Chemical Constituents of Nucleic Acid
Nucleic Acid
Nucleic acids are the most important and essential group of complex organic substances in living things. They are polymers of nucleotides. The principal nucleic acids, DNA, and RNA are the carriers of hereditary information and control the synthesis of proteins.
Nucleic acid was first isolated in 1869 by a Swiss physician, Fredrick Miescher from the nucleus of pus cells and sperms of salmon fish. He named it nuclein (because first recorded in the nucleus), later their acidic nature was observed (due to the presence of phosphoric acid), and were named nucleic acids.
Jones in 1920 proved the fact that there are two types of nucleic acids, i.e. deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
2.6.1 Chemical constituents of nucleic acid
As already described nucleic acids are polymeric organic molecules that are polymerized by the condensation of monomeric units called nucleotides. Nucleic acids despite their structural and functional diversity exhibit a constant chemical
composition.
Structure of nucleotides:
The partial hydrolysis of nucleic acids yields compounds known as nucleotides or nucleosides while complete hydrolysis yields a mixture of bases, pentose sugars, and phosphate ions.
DNA is made up of deoxyribonucleotides while RNA is composed of
ribonucleotides.
Bases:
The base is a nitrogen-containing heterocyclic organic molecule. There are two main types of bases in nucleic acids. i.e. pyrimidine and purine.
Pyrimidine Bases:
ring-like structure, These consist of nitrogen-containing six-corner monocyclic. (molecular formula is (N,C,). Three major types of bases are derived from the parent pyrimidine bases i.e. thymine, cytosine, and uracil.
Purine bases:
These are the second type of nitrogen-containing heterocyclic organic molecules that consist of two cycles. It is a member bicyclic molecule (N, C,). They are of two types, i.e., adenine and guanine.
Pentose sugars:
Two types of 5 carbon-containing pentose sugars are yielded during complete hydrolysis of nucleic acids i.e. deoxyribose (CH100,) from DNA and ribose (C, H,, Os) from RNA.
Phosphoric Acid:
Phosphoric Acid (H, PO,) can develop ester linkage with the hydroxyl group (OH) of pentose sugar.
Phosphodiester linkage:
In a typical nucleotide, the nitrogenous base is always attached to carbon one of pentose sugar while phosphoric acid (in a chain) is attached to carbon three of pentose sugar in front and to carbon five of pentose sugar behind it. Since phosphate forms a double ester linkage with pentose sugar. Thus the linkage is called phosphodiester linkage.
Nucleosides:
Nucleoside is formed when a nitrogen-containing base is linked with a pentose sugar. The bond that combines the base with sugar is called a glucosidic bond.
Nucleotides:
A nucleoside and phosphoric acid combine to form a nucleotide, which in the free state exists as either monophosphate, diphosphate, or triphosphate esters.
Mononucleotide:
ATP, cyclic AMP, and cyclic GMP are made up of one nucleotide. Chemical analysis of ATP reveals that it consists of adenine, ribose, and three phosphate groups. Adenine reacts with ribose to form a nucleoside called adenosine.
One, two, or three molecules of phosphoric acid react with adenosine by condensation reaction to form nucleotide, known as adenosine monophosphate (AMP), adenosine diphosphate hate (ADP), and adenosine triphosphate (ATP) respectively.
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