Nucleic acids are important class of macromolecules found in all cells and main information-carrying molecules of the cells. DNA and RNA are the two main classes of nucleic acid.

A simple difference between DNA and RNA is given below in the tabular form:

Deoxyribonucleic acidRibonucleic acid
DNA is the hereditary material in an organism transfer the genetic code from the nucleus to the ribosomes to make proteins.
DNA is a double-stranded molecule consisting of a long chain of nucleotides form B form helix RNA usually is a single-strand helix consisting of shorter chains of nucleotides form A form helix
 DNA is found in the nucleus of a cell and in the mitochondria.RNA is found in the cytoplasm, nucleus, and in the ribosome.
 It has 2-deoxyribose.It has Ribose.
The base pairing within the DNA is G ≡C (Guanine pairs with Cytosine) A=T (Adenine pairs with Thymine).The base pairing is as follows: G ≡C (Guanine pairs with Cytosine) A=U (Adenine pairs with Uracil).
DNA replicate itselfRNA does not replicate on its own. It is synthesized by the DNAA.
DNA is susceptible to UV damage.RNA is relatively resistant to UV damage as compared to DNA
DNA polymerase is required for DNA replicationRNA polymerase helps in the synthesis of RNA from the DNA


DNA (deoxyribonucleic acid) is the genomic material in cells that contains the genetic information to make other cells and new organisms, located within chromosomes of the cell nucleus (where it is called nuclear DNA). Mitochondria also contain a small amount of DNA where it is called mitochondrial DNA or mtDNA. DNA was first time discovered in 1869 by Swiss chemist Friedrich Miescher. In 1953 James Watson and Francis Crick, explain the structure of DNA which is the Watson and Crick model of DNA.

The building blocks of DNA is called nucleotide which is composed of three components

  • Sugar group (deoxyribose): Form the backbone of the DNA
  • Phosphate group
  • Nitrogen base: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) 

DNA is a double-stranded helix, with the two nucleotide strands connected by hydrogen bonds. Adenine (A) bases are always paired with thymine (T), and cytosine (C) are always paired with Guanin (G). These bases are connected via the hydrogen bonding Cytosine and Guanine are held together by three hydrogen bonds while Adenine (A) and thymine (T) are held together by two hydrogen bonds.

The sequence of these four nitrogenous bases along the backbone encodes information. The backbones of the DNA are made of sugars and phosphate groups joined by ester bonds. One complete turn of the double helix has 10 base pairs and approximately 3.4 nm long. Thus, the distance between two consecutive base pairs is 0.34 nm.

The DNA double helix is anti-parallel, which means that the 5′ end (has a terminal phosphate group) of one strand is paired with the 3′ end (has the terminal hydroxyl group) of its complementary strand (and vice versa).

The configuration of the DNA molecule is highly stable, allowing it to act as a template for the replication also known as semi-conservative replication, during which DNA makes a copy of itself, as well as act as a template for the production (transcription) of the related RNA (ribonucleic acid) molecule. A basic physical and function segment of DNA that codes for the cell’s synthesis of a specific protein is called a gene. The important property of DNA is to make copies of itself.

Types of DNA

There are following types of DNA on the basis of structural confirmation

  1. A-DNA: It is a right-handed double helix DNA that is rare structural confirmation that DNA adopted under the dehydrating condition. It is formed by the B-DNA. A-DNA protects the DNA during extreme condition such as desiccation
  2. B-DNA: B-DNA is the most common and prominent DNA conformation and is a right-handed helix. Majority of DNA prefer to occur in a B type conformation under normal physiological conditions.
  3. Z-DNA: Z-DNA is a left-handed DNA confirmation in which the double helix winds to the left in a zig-zag pattern. It is found upstream of the start site of a gene and play role in the regulation of the gene expression.

Noncoding DNA and Coding DNA

The DNA that doesn’t code for the protein is called the noncoding DNA while Coding DNA is responsible for harboring the specific DNA sequences that encode instructions for making proteins. The noncoding DNA referred to as regulatory DNA which determine when and where some genes are transcribed.

Function of the DNA

DNA involved in

  • DNA is the genetic material carries and store the genetic information
  • Replication process: Transferring the genetic information from one cell to its daughters and from one generation to the next and equal distribution of DNA during the cell division
  • Mutations: The changes which occur in the DNA sequences due to some chemical and physical mutagens
  • Transcription: DNA helps in the synthesis of RNA
  • DNA Fingerprinting: laboratory technique used for criminal investigation
  • Gene Therapy: use to treat or prevents the disease by removing or changing the defecting gene
  • Cellular Metabolism


Ribonucleic acid (RNA) is an important biological macromolecule present in all cells that carrying the messenger instructions from DNA for protein synthesis. The single-stranded structure of RNA allows this molecule to fold back on itself and form various stable secondary structures like hairpin loops which are stabilized by intramolecular hydrogen bonds between complementary bases.

Unlike DNA, RNA is the single stranded. RNA has the similar structure to DNA but the one nitrogenous base out of four nitrogenous bases are different in the RNA from the DNA. The nitrogenous bases present in RNA are adenine (A), cytosine (C), uracil (U), and guanine (G).  Ribose sugar is present in RNA instead of deoxyribose (ribose contains one more hydroxyl group on the second carbon).

RNA is synthesized by the RNA polymerase using the DNA strand as a template through a process known as transcription. RNA can serve as an enzyme itself called ribozyme to perform a catalytic activity in the ribosome by rRNA mediates amino acid addition to growing proteins. Other ribozymes include small nuclear RNAs (snRNAs) (splice mRNA into usable forms), and M1 RNA, one of the first known ribozymes.

Types of RNA

 Messenger RNA (mRNA): mRNA is short, unstable, single-stranded RNA. mRNA carries genetic codes from the DNA in the nucleus to ribosomes in the form of triplets of nucleotides called codons. mRNA comprises 5% of the total RNA.

 Transfer RNA (tRNA): tRNA is the smallest of three types of RNA and an essential component of translation. tRNA is short RNA that contains 70-90 nucleotides but stable RNA with extensive intramolecular base pairing. tRNA contains two binding sites one is an amino acid binding site and the other is an mRNA binding site. tRNA carries the amino acid to the site of protein synthesis in the ribosome

 Ribosomal RNA (rRNA): rRNA is a longer, stable RNA molecule composing 60% of the ribosome’s mass and accounts for 80% of the total RNA. The main function of rRNA is to ensure the proper alignment of mRNA, tRNA, and ribosome during protein synthesis. It catalyzes peptide bond formation between amino acids during protein synthesis.

Function of RNA

  • In many RNA viruses it serves as hereditary information 
  • RNA is the part of central dogma and involved in the process of translation
  • RNA act as ribozyme
Sana Riaz

Sana has just completed her MPhil in Microbiology. She loves reading books and the latest discoveries in sciences.

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