how we count the carbon number in the nitrogeneous bases and pentose sugar?

Answer 1

To count the carbon number in the nitrogenous bases and pentose sugar, you should locate the position of the carbon atom in the structure of the molecule. Here's a brief explanation for both:

1. Nitrogenous Bases (such as adenine, guanine, cytosine, thymine, and uracil):
In these bases, you can start numbering the carbon atoms from the nitrogen atom attached to the ring. Typically, you will have two rings in the bases: a pyrimidine ring (containing 6 atoms) or a purine ring (containing 9 atoms).

For pyrimidine bases, you start counting carbon atoms from the nitrogen atom to the right at the bottom of the ring. This nitrogen atom is usually numbered as carbon 1. The numbering continues clockwise around the ring, so the carbon atom just before the starting nitrogen atom is numbered as carbon 2, the next one as carbon 3, and so on until carbon 6.

For purine bases, the numbering starts from the nitrogen atom in the smaller ring (pyrimidine ring) and then continues through the larger ring (adenine, guanine). Similar to pyrimidines, the numbering starts from the nitrogen atom at the bottom right of the small ring, which is typically numbered as carbon 1. The numbering continues clockwise in the small ring, and once it reaches the large ring, it continues clockwise as well until it completes the numbering.

2. Pentose Sugar (ribose or deoxyribose):
The carbon numbering in the pentose sugar begins at the carbon attached to the oxygen atom at the top of the ring. This carbon is called the anomeric carbon (also known as carbon 1). The numbering proceeds counterclockwise around the ring until it reaches carbon 5.

It's important to note that in the pentose sugar ring, the carbon atoms are usually represented by a prime (') symbol (e.g., C1', C2', C3', C4', C5') to differentiate them from the carbons in the nitrogenous bases.

Remember to refer to the specific molecular structures to determine the precise numbering for each carbon atom in the nitrogenous bases and pentose sugar.