I started learning molecular biology this semester! And, I'm very happy about it. As I love Cell and micro biology, I started loving molecular biology too. :)
My very first beginning with molecular biology is DNA. We all know very well about the structure of DNA as proposed by Watson, Crick, Rosalind Franklin & Maurice Wilkins.
1) DNA is Double stranded and acidic. They have four nitrogenous bases ATGC (Adenine, Thymine, Guanine, Cytosine), Deoxy Ribose, Phosphate. A&G are purines. C&G are pyrimidines.
2) The acidic charge is due to the phosphate group which is protruding out of the DNA.
3) A always basepairs with T & C with G. Between A&T there is a double bond of hydrogen. And, triple hydrogen bond between C and G.
i.e., Purine basepairs with pyrimidine or the viceversa.
But, why not a purine and purine, a pyrimidine and pyrimidine?
Mm... Why not??!
It won't. Because, when a purine and purine base pairs that region would be somewhat wide, due to the bulkiness of purines.
If pyrimidine and pyrimidine, that region would be so narrow. Imagine, this will lead to an irregularity in the DNA's structure. It will appear something like this. (Bulky and narrow, bulky and narrow.)
:D :D See how beautiful this irregular DNA is??? :) :)
This won't be stable.
You know, when DNA is unwound, it will stretch into kms???!!!
Shh.... Don't reveal this secret to anyone. (DNA- Secret of Life) :P :P :)
Happy learning..! Bye. Bye.