THE BIOSYNTHESIS OF PROTEINS
There can be little doubt that the specific information necessary for the biosynthesis of proteins is, in some way, woven into the structure of the deoxyribonucleic acids of the chromosome. Ample support for this conclusion is given by the numerous observations that have related Mendelian genes to individual protein molecules. As we have seen, the most direct evidence has come from instances in which the genetic results could be compared with the chemical and physical properties of isolated, homogeneous proteins, such as hemoglobin, tyrosinase, and ß-lactoglobulin. Equally convincing are the results obtained by bacteriologists and virologists who have demonstrated that highly purified samples of DNA are capable of modifying both the genotype and phenotype of recipient cells, or of inducing the formation of the relatively complicated protein complex which characterizes the bacteriophage particle.
It is clear, however, that protein synthesis can take place outside the nucleus itself. In the reticulocyte, for example, hemoglobin synthesis proceeds at a rapid rate, and not until the cell has become a mature erythrocyte does such synthesis cease. Similarly, in the alga Acetabularia mediterranea, whose cell may be separated into nuclear