“An organic substance present in the nucleus of a living cell helps in storing and transferring information is known as the nucleic acid.” 


DNA and RNA are the two types of nucleic acid present in all organisms (RNA is some viruses). 

Although the term “nucleic acid” was coined by Richard Altmann in 1889, it is actually discovered by Friedrich Miescher in 1869. He named it nuclein. 

 The actual structure of one of the nucleic acid- DNA was determined by Watson and Crick in 1953. 

We have a lot of material and information on DNA and RNA on our blog, henceforth we are not discussing it here. Though both are the nucleic acid, we will discuss the structure and function of nucleic acid in general here. 

The nucleic acid in the form of either DNA or RNA is present in all cells in all organism on the planet earth, no one can live without it. 

Structure of nucleic acid: 

In general, either DNA or RNA- nucleic acids are made up of the three major components- sugar, phosphate and nitrogenous bases. 

Purines and pyrimidines are present as nitrogenous bases in DNA while ribose and deoxyribose are present in RNA and DNA respectively. 

If you want to learn more about how the DNA is different from the RNA, please read our amazing article: DNA vs RNA. 

The nucleic acid is a complex molecule contains a long chain of biomolecules, organic in nature. it is made up of millions of monomer units, we can say that “nucleic acid is a biopolymer”. 

The nucleic acid is a long chain of nucleotides called polynucleotide chain which encodes a particular protein. 

The monomer of nucleic acid:

Obviously, the monomer of nucleic acid is a single unit of nucleotide. 

Mono- “one” + mer- “part”

A sugar, nitrogenous base and phosphate are collectively called as a nucleotide. While the nucleic acid without phosphate is termed as nucleosides. 

The structure of nucleotide and nucleoside.

The structure of nucleotide and nucleoside.

Remember: 

Base and nucleotide are different. When we call base pairing, it simply means one nitrogenous base binds to another complementary nitrogenous base on another strand with hydrogen bonds. 

But when we call nucleotide, it is a unit of sugar + base + phosphate binds to an adjacent nucleotide with the phosphodiester bond. See the image below, 

The pictorial illustration of the phosphodiester bonds between the nucleotides of RNA and hydrogen bonds between the two strands of DNA.

The pictorial illustration of the phosphodiester bonds between the nucleotides of RNA and hydrogen bonds between the two strands of DNA.

Interestingly, some nucleic acid monomers are also found on the surface of meteorites. Scientists believe that the nucleic acid polymer is formed from this monomer by natural events and that might be a reason for the evolution of life on earth. 

However, scientific evidence is not available to support this. 

Dimer of nucleic acid: 

When a monomer of nucleic acid- nucleotide binds with the adjacent nucleotide with a phosphodiester bond it is called a dimer of nucleic acid or dinucleotide. 

Similarly, when three nucleotides join together by the phosphodiester bond it is called trinucleotides. 

A trinucleotide repeat is present prevalently in the genome and abnormal growth of it causes some serious genetic problem. 

One of the common genetic disorder Huntington’s disease is originated due to the abnormal growth of tri-nucleotide repeat CAG. 

Interestingly dinucleotide repeats are also found in a genome- a type of tandem repeats responsible for hereditary nonpolyposis colon cancer is a dinucleotide repeat.

NAD (Nicotinamide adenine dinucleotide)- a type of dinucleotide functions as a cofactor in metabolic reactions. Two nucleotides adenine and nicotinamide join together by a phosphodiester bond and forms NAD.

The polymer of nucleic acid: 

A long chain of nucleotide monomers is called a polynucleotide chain (a polymer of nucleic acid). 

Poly- “many” + mer- “part”.

Our DNA and RNA are made up of the polynucleotide chain. 

A specific region of DNA which encodes a specific protein is known as a gene. 

Related articles:

  1. DNA: Deoxyribose nucleic acid 
  2. RNA: Ribose nucleic acid

The function of nucleic acid: 

The function of nucleic acid is very clear, it inherited or transfer information from one cell to another cell and hence from one generation to another. 

All the information of an organism is encoded in each monomer of nucleic acid. Each specific information is present on one particular polymer of it called a gene- a functional piece of DNA.

