All of you listen about the word- Nucleic acids! Many Question is always around us that are - What are Nucleic acids? What is functions of Nucleic acids? Structure of Nucleic acids etc. So, in this article let's take answer of one by one question.
What are Nucleic acids?
Study of nucleic acids is very exciting and interesting as these compounds are the substances of heredity. In every species, every generation resembles in many ways to there ancestors.
The inherent characters are transmitted by the nucleus of every cell. Nucleic acids resembles proteins even though chemically they are different. The polynucleotide chain (polyester chain) is the backbone of nucleic acid molecule.
It is an ester of phosphoric acid with sugar. In the nucleus of a cell, the chromosomes are made up of nucleoproteins which contain two types of nucleic acids, ribonucleic acid called RNA and deoxy ribonucleic acid DNA.
The structure of polynucleotide chain is given below:
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| Polynucleotide chain |
In RNA the sugar is D-ribose and in DNA D-2- deoxyribose, the sugars are in furanose forms.
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| Structure of Ribose |
2-deoxy means no -OH group at C-1 position. The sugar units are joined to phosphate through C3 and C5 hydroxyl groups. Heterocyclic bases are attached to C-1 of each sugar unit through beta linkage.
The heterocyclic bases in DNA are adenine and guanine containing purine ring and cytosine and thymine which contain pyrimidine ring. In RNA the heterocyclic bases are adenine, guanine, cytosine, and uracil.
Purines and pyrimidines:
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| Purines & Pyrimidines |
A base-sugar unit is called nucleoside and a base-sugar phosphoric acid unit is called nucleotide.
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| Nucleoside & Nucleotide |
Nucleotides are joined together through phosphate ester linkage. The proportion of heterocyclic bases and the sequence in which they follow each other along the polynucleotide chain differ from one kind of nucleic acid to another. This is called it's primary structure. In 1980 Sanger worked on nucleic acid and found loops of DNA molecule to form a gaint ring containig 5386 nucleotides.
In 1953 Waston and Crick reported structure of DNA as a helix. The two polynucleotide chains wound about each other by N-H-N stable hydrogen bonds to form double helix.
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| Double helix of DNA |
The two chains head in opposite direction and the helix is right handed. There are two types of bases purines and pyrimidines.
There is hydrogen bonding between the bases adenine and thymine and also between guanine and cytosine. This is secondary structure.
Hydrogen bonding between other pairs of bases would not allow them to fit into double helical structure. The two polynucleotide chains are thus not identical but they are complementary.
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| DNA & RNA |
In the secondary structure of RNA the helixes are of single strand. The structure of nucleic acid molecules determine the structure of proteins molecules.
What are the Functions of Nucleic acids?
Nucleic acids control heredity. DNA is the repository of the heredity information. The information is stored as sequence of bases A, G, T and C. DNA after preserving the information, uses it by replication and the duplicate identical DNA are synthesized. They also control the synthesis of proteins.
There are three types of RNA, called messenger RNA, which carries the message to the ribosomes, ribosomal RNA where synthesis of protein takes place and transport RNA. The messenger RNA calls up the ribosomal RNA where synthesis of protein takes place and transport RNA. The messenger RNA calls up the series of transport RNA molecules which contain particular amino acids.
The order in which the transport RNA are called up by messenger RNA depends upon the sequence of bases of messenger RNA chains. There are different codes of amino acids like GAU, UUU, GUG, CUU, CUC, etc.
An error in reading of the code will cause change in amino acid sequence resulting into production of defective proteins and sometimes increase in developing cancer cells.
