Classification, Distribution and Composition of Nucleic acids

Classification of nucleic acids

Nucleic acids are named because:

  • found in nucleus of cells
  • Later on discovered outside the nucleus
  •    DNA: Deoxyribonucleic Acid
  •    RNA: Ribonucleic Acid

Composition of nucleic acids

  • Elemental composition:  carbon, hydrogen, oxygen, nitrogen, phosphorous.
  • Linear polymers of nucleotides (polynucleotides)
  • Their building blocks are Nucleotides

Nucleotides are energy rich compounds that drive metabolic process in cell.

 Nucleotide  = nucleoside + phosphate

Each nucleotide consists of three compounds:

  • Purine or Pyrimidine nucleobase (Nitrogenous base)
  • Pentose sugar
  • Phosphate group

Nitrogenous bases

Two types of nitrogenous bases: Purine and Pyrimidine Derivative

  • Purine derivatives:  Adenine and Guanine
  • Pyrimidine derivative:  Uracil, Thymine and Cytosine

This base is linked to sugar moiety by same carbon used in sugar-sugar bond.

Nucleosides:  when ribose or 2-deoxyribose is combined with Purine or Pyrimidine base, Nucleoside is formed.

Nucleoside = pentose + bases

DNA:2-deoxyribose  + A, T, C, G

RNA:ribose + A, U, C, G

linkage : sugar C1-pyrimidine N1 and sugar C1-purine N9


5-C keto sugar or pentose

One possess 2-deoxyribose and other contain d-ribose

Both sugar are present in Furanose form and beta-configuration

Pentose sugar form esters with phosphoric acid and is called Phosphodiester bond.

How are the nitrogenous bases attached to the sugar-phosphate backbone of  DNA and RNA? | Socratic

Phosphoric acid

Molecular formula:  H3PO4

Contains 3 monovalent hydroxyl group and a divalent oxygen atom

All linked to pentavalent phosphorous atom

Types of nucleic acids


  • Deoxyribonucleic acid
  • Double stranded
  • Helical
  • Polymers of deoxyribonucleotides found in nucleus of the cell
  • Function:Storing the Genetic Code
  • DistributionEukaryote:nucleus (98%),organelle (2%);





  • Ribonucleic  acid
  • Single stranded
  • Non-helical
  • Polymers of ribonucleotides found in nucleus and cytoplasm of the cell
  • Function:  To transfer the genetic information from nucleus to cytoplasm for protein synthesis
  • Distribution: cytoplasm (90%), nucleus (10%);  virus
  • Type:  rRNA(ribosomal  RNA

                      mRNA(messenger  RNA)

                     tRNA(transfer  RNA)

                      other small RNA molecules


  • messenger RNA
  • 5%
  • carries genetic information from one or a few genes to a ribosome, where the corresponding proteins can be synthesized
  • it is a complementary copy of selected regions of the DNA.
  • It carries the genetic message from the nucleus to the cytoplasm and acts as the template for protein synthesis.


  • Transfer RNA
  • Also called Soluble RNA
  • 10-15%
  • Modified bases
  • Function:transfers a specific active amino acid to a growing polypeptide chain at the ribosome site of protein synthesis during translation
  • There is at least one tRNA species for every amino acid (eg. tRNAAla )


  • ribosome RNA
  • 80%
  • Function:the central component of the ribosome, associated with  protein synthesis.
  • Some of them have catalytic and coenzyme function as well.

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