Chemical Nature of Genes 



301 



NH2 



NHo 



Deoxycytidine 3'-monophosphate 



Deoxycytidine 5'-monophosphate 



or 



Deoxycytidylic acid 



NH, 



OH 



Deoxyadenosine 5'-monophosphate 



or 



Deoxyadenylic acid 



Deoxyadenosine 3'-monophosphate 



FIGURE 33-8. Specific deoxyrihonucleutides. 



beck technique stains DNA purple (see p. 19), 

 while the methyl green method causes it to 

 stain green. Not only are these stains, when 

 applied properly, specific for DNA, but the 

 amount of staining is directly proportional 

 to the amount of DNA present. A given 

 amount of stain retained in the nucleus will 

 make a known quantitative change in the 

 amount of different wave lengths of light it 

 transmits, and this measurement can then be 



used to calculate the amount of DNA present. 

 When, under the m/croscope, such a stained 

 nucleus has different, appropriate, wave 

 lengths of light in the visible spectrum sent 

 through it, it is possible to determine, from 

 changes in the density of its /7/?o/c»graphs, a 

 measurement of its DNA content. From the 

 portions of words italicized you can under- 

 stand why this procedure is called micro- 

 spectrophotometry. 



