- DNA – Deoxy ribo Nucleic Acid act as cellular library that contains necessary information for building cells and tissues of an organism.
- RNA – Ribo Nucleic Acid has pivotal role in protein synthesis.
Structure of DNA and RNA composed of multiple chemical units(polymer) of single chemical units(monomers) called Nucleotides.
- DNA : composed of several hundred million nucleotides.
- RNA : composed of hundred to thousands of nucleotides.
DNA and RNA consist of four types of nucleotides which is linked through phosphoester bond to a five carbon sugar molecule(pentose) that in turn linked to a base.
Difference between DNA and RNA :
- Pentose is ribose in case of RNA and deoxyribose in case of DNA.
- Other difference can be observed through its bases.Both DNA and RNA consist of adenine,guanine and cytosine but thymine only found in DNA and uracil in RNA.
Single letter codes are used for convenience in writing long sequences.
- Adenine => A.
- Guanine => G .
- Cytosine => C .
- Thymine => T.
- Uracil => U.
Nucleic acid bases are heterocyclic compounds with nitrogen and carbon in ring structure.Based on this ring structure nucleic acids bases are classified into purines(fused ring structure) and pyrimidines(single ring structure).
- Purines: adenine and guanine.
- Pyrimidines: cytosine, thymine and uracil.
DNA is a Double helical structure:
In 1953 James D. Watson and Francis H. C. Crick proposed that DNA is a double helical structure using x-ray diffraction pattern and cautious model building approach.DNA consist of polynucleotide strand wind together to form “double helix” structure.some important features of DNA double helical structure are
- Two sugar phosphate backbones on outside and he bases projects inside.Adjoining bases present in each strand stack on the top of one another in parallel planes.
- Orientation of two strands is anti-parallel(i.e 5’ –> 3’ direction are opposite).
- Regular base pairing : Adenine with Thymine by two hydrogen bonds and Guanine with Cytosine by three hydrogen bonds.This is called “Watson-crick base pairs”.
- Size, shape and chemical composition plays a major role in complementary base pairing.
- Grooves : Strand backbones are nearer on one side of the helix than other. Major groove represents the backbone is far apart and Minor groove represents that backbone is close to each other.Significance of these grooves is certain proteins binds to DNA to alter its structure or regulate replication or transcription. DNA binding proteins mostly binds to major groove because backbone are far apart thereby giving way for binding.
These nucleic acids consist of information for controlling hereditary traits of an organism and this unit is termed as “Genes”. During transcription information stored DNA is transferred to RNA(Ribo Nucleic Acid), that in turn has three important roles in synthesizing protein.
- mRNA(messenger RNA) carries information from DNA(transcription) regarding order of amino acids during protein synthesis(translation).
- Information from mRNA is interpreted by other type of RNA called tRNA (transfer RNA).
- Above process is aided by the third type of RNA called as rRNA(ribosomal RNA). As the correct amino acid brought into sequence using tRNA are then linked by peptide bonds to form protein and Enzyme.
Thus Nucleic acids play a vital role in maintaining the hereditary traits as DNA and RNA.