DNA is a polymer, and DNA solution is a polymer solution with high viscosity, which can be dyed green by methyl green. DNA can absorb ultraviolet (260nm), and the content of DNA can be determined by this characteristic. When nucleic acid denatures, the absorbance increases, which is called hyperchromic effect; When the denatured nucleic acid renaturates, the absorbance will return to the original level. Higher temperature, organic solvent, acid-base reagent, urea, amide, etc. Can cause DNA molecular denaturation, that is, the hydrogen bond between DNA double-stranded bases breaks and the double helix structure unwinds-also known as DNA unwinds.

The introduction of DNA double helix structure has opened the era of molecular biology, which has made the research on heredity go deep into the molecular level, and the "mystery of life" has been uncovered, and people have a clear understanding of the composition and transmission of genetic information. 1953, Watson and Crick discovered the double helix structure of DNA, which opened the era of molecular biology, made the study of heredity go deep into the molecular level, uncovered the "mystery of life", and people clearly understood the composition and transmission mode of genetic information. In the next 50 years, new disciplines such as molecular genetics, molecular immunology and cell biology have sprung up, which have clarified the mystery of life more clearly from the molecular point of view. DNA recombination technology has opened up a broad prospect for the research and application of bioengineering means.

Meaning:

The significance of the double helix model is not only that the structure of DNA molecules has been proved, but more importantly, it also suggests the replication mechanism of DNA: since adenine (a) is always paired with thymine (t) and ornithine (g) is always paired with cytosine (c), it shows that the base sequences of the two chains are complementary, as long as the base sequence of one chain is determined, the other is. Therefore, only one chain can be used as a template to synthesize and copy the other chain.