4 SOCIAL SCIENTIST
In short the solution of this age-old problem on the solid basis of experimental findings and of hypotheses tested at least partially in experiments has been placed firmly on the scientific agenda of the second half of the twentieth century.
The Basic Chemistry
Every organism is made up of proteins, nucleic acids, carbohydrates, fats and fat-like substances known as lipids, and mineral salts. The basic constituents have been identified as proteins and nucleic acids.
The protein molecule is made up of a string of twenty different amino acids. Of them two, aspartic and glutamic acids, arc acidic, and another two, lysine and organine, are basic. The remaining sixteen are neutral. These molecules form chains by means of peptide linkages. Two amino acids combine by a condensation reaction to form a dipeptide. Two dipcptides combine to form a tetrapeptidc and in this manner the molecular chain can proceed to lengthen.
The nucleic acid molecules, DNA (dreoxyribosc nucleic acid) and RNA (ribose nucleic acid) are chains made up of single links of nucleotides. Each nucleotidc in turn is made up of a sugar, a base, and a phosphate. In the case of DNA.the bases are adeninc, guanine, cytosine and thymine. RNA has the same bases except that the cytosine is replaced by uracil and the sugar deoxyribose of DNA is replaced by ribose. Adenine and guaninc are known as purines while cytasinc, thymine and uracil are pyrimidines.
The chemical constituents of all organisms are twenty acids, two sugars, and one phosphate. They are sometimes characterized as the ^alphabet of life.'58 a metaphor that is misleading because it tends to ignore the sharp qualitative distinction between these molecular con* stituents and the living, organic structure of which they arc a part. Such a characterization tends to reduce the study of life and its origin to an investigation of the quantitative increase in complexity of its constituent molecules. Engels who formulated that life was the mode of existence of protein bodies characterized by the constant self-renewal of their constituents, emphasized the importance of recognizing that life could never be reduced to mere chemical constituents.4
*The mature work ofOparin emphasized this scientific recognition •with growing sharpness and clarity. His 1924 hypothesis, which argued that there was no impassable barrier between the living and the nonliving, was a signficant blow to idealism in the study of the origin of li^e. In his 1936 book, Oparin made a real advance by demarcating his standpoint from that of scientists who saw living matter as nothing basically different from non-living matter.6 The publication of Engels's Dialectics of Nature in 1925 had a profound and clarifying influence on the development of Oparin's understand ing of the nature of life and its origin.