Name: RNA World
Uploaded: 2019-07-19
Duration: 5 min 49 s
Description: We know our DNA stores information, and the RNA reads it and transmits it. But which one appeared first? Let’s find out how this really works.

Question

The evidence used by Watson and Crick in building a model of DNA included data from an American chemist, Erwin Chargaff. Some relevant data are shown in the given table. What is a simple pattern in the base ratios?

Source of DNA	Adenine %	Guanine %	Thymine %	Cytosine %
Human (mammal)	30.9	19.9	29.4	19.8
Chicken (bird)	28.8	20.5	29.2	21.5
Salmon (fish)	29.7	20.8	29.1	20.4
Locust (insect)	29.3	20.5	29.3	20.7
Wheat (plant)	27.3	22.7	27.1	22.8
E. coli (bacterium)	24.7	26.0	23.6	25.7
Phage X1 74 (virus)	24.6	24.1	32.7	18.5

Accepted Answer

Watson and Crick used various available data and evidence to explain the structure of DNA through their model. The data used from Chargaff's table represents the sum total amount of different bases in a given species is 100. It indicates the complementary base pairing rule, that is, purines (guanine and adenine) present on one strand always pair with the pyrimidines (thymine and cytosine) on the complementary strand in a double-helical DNA molecule through the hydrogen bonds. The amount of a purine, for example, adenine, is always equal to the amount of pyrimidine with which it pairs (base ratio), that is, thymine.

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