How are the carbon and nitrogen atoms of the sugars, purines, and pyrimidines numbered?

Sugars are composed of a carbon backbone with oxygen and hydrogen atoms bonded to it. In sugars, the carbon atoms are numbered from the most oxidized carbon, which is typically an aldehyde or ketone. For example, in glucose (a hexose sugar), the carbons are numbered from 1 to 6, starting with the aldehyde carbon and ending at the terminal -CH2OH group.

Purines are heterocyclic aromatic organic compounds consisting of a pyrimidine ring fused to an imidazole ring. The two purine bases in DNA and RNA are adenine (A) and guanine (G). Purines have nine atoms in their bicyclic rings, five carbons, and four nitrogens. The atoms are numbered as follows: 1. Nitrogen atom in the pyrimidine ring, 2. Carbon atom in the pyrimidine ring connected to another nitrogen, 3. Carbon atom in the pyrimidine ring connected between two nitrogen atoms, 4. Nitrogen atom in the pyrimidine ring, 5. Carbon atom in the imidazole ring connected to nitrogen, 6. Nitrogen atom in the imidazole ring, 7. Carbon atom in the imidazole ring, 8. Nitrogen atom in the imidazole ring, and 9. Carbon atom in the imidazole ring connected to nitrogen.

Pyrimidines are aromatic heterocyclic organic compounds with a six-membered ring containing two nitrogen atoms and four carbon atoms. The three pyrimidine bases in DNA and RNA are cytosine (C), thymine (T), and uracil (U). The atoms in the pyrimidine ring are numbered as follows: 1. Nitrogen atom in the ring, 2. Carbon atom in the ring connected to two nitrogen atoms, 3. Nitrogen atom in the ring, 4. Carbon atom in the ring connected to the nitrogen atom, 5. Carbon atom in the ring, and 6. Carbon atom in the ring connected to the second nitrogen atom. In conclusion, the numbering of carbon and nitrogen atoms varies in sugars, purines, and pyrimidines. Understanding their numbering systems helps in identifying the atoms involved in various reactions and their structural and functional properties.