Prof. Dr. Sohan Raj Tater
The cell is the fundamental structural and functional unit of all living beings (organisms). There are certain differences between the cells of different living organisms as well as the cells in the different part of the living organisms. All cells contain a fluid called cytoplasm and a nucleus and are enclosed in a cell membrane. Operations with in the cells and co-ordination among various cells make the being live. The life of all the living beings is, therefore, based upon the working of the cells.
The nucleus of a cell contain a chemical DNA (Deoxyribonucleic Acid). All the instructions needed to direct the activity of cell are contained within the DNA. DNA is a polymer. The monomer units of DNA are nucleotides and the polymer is known as a "polynucleotide". There are four different types of nucleotides found in DNA, differencing only in the nitrogenous base. The four nucleotides are:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
DNA of all the organisms is made up of the same chemical and physical components. The DNA sequence is the particular side-by-side arrangement of bases along the DNA strand.
This order spells out the exact instructions required to create a particular organisms with its own unique traits. The DNA is normally the form of a double strand (double helix). Where the second strand is complementary to the first strand. That is, in the second strand a sequence such as AGGTTT is replaced by TCGAAA which carries the same information.
Doctoral Thesis, JVBU