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Question 567
Genetics → General
Classification
Question
SSBAQuestion Header
Which additional component is required to make this compound a nucleotide?
Question Stem
An adenine molecule joined to deoxyribose forms a DNA nucleoside.
Options
A
Ribose
B
Uracil
C
Phosphate
D
Cytosine
E
Guanine
Explanation
A DNA nucleotide contains a nitrogenous base, deoxyribose and phosphate. A nucleoside contains only the base and sugar. Addition of phosphate therefore supplies the component that distinguishes a nucleotide from a nucleoside.
Option Validity
A) Ribose is the sugar in RNA. The DNA nucleoside already contains deoxyribose; adding a second sugar does not supply the missing phosphate.
B) Uracil is a nitrogenous base in RNA. Adding another base does not provide the phosphate required for a nucleotide.
D) Cytosine is another nitrogenous base. The nucleoside already contains adenine and still requires phosphate.
E) Guanine is another nitrogenous base. Adding it does not supply the phosphate that distinguishes a nucleotide from a nucleoside.
Further Reading
Saxena R. Textbook for MRCOG-1: Basic Sciences in Obstetrics and Gynaecology. 1st ed. Jaypee Brothers Medical Publishers; 2016. Chapter 8: Genetics — Deoxyribonucleic Acid. Printed page 254.