Question

The fusogen used during the protoplast fusion is known as
A. PEG
B. Magnesium chloride
C. Calcium phosphate
D. All of the above

Answer 1

Purines are the building blocks of the DNA fragments and the binding occurs complementarity to the purines. There exist only two different purines. Use Chargaff’s Rule to know about the binding and then identify the purines and pyrimidines from all the available bases and then solve the question.

Complete answer:
We all know that DNA is a double stranded fragment and the two different fragments of DNA are joined together with the help of the Hydrogen bonds which are formed between the nucleotide bases present in the DNA fragments. Now if seen, these nucleotide bases are present complementarily to each other and they cannot form hydrogen bonds with their same type. Nucleotides bases are of two types which are Purines and pyrimidines. So, in a DNA fragment the purine will bind to pyrimidine only and vice-versa. This was observed by Irwin Chargaff and thus the rule was given known as Chargaff’s rule.
In DNA there are a total of four purines and pyrimidines are present out of which two are purine and two are pyrimidines. The purine present in the DNA are Adenine(A) and Guanine(G) and the pyrimidines are Thymine(T) and Cytosine(C). According to Chargaff’s Rule, A binds with T and they both are complementary to each while G binds with C and they are also complementary to each other.

So, from the above made discussion we can say that the A and G are the purines present in the DNA, and thus option B is correct.

Note: DNA is a double stranded molecule having A-T and G-C bonds but if we see RNA molecule which is single stranded, the bindings method remains the same but in the place of Cytosine the RNA molecule have a different pyrimidine named Uracil and it is complementary to the Guanine.