Nitrogenous Base

ScienceTopping | Oct 4, 2021

Nitrogenous Bases on DNA

Adenine, thymine and uracil are purines; guanine and cytosine are pyrimidines.

IMAGE BY Magladem96, CC BY-SA 3.0/WIKIMEDIA COMMONS

Nitrogenous base is an organic molecule that contains the element nitrogen, N and functions as a base in chemical reactions. There are two main types of nitrogenous bases, which are

purines
pyrimidines

Purines are nitrogenous bases with two rings in their chemical structures, while pyrimidines are those with one ring. This indicates that purines have larger molecular size compared to pyrimidines.

Up to this point, it's time to look at the actual nitrogenous bases. How many are there?

There are five nitrogenous bases, namely adenine (A), thymine (T), guanine (G), cytosine (C) and uracil (U). Adenine, thymine and uracil belong to the group of purines, while guanine and cytosine are pyrimidines. Here comes the most significant part that must be memorised — the pairing system. In general review, purines pair with their complementary pyrimidines. More specifically, adenine pairs with thymine or uracil, while guanine pairs with cytosine. Always bear in mind that thymine is the substitute of uracil and vice versa. Thymine only presents in DNA, and uracil substitutes thymine in RNA. This is one of the major differences between DNA and RNA.

After understanding the pairing system, the number of chemical bonds formed by each base is another important point. Adenine forms two chemical bonds with thymine in DNA and uracil in RNA; Guanine forms three chemical bonds with cytosine. Do you still remember the chemical bonds formed between two nitrogenous bases in DNA? The chemical bonds are hydrogen bonds.

Chemical Bonds between Bases

In DNA, adenine forms two H bonds with thymine; guanine forms three H bonds with cytosine.

IMAGE BY Boumphreyfr, CC BY-SA 3.0/WIKIMEDIA COMMONS

Nitrogenous base is just one of the three components in DNA and RNA. DNA and RNA are made up of three main components, which are phosphate group, sugar and nitrogenous bases.

The chemical formula of each nitrogenous base is as follows.

Nitrogenous Base	Chemical Formula
Adenine	C₅H₅N₅
Thymine	C₅H₆N₂O₂
Uracil	C₄H₄N₄O₂
Guanine	C₅H₅N₅O
Cytosine	C₄H₅N₃O

To sum up, always have this formula in mind, A–T or A–U and G–C, whereby A pairs with T or U, while G pairs with C. With that, adenine is the complementary base of thymine or uracil, while guanine is the complementary base of cytosine.

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