Guanine is a purine base. Adenine is another purine base. Cytosine, Thymine and Uracil are pyrimidines.

Assertion :Purine bases present in DNA are adenine and guanine. Reason: The base thymine is present in RNA while base uracil is present in DNA.

Assertion :Purine bases present in DNA are adenine and guanine. Reason: The base thymine is present in RNA while base uracil is present in DNA.

Hence, purine is replaced with purine (adenine to guanine and vice versa) and pyrimidine is replaced with the pyrimidine (cytosine to thymine/uracil and vice versa) only; option A is correct. Substitution of purine base for a pyrimidine base or substitution of pyrimidine base for a purine base is called as transversion.

In case of transition, purine base is replaced by another purine base e.g. A⇌G (A=adenine, G=guanine) and pyrimidine is replaced by another pyrimidine e.g.,C⇌T (C=cytosine, T=thymine) and vice-versa.

What are the 2 purine bases and the 2 pyrimidine bases? View Solution. Q5. What are purines? View Solution ...

The transition is the substitution of one type of base by other of its own type. Hence, purine is replaced with purine (adenine to guanine and vice versa) and pyrimidine is replaced with a pyrimidine (cytosine to thymine/uracil and vice versa) only; option A is incorrect.

Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (either ribose or deoxyribose), whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and one or more phosphate groups.

Purines and pyrimidines, make up the two groups of nitrogenous base which plays on important role in structural backbone of DNA. Adenine and guanine are purines, while cytosine and thymine are pyrimidines. Purines pairs with pyrimidines, by formation of H-bonds.

ATP is known as energy currency of the cell and it is a nucleotide formed by the combination of adenine as a nitrogenous base, ribose sugar, and triphosphate. It is found in free cells which breaks to form energy by breaking its high energy phosphate bonds.