Purine and Pyrimidine Bases, Sugars, and Phosphoric Acid

Purines and pyrimidines are the classes of nucleotides forming the nucleic acid in a cell. They serve a primary role in the formation of DNA and RNA as genetic information storage, and also as an energy carrier, component of coenzyme, and cellular signal transduction. Sugars are five-carbon molecules that are essential parts of nucleotides. The sugars included in nucleic acid are called pentose sugars. The phosphate group completes the nucleotide.

Purines

Purines are organic compounds containing two heterocyclic rings which are usually water-soluble and contain nitrogen and carbon atoms. These can be classified as:

• Normal purines.

• Substituted purines.

• Tautomeric purines.

Purine bases

Purine bases are involved in the formation of DNA and RNA. There are two purines that makeup DNA and RNA, these are:

• Adenine: It can be called 6-aminopurine.

• Guanine: it can be called 6-oxy-2-aminopurine.

These bases form hydrogen bonds with the pyrimidine bases of opposite strand thymine and cytosine respectively in DNA while in RNA the adenine forms a hydrogen bond with uracil. Purines are larger than pyrimidines as purines have two rings, whereas pyrimidines only have one. Purine is composed of a five-membered nitrogen ring joined together with a six-membered nitrogen-containing ring. It can be found in the nucleus of animal and plant cells.

Pyrimidine 

Pyrimidine is an aromatic heterocyclic compound that is stable and ring-shaped. These have six-membered rings made of four carbon and two nitrogen atoms. As it has nitrogen, it comes under nitrogenous bases.

Pyrimidine bases

There are three pyrimidine bases found in nucleic acid. These are thymine, cytosine, and uracil. DNA has cytosine and thymine pyrimidine. These will form hydrogen bonds with purines i.e., adenine and guanine.

• RNA has uracil and cytosine pyrimidines which form bonds with adenine and guanine respectively.

Purines versus pyrimidines

• Purine and pyrimidine are distinguished by the following characteristics:

• Pyrimidines have just one carbon ring, while purines have two.

• When compared to pyrimidines, purines have greater melting and boiling points. The reason for this is that purine molecules have complicated and hefty melting and boiling points.

• Purines are key molecules in the biosynthesis of theophylline, theobromine, caffeine, and other chemical substances whereas Pyrimidines are not involved.

Sugars

The sugar found in nucleic acid is pentose sugar, also known as aldose sugar. It is a five atom carbon molecule which is a monosaccharide. In RNA the sugar molecule present is the ribose sugar while the sugar present in the DNA molecule is five-carbon, deoxyribose sugar. Both sugars are chemically distinct, with ribose having the chemical formula C5H10O5 and deoxyribose having the molecular formula C5H10O4. The 5′ and 3′ carbon OH groups in these sugars form bonds with phosphate groups, whereas the 1′ carbon OH groups form bonds with nitrogenous bases.

Phosphoric acid

Its formula is H3PO4. There are three reactive -OH groups in it. Using phosphodiester bonds, sugars and phosphoric acid produce the initial structure of nucleic acids such as DNA and RNA.

Formation of nucleic acid

Nucleic acid is a nucleotide polymer. A polynucleotide chain is formed when nucleotides join to create a nucleic acid backbone. A nucleotide is made up of three different parts:

• Nitrogenous bases.

• Pentose sugar.

• Phosphate group.

A sugar molecule with an attached phosphate group is connected to each nitrogenous base in a nucleotide.

DNA

Deoxyribonucleic acid, commonly known as DNA, is a double-stranded helix that contains an organism’s genetic information. It is responsible for the transmission of characters from one generation to another. Sugar and phosphate, which are found outside the helix, make up its backbone. The two strands of the helix run antiparallel to each other having nitrogenous bases in their interior part. There are hydrogen bonds that connect these bases. It makes a ladder-like structure.

RNA

RNA stands for ribonucleic acid. It has ribose sugar and is involved in the formation of protein. RNA usually has a single strand and is made of ribonucleotides connected by phosphodiester bonds. There are four different kinds of RNA:

Messenger RNA or mRNA: It carries messages from DNA.

Transfer RNA or tRNA: It is responsible for the transfer of amino acids during protein biosynthesis. Ribosomal RNA or rRNA: it is a given as the primary constituent of cell organelle ribosomes. Micro RNA or miRNA: it is the smallest RNA involved in gene expression.

Conclusion

Thus, here one can conclude that DNA and RNA are the two kinds of nucleic acids. These nucleic acids are formed by a pentose sugar, nitrogenous bases, and phosphate group. These sugar and phosphate groups are linked together by phosphodiester bonds and the bases of the complementary strands are joined together by double or triple hydrogen bonds. The nitrogenous bases are divided into purines and pyrimidines. Adenine (A) and guanine (G) are the bases present in purine molecules, while thymine, cytosine, and uracil bases are found to be present in the pyrimidine molecules. The presence of the bases A, G, C, and T stand for the synthesis of the double-helical DNA while replacing T with U form the basis for the RNA molecule.