forces and interactions play a fundamental role in life and are at the basis of virtually all biological processes. For instance many proteins can stick together to form large protein complexes such as yeast RNA polymerase II, which reads and transcribes the genetic information. This protein has 10 subunits in it's structure.