VIROLOGY—LILLY RESEARCH LABORATORIES 527 
duction but also to determine the specificity of a protein molecule, i.e., 
the enzyme. 
STRUCTURE OF GENETIC MATERIAL 
What is transmitted in us from one generation to the next is not 
a characteristic eye pigment or blood type. Rather, it is a set of 
factors in chromosomes which are able to influence the activities of 
cells so that certain substances responsible for eye pigment or blood 
type are produced. 
Current research indicates that chromosomes are largely composed 
of DNA,? which suggests that this substance is a major constituent 
of genes. In fact, we can say that DNA, the basic stuff of all cell 
nuclei, is the sole carrier of genetic information in all organisms 
(except in small viruses, where RNA appears instead). The word 
“information” as used here means that genetic material tells the repli- 
cating cell what its characteristics are to be. This information is in 
a chemical “code” in the structural form of the molecule. 
In spite of the complexity of its structure, the only variables in 
DNA are the purine, or pyrimidine, bases (adenine, guanine, thymine, 
cytosine), which are constant in any particular species. It appears 
that they are probably arranged in a definite sequence—which has 
been called the genetic code. 
Each time a cell divides, an exact copy of genetic information must 
be made in order to insure continuity. Therefore, much interest is 
shown in structural features. 
DNA would seem to be a double helix with the bases in each chain 
in a complementary sequence (pl. 3, fig.1). The two chains separate 
and make a duplicate of themselves, each offspring being an exact 
copy (pl. 3, fig. 2) 4 
RNA, not DNA, controls protein synthesis in the cell and may carry 
genetic information from nucleus to cytoplasm (5). Its structure is 
not completely understood. 
Most protein is probably made in the cytoplasm, where the point 
of polymerization seems to have been traced to small spherical 
particles known as microsomes. These particles resemble spherical 
viruses in shape and composition. “This suggests that a virus in- 
fection may be equivalent to the injection of an apparatus for the 
manufacture of the wrong protein” (6). 
The matter of genetic mutations, important in virology (such as 
the development of new virulent strains of influenza virus) as well 
as in clinical medicine, may also be explained in simple terms as the 
formation of an abnormal protein. 
*Sperm with half the chromosomes of a normal cell has about half the amount of DNA. 
“DNA can be extracted and transferred to another strain of bacteria and thus produces 
genetic transformation. When this transfer is made through infection by phage, it is 
known as transduction. The recent award of the Nobel Prize in Medicine went to Drs. 
Lederberg, Beadle, and Tatum for discoveries along these lines. 
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