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

Sugar

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.

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

DNA

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

                            Prokaryote：nucleoid，

                            Plasmid

                            Virus

• 

RNA

• 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

   mRNA

• 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.

tRNA

• 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. tRNA^Ala )

rRNA

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

• 

Also have a look on:

The History of Nucleic Acids