Which nitrogenous bases are purines pyrimidines

The nitrogenous base can be a purine, such as adenine A and guanine G , or a pyrimidine, such as cytosine C and thymine T. Uracil U is also a pyrimidine as seen in Figure 1 , but it only occurs in RNA, which we will talk more about later. Figure 1. Each nucleotide is made up of a sugar, a phosphate group, and a nitrogenous base.

The purines have a double ring structure with a six-membered ring fused to a five-membered ring. Pyrimidines are smaller in size; they have a single six-membered ring structure. The nucleotides combine with each other to produce phosphodiester bonds. Other scientists like Linus Pauling and Maurice Wilkins were also actively exploring this field.

Pauling previously had discovered the secondary structure of proteins using X-ray crystallography. Unfortunately, by then Franklin had died, and Nobel prizes are not awarded posthumously. 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.

A purine is a heterocyclic aromatic organic compound containing 4 nitrogen atoms. It contains two carbon rings, and is made of a pyrimidine ring fused to an imidazole ring.

A pyrimidine is a heterocyclic aromatic organic compound containing 2 nitrogen atoms. It contains only one carbon ring. Both purines and pyrimidines have the same function: they serve as a form of energy for cells, and are essential for production of DNA and RNA, proteins, starch, regulations of enzymes, cell signaling.

Useful mnemonics to remember these bases are:. Pyrimidines can be prepared in a lab using organic synthesis, such as through the Bigineli reaction. Share this comparison:. If you read this far, you should follow us:. Diffen LLC, n. Comparison chart Differences — Similarities —.

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