Which nitrogenous bases are pyrimidines

Pyrimidines are aromatic nitrogen heterocycles with a structure similar to benzene but containing two nitrogen atoms at the 1 and 3 positions of the ring. Pyrimidines along with purines serve as the informational monomers of RNA Skip to main content Skip to table of contents. This service is more advanced with JavaScript available. Encyclopedia of Astrobiology Edition. Irvine, Daniele L. Pinti, Michel Viso. Contents Search. Pyrimidine Base. Authors Authors and affiliations Michael P.

How to cite. Keywords Cytosine , nitrogen heterocycle, thymine , uracil. Figure 2. Scientist Rosalind Franklin discovered b the X-ray diffraction pattern of DNA, which helped to elucidate its double helix structure.

Watson and Crick proposed that DNA is made up of two strands that are twisted around each other to form a right-handed helix. Thus, adenine and thymine are complementary base pairs, and cytosine and guanine are also complementary base pairs.

The base pairs are stabilized by hydrogen bonds: adenine and thymine form two hydrogen bonds and cytosine and guanine form three hydrogen bonds. The sugar and phosphate of the nucleotides form the backbone of the structure, whereas the nitrogenous bases are stacked inside, like the rungs of a ladder. Each base pair is separated from the next base pair by a distance of 0.

Therefore, 10 base pairs are present per turn of the helix. The diameter of the DNA double-helix is 2 nm, and it is uniform throughout. Only the pairing between a purine and pyrimidine and the antiparallel orientation of the two DNA strands can explain the uniform diameter.

The twisting of the two strands around each other results in the formation of uniformly spaced major and minor grooves Figure 3. Figure 3. DNA has a a double helix structure and b phosphodiester bonds. Improve this page Learn More. Skip to main content.

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