Molecular Biology

In recent times the most dramatic advances in biology are coming from the field of molecular biology. Although this title could describe any area of biochemistry, it is usually taken to represent the study of processes involving genetic material that controls the activity and destiny of every individual cell. Genetic processes determine how cells differentiate into brain cells and stomach cells. Genetic control ensures that the brain cells do not secrete hydrochloric acid, as the stomach cells do.

It may seem incredible that the 23 DNA molecules in the haploid human genome can contain enough information to describe a human being completely. A simple comparison can be made to memory in a binary computer. Each of the 3.2 billion positions in the human genome can be occupied by one of four nucleotides. The number of possible combinations is 43 2 billion, which is 26 4 billion. Thus, the human genome has the information capacity of a 6.4-gigabyte binary memory. Think about how much memory would be required to specify the design of a human. The brain alone consists of about 1012 nerve cells, each with an average of 103 connections! A way around this paradoxical situation is to consider that the genes might only specify a set of rules that generate the structure rather than the detailed design of the structure. The new mathematical fields of chaos and complexity theory described in Section 2.5 show that exquisitely detailed structures can result from exceedingly simple rules.

Even more surprising is to discover that the human genome codes for only about 25,000 polypeptides (Table 6.1). Details of the remarkable mechanism by which the

TABLE 6.1 Amounts of Genetic Material in Several Organisms





Homo sapiens

3.2 billion


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