However, ~97% of our DNA unable to encode any protein.

Our cell is like a computer and a nucleic acid is a storage unit, used to store and transfer information just like the hard disk of our computer. Therefore we can say that every single monomer of nucleic acid is a storage unit (just like every byte of computer memory) 

The computer program works on the binary language of 0 and 1 while our nucleic acid- DNA  stores information in A, T, G and C. Three of the four nucleotides forms a codon, specifically called as a “triplet codon”. 

Each triplet codon forms a monomer of amino acid. 

Different triplet codon forms a long chain of amino acids called a protein. And that is how the entire mechanism works. 

Although storing and transferring information is the main function of nucleic acid, replication, transcription and translation is a way to do this. 

By replication, the DNA (one of the types of nucleic acid) copy the information, thus a DNA replicates or creates the exact same polynucleotide chain and inherited it to daughter cells.  

By doing transcription, a messenger RNA forms from the DNA from which only contains the coding information. 

Through the translation, the mRNA produces a protein. 

The nucleic acid also protects the genetic code from the enzymatic lysis and helps to inherit the exact copy of it. 

Besides this, our energy source Adenosine triphosphate (ATP) and guanosine triphosphate (GTP) are nucleotides- provides energy for doing various metabolic activities. 

GTP also plays an important role in G-protein mediated cell signalling. 

Genetic code: 

A bundle of three nucleotides encode one amino acid (trinucleotide or three nucleotides, not three base pairs). 

After the end of transcription, an mRNA is formed which only have the long chain of nucleotide monomer that encodes amino acids. 

All the non-coding sequences are removed. 

The mDNA now moves from the nucleus to the cytoplasm at the site of translation- ribosome. 

From the bunch of each triplet codon, a long chain of amino acid is formed. A long chain of amino acid forms a protein. 

Properties of nucleic acid: 

  • It is acidic in nature. It accepts paired electrons and donates protons. 
  • The nucleic acid is overall negatively charged due to the presence of negative charge on the backbone of it. 
  • It does not have its own colour or odour. 
  • The nucleic acid is insoluble in alcohol thus can be precipitated using it. It can also be precipitated using HCl or acetic acid. 
  • It can be easily dissolved in hot water. 
  • A DNA is a double-stranded and antiparallel molecule so DNA is more stable than RNA.
Differences between DNA and RNA.

Graphical illustration of the major differences between DNA and RNA.

Synthetic nucleic acid and nucleotides: 

Scientists are using synthetic nucleic acid and nucleotides for various applications. The synthetic nucleic acid is used for gene therapy and gene transfer experiments in which a specific faulty/mutated part of the DNA is replaced by artificially synthesised DNA. 

It is also used for copying DNA during PCR. 

Synthetic nucleotides such as dNTPs and ddNTPs are applicable in Polymerase chain reaction and DNA sequencing, respectively for synthesizing DNA and doing various molecular biology experiments. 

Threose nucleic acid, locked nucleic acid, glycol nucleic acid and peptide-bound nucleic acid are several types of synthetic nucleic acid employed in various research applications. 

Conclusion: 

The basic structure of nucleic acid is unchanged in every organism, however, the order of nucleotide sequence is different in every organism. And that is the reason why we are different. 

Scientists are believed that the RNA is evolved before the DNA. Then why DNA is formed in nature is still a mystery for us.   

Quiz:

A monomer of nucleic acid is known as________

  1. nucleoside
  2. nucleotide
  3. polynucleotide
  4. nucleosome

Answer

2. Nucleotide.

Nucleic acid- RNA is a genetic material of_______

  1. retrovirus
  2. bacteria
  3. fungi
  4.  algae

Answer

1. retorvirus

A nucleic acid can be precipitated using____

  1. water
  2. phenol
  3. alcohol
  4. EDTA

Answer

3. Alcohol.

Resources: 

  1. Real D. (2016) Physical and Chemical Properties of Nucleic Acids. In: Micic M. (eds) Sample Preparation Techniques for Soil, Plant, and Animal Samples. Springer Protocols Handbooks. Humana Press, New York, NY.