Nucleic Acids

Introduction

Nucleic acids come under the category of macromolecules that are made up of repeating units of polymers. The two most important and known macromolecules are DNA and RNA. The nucleic acid helps in the storage of genetic information and then transfers it to the next generation. DNA helps in encoding the information that the cell needs for the making of proteins while RNA is found in various forms that helps in the synthesis of proteins. The term nucleic acid came into existence from their origin since they were acidic in nature and were isolated from the nucleus. They are highly stable proteins.

Types of Nucleic acids

Nucleic acid was first discovered from the nuclei of the pus cells by Friedrich Miescher. The nucleic acids are of two types: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA) that belong to the family of biopolymers. Nucleic acids are found in almost all living organisms including bacteria, archaea, viruses and inside cell organelles of eukaryotic cells like chloroplasts and mitochondria. Except for some red blood cells that are mature, both the DNA and the RNA are found in all living beings, while in the viruses either DNA or RNA is present. Nucleic acids can be generated artificially in the laboratory with the help of various enzymes called DNA and RNA polymerases and the process is called solid-phase chemical synthesis. The process of peptide nucleic acid helps in the synthesis of the altered nucleic acids that are not found in nature generally.

Structure of Nucleic acid

Nucleic acids are generally very large molecules out of which DNA is the largest molecule. The nucleotides are the monomeric unit in the nucleic acid that is composed of three main constituents: – a five-carbon sugar, a nitrogenous base and phosphoric acid. The nitrogenous bases have a heterocyclic structure that is aromatic molecules. There are two types of nitrogenous bases found in nucleic acids which are purines and pyrimidines. Adenine and guanine are the two types of purines while thymine, cytosine, or uracil are the three types of pyrimidines.

Phosphate group

The phosphate group is composed of a phosphorus atom that consists of four negatively charged oxygen atoms that are attached to it.

5-Carbon sugar

It is also known as pentose sugar that includes both the ribose and the deoxyribose found in the nucleic acid. They both have five carbon atoms along with hydrogen atoms and hydroxyl groups and one oxygen atom. In the case of a ribose sugar, the hydroxyl groups are attached to the carbon atoms of the first, second and third number while in the case of the deoxyribose sugar the hydroxyl groups are attached to the carbon atom of the first and third number while to the second carbon number only a hydrogen atom is attached.

Nitrogen Base

In nucleic acid, the nitrogen atom acts as a base as it gives electrons to various molecules that results in the formation of new molecules. It can also create a ring structure to bind with carbon, hydrogen, and oxygen molecules. Ring structures are of two types: purines (double rings), and pyrimidines (single rings). Pyrimidines consist of cytosine, thymine, and uracil while purines consist of adenine and guanine. Purines are larger than pyrimidines, this size difference helps in determining the pairings in the strands of DNA.

Nucleic Acid Bonds

The glycosidic and the ester bonds are those bonds that help in holding the sugar, phosphorus, and nitrogen molecules together. The bonds between the first carbon atom of the 5-carbon sugar and the nitrogen atom of a ninth number of the nitrogenous base are called glycosidic bonds. The bond between the fifth carbon atom of the 5-carbon sugar and the phosphate group is called ester bonds. These bonds hold single nucleotides and also several nucleotides together that form the polynucleotides and result in the formation of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). These polynucleotide chains will be formed by the bonding of the fifth carbon atom in a 5-carbon sugar and the third carbon atom in the next 5- carbon sugar that results in the formation of the sugar-phosphate backbone. If the sugar on the polynucleotide chain is ribose then it will lead to the formation of RNA while for the formation of DNA deoxyribose sugar is present in its polynucleotide chains, the polynucleotide strands in DNA and held together with the help of a hydrogen bond but will be in an antiparallel manner. The linking of the purines and the pyrimidines are responsible due to the hydrogen bonds. The pairing of adenine to thymine and guanine to cytosine is termed as a complementary base pairing in DNA.

Structure of Double-stranded DNA

DNA is of various types, but the two most common types of DNA are:

B DNA

• The double strand of the long polynucleotide chain is coiled around the axis
• The two strands of the DNA are arranged in an antiparallel manner
• Nitrogenous bases like adenine base pairs with thymine while guanine base pairs with cytosine
• The hydrogen bonds between adenine and thymine formed are two while the hydrogen bonds formed in between guanine and cytosine are three in numbers

Z DNA

• The structure of this DNA is thinner in comparison to B DNA
• The bases of purine and pyrimidine are alternatingly arranged
• To make the structure of DNA stabilized it is constituted of high salt concentration

Denaturation of DNA

The two DNA strands are denatured or are separated when they are passed through severe conditions like high temperature, pH, etc. This process is called denaturation. The DNA can be regained to its original structure by the removal of denaturants like pH, temperature, etc. This process is called renaturation or annealing.

RNA

RNA is also known as ribonucleic acid that consists of a single-stranded structure and is found inside the cell of various life forms. They are mainly of three types:

(i) Messenger RNA (mRNA) : The most important function of mRNA is that it carries genetic codons (made up of three nucleotides) that result in the coding of the amino acids that results in the synthesis of proteins.

(ii) Transfer RNA (tRNA) : Their main function is the formation of protein.They carry amino acids to the appropriate ribosomes during the process of protein synthesis. Thus these are carrier molecules found in the cytoplasm of the living cells.

(iii) Ribosomal RNA (rRNA) : It is the main constituent of ribosomes and helps in establishing bonds between amino acids during protein synthesis.

Conclusion

Thus it is observed that nucleic acid is the essential part of all living beings and nucleotides act as the building block of both the DNA and the RNA. It is found in all the cells along with some viruses as well. Nucleic acids are responsible for performing several functions that include storage and processing of genetic information, cell creation, generation of energy cells, and protein building and synthesis. Although the functions of both the DNA and the RNA are different their structures are quite similar and have only a few fundamental differences that differentiate their molecular structures and makeup.