Structure of DNA and RNA

DNA structure:

DNA or Deoxyribonucleic acid is a nucleic acid that preserves the genetic information required for cell structuring, development and functional purposes.

Chemically, DNA is a long polymer of individual units known as nucleotides. Each nucleotide is composed of a sugar and phosphate backbone formed by phosphodiester bonds. Attached to each sugar is one of four types of nitrogenous bases. The nitrogenous bases are either of a purine (adenine and guanidine) or a pyrimidine (cytosine and thymine) group. The two chains of the DNA double helix are held together by hydrogen bonds formed between these nitrogenous bases which are pointed inwards to the centre of the helix.

The hydrogen bonds are not formed randomly instead there is a characteristic pairing form known as complementary base pairing. One of the purine bases in one chain pairs with one of the pyrimidine bases in the other chain. Guanidine always pairs with cytosine while adenine always pairs with thymine.

The genetic code consists of 64 triplets of these DNA units, the nucleotides. These triplets are named codons. Most of the amino acids are encoded by more than one codon.

DNA

Double stranded polymer (helix) of polynucleotide chains.

Bind together by hydrogen bonds between the bases of the nucleotides in complementary manner. A=T and GΞC.

The two strands run antiparallel (in opposite direction). Thus one of them is running in the 5` to the 3` direction, and the other runs in the direction of the 3` to the 5` direction.

Note that transcription (reading the genetic code) occurs in the direction of the 5` to the 3` direction.

RNA

It is transcribed form the DNA into the form of a single strand polymer of nucleotide.

The pyrimidine Uracil replaces the thymine in DNA.

The pentose sugar is ribose.

It is less stable than DNA.

There are four main types: messenger mRNA, transfer tRNA, and ribosomal rRNA