Question

Molecular weight is highest of

• A. guanine
• B. thymine
• C. adenine
• D. cytosine

Answer 1

Answer: (A)

Guanine has the molecular formula $C_5{H}_5$ $N_{5}O$ with molecular weight of $151amu$. Adenine is $C_5{H}_5{N}_5$ (molecular weight $135amu$), cytosine is $C_4{H}_5{N}_{3}O$ (molecular weight $111amu$) and thymine is $C_5{H}_6{N}_2{O}_2$ (molecular weight $126amu$). Thus guanine is the heaviest nitrogenous base found in $DNA$.