Heredity and Development Second Edition (1972) / Chapter Skim
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7 The Substance of Inheritance
7 The Substance of Inheritance
Pages 152-166
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From page 152... ...
When capsulated cells are grown on culture plates they form colonies that are smooth and shiny in appearance. Mutations that give rise to cells lacking capsules are infrequent but, since the bacteria are in such tremendous numbers, even rare mutations can easily be observed.
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From page 153... ...
Next Griffith made a double injection: his mice received living capsuleless Type II bacteria plus heat-killed capsulated Type II. On the basis of the data given so far, we might predict that the mice would remain healthy.
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From page 154... ...
Another experiment showed that mutation was not the explanation, and also shed new light on the problem. Once again the experiment consisted of giving the mice a double injection: living capsuleless bacteria plus dead capsulated bacteria.
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From page 155... ...
the polysaccharide ‘when added in chemically purified form, has not been found effective in causing transformation of non-capsulated organisms derived from Diplococcus of one Type into capsulated forms of the other Type. When non-capsulated cells change into the capsulated form they always acquire the property of producing the specific capsular substance.
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From page 156... ...
Avery, MacLeod, and McCarty reported that they had obtained the transforming substance in a highly purified state and had established its chemical nature beyond a reasonable doubt. They began with huge amounts of Type III cells, using in some experiments the cells from as many as 75 liters of culture medium.
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From page 157... ...
Avery, MacLeod, and McCarty concluded, The fact that trypsin, chymotrypsin, and ribonuclease had no effect on the transforming principle is further evidence that the substance is not ribonucleic acid or a protein susceptible to the action of tryptic enzymes.' Thus they were reasonably sure of some of the substances that the active principle could not be, but how could they prove the hypothesis
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From page 158... ...
Its biological activity was also quite impressive: transformation could be induced when the DNA was present in a concentration of one part in 600 million. The following quotation shows how the authors explained their observations that an extract of the DNA of Type III capsulated cells could cause Type II non-capsulated cells to start producing capsules that were specific to Type III.
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From page 159... ...
forms not alone by serological reactions but by the presence of a newly formed and visible capsule which is the immunological unit of type specificity and the accessory structure essential in determining the infective capacity of the microorganism in the animal body. It is particularly significant in the case of [the bacterial cells]
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From page 160... ...
Microorganisms known variously as the bacterial viruses, bacteriophages, or phages can attack bacterial cells and so disrupt the cell's metabolism that death results. In recent years, one bacterium and its many phage parasites have given important new insights into genetic mechanisms.
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From page 161... ...
It follows, therefore, that a biological system consisting of no more than a protein coat and a DNA core contains all the genetic information needed to direct a bacterial cell to make more T2 phage. These phage particles are only about one-fifth of a micron in length.
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From page 162... ...
The new phage was produced, of course, from the materials in the bacterial cells, which contained the radioactive markers. Thus in one group of phage the protein coats became marked with S35 and in the other group the DNA was marked with P32.
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From page 163... ...
In a few minutes the bacteria, plus phage, were put in a Waring blendor, the phage ripped from the bacterial cells, and then the cells and phage separated. Analysis of the cells and fraction containing the phage gave results precisely opposite to those observed with S35.
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From page 164... ...
Other investigators (including James D.Watson of whom we shall hear more shortly) had just reported that about 50 per cent of the P32 that first entered the bacterial cells was recovered in the daughter phage particles.
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From page 165... ...
These genes could ‘infect' bacterial cells in much the same way as phage infect E coli.
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From page 166... ...
1944. ‘Studies on the chemical nature of the substance inducing transformation of pneumococcal types.' Journal of Experimental Medicine 79:137–58.
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