With the exception of a few viruses, DNA forms the genetic material in all living organisms. In the prokaryotic cells DNA occurs in the cytoplasm. In the eukaryotic cells it is confined largely to the nucleus and forms the main component of chromosomes. A small amount of DNA is found in the cytoplasm in the organelles like mitochondria and plastids. It is called extra- nuclear DNA.
DNA is a polynucleotide of adenine, guanine, cytosine and thymine. Uracil nucleotides are absent. The DNA molecule is composed of two polynucleotide chains.
The structure of the DNA molecule and the arrangement of nitrogenous bases in the two polynucleotide chains, is very well explained by the double helix model proposed by Watson and Crick in 1953.
Watson and Crick
Read More
Glycolysis
The name organic chemistry came from the word organism. Prior to 1828, all organic compounds had been obtained from organisms or their remains. The scientific philosophy back then was that the synthesis of organic compounds could only be produced within living matter while inorganic compounds were synthesized from non-living matter. A theory known as “Vitalism” stated that a “vital force” from living organisms was necessary to make an organic compound. 1828, a German chemist Friedrich Wöhler (1800-1882) amazed the sience community by using the inorganic compound ammonium cyanate, NH4OCN to synthesize urea, H2NCONH2, an organic substance found in the urine of many animals. This led to the disappearance of the “Vitalism” theory.
