LEARNING OBJECTIVES
In this article, author has explained the introduction to nucleic acids their structure, biosynthesis and functions.
Definition
Table of Contents
A nucleic acid is a polymer of nucleotides that stores genetic information in the cell. Nucleic acids are also known as polynucleotides. It is a large molecule that is made of many small molecules called nucleotides.
There are two types of nucleic acids known; ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Nucleic acids are hereditary materials. DNA is responsible for the transmission of characteristics from one generation to the next.
Structure of nucleotides
Nucleic acids are polynucleotides that are composed of a long chain of molecules called nucleotides. Nucleotides are building blocks of nucleic acids. Each nucleotide is made of three components;
- Nitrogen-containing base
- Five carbon sugar (pentose sugar)
- Phosphate group
The nitrogenous bases are of two types; purines and pyrimidines. Purines consist of adenine and guanine while pyrimidines consist of cytosine, thymine, and uracil. The four bases adenine, guanine, cytosine, and thymine are present in all nucleic acids while uracil is only present in RNA.
The pentose sugar (deoxyribose) of DNA is different from the pentose sugar (ribose) of RNA as the hydroxyl group is absent on carbon number 2 in DNA.
If the phosphate group is absent then nucleotide is known as a nucleoside. The phosphate group acts as a bridge between two sugars by connecting the hydroxyl group of C5 of one sugar to the hydroxyl group of C3 of the next sugar. This linkage is known as a phosphodiester bond which is the same in both DNA and RNA.
Like proteins and carbohydrates, nucleic acids are also formed by the dehydration process. When nitrogenous bases are linked, a water molecule is eliminated.
Biosynthesis of nucleic acids
Nucleotides are synthesized from the precursors present in the cell. The ribose phosphate portion of both purines and pyrimidines is synthesized from glucose. This synthesis occurs via the pentose phosphate pathway. Firstly pyrimidine ring is synthesized and then it gets attached to the sugar-phosphate. After this two rings of purines are synthesized and attached to sugar phosphate. This happens during the assembly of adenine or guanine nucleosides. The end product is the nucleotide containing a nitrogenous base and phosphate attached to the C5 on the sugar.
Finally, the enzyme kinase adds two phosphate groups to form ribonucleotide triphosphate. The phosphates are donated by adenosine triphosphate (ATP). Ribonucleotide triphosphate acts as a precursor for the synthesis of RNA.
The hydroxyl group at the C2 is removed from the ribonucleoside diphosphate to give deoxyribonucleoside diphosphate. Another phosphate group from the ATP is added to the deoxyribonucleoside diphosphate by the other kinase enzyme. This forms deoxyribonucleotide triphosphate which acts as a precursor for the DNA.
The RNA is constantly being made and broken during normal cell metabolism. The nitrogenous bases purines and pyrimidines are used and reused to make more genetic materials.
Functions of nucleic acid
- Nucleic acids are necessary for all life forms and are present in all cells.
- The genetic information is stored in the nucleic acids.
- Nucleic acids are responsible for the synthesis of protein in our body.
- DNA is regarded as a reserve bank of genetic information.
- DNA is responsible for the unique identity of all the species over millions of years.
- Every aspect of cellular function is under the control of DNA.
- DNA consists of fundamental units of genetic information known as genes.
- Genes control the formation of a protein with help of RNA.
- The interrelationship between these three biomolecules makes the central dogma of molecular life.
- They are also known as the central dogma of life.
- DNA fingerprinting is used in the determination of paternity.
- It is also used for the identification of criminals.
- DNA fingerprinting plays a major role in biological evolution and genetics.