Structural model of human gene DNA

Bases are the derivatives of purines and pyrimidines and are the components of nucleic acids, nucleosides and nucleotides. The main bases of DNA and RNA are slightly different. The important difference is that thymine is the main pyrimidine base of DNA, which is rarely seen in RNA. In contrast, uracil is the main pyrimidine base of RNA and is rare in DNA.
In addition to the main bases, nucleic acids also contain some rare bases with very small amounts. The structure of rare bases is varied, most of which are methyl derivatives of major bases. TRNA often contains more rare bases, with some tRNA containing up to 10% of rare bases. Purine and pyrimidine bases are nearly planar molecules that are relatively insoluble in water: they have strong absorption in the ultraviolet region of about 260 nm.

1. What is the three-dimensional structure of DNA?

2. What are the basic units of DNA?

3. What principles do base pairs follow?

Experimental report:

Rule 1: in A double-stranded DNA molecule, A=T, G=C. A+G=T+C or A+C=T+G.
Five kinds of bases
Five kinds of bases
In other words, the total number of purine bases is equal to the total number of pyrimidines, each accounting for 50% of the total number of bases.
Rule 2: in a double-stranded DNA molecule, the ratio of the sum of two complementary pairs of bases is equal to the ratio of each single strand in the DNA molecule. (A1 + A2 + T1, T2)/(G1 + G2 + C1 + C2) = (A1 + T1)/(G1 + C1) = (A2 + T2)/(G2 + C2).
Rule 3: in one strand of DNA molecule, the ratio of the sum of two non-complementary pairs of bases is equal to the reciprocal of this ratio in the other complementary strand, that is, the ratio in one strand of DNA molecule is equal to the reciprocal of this ratio in its complementary strand. (A1 + G1)/(T1 + C1) = + C2 (T2)/(A2 + G2).
Rule 4: in a double-stranded DNA molecule, the ratio of two complementary bases to all bases is equal to the ratio of any single strand to that base, and is equal to the ratio of the transcribed mRNA to that ratio. Namely double-stranded (A + T) % % = (G + C) or any single (A + T) % or % = (G + C) mRNA in (A + U) or (G + C) % %.
Rule 5: the ratio of the sum of complementary pairs of bases (A+T)/(G+C) is different in DNA molecules of different organisms, which represents the specificity of each biological DNA molecule.