Question

Nucleotides are building blocks of nucleic acids. Each nucleotide is a composite molecule formed by
A. Base-Sugar - OH
B. Base-Sugar-phosphate
C. Sugar-phosphate
D. $(Base-sugar-phosphate)_n$

Answer 1

Nucleotides are the organic molecules which consist of a nucleoside and a phosphate. They serve as the monomers or subunits of nucleic acids which are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) and both of these are essential within all the life forms on the Earth.

Complete answer:
Nucleotides are composed of three subunit molecules:
- Nitrogenous base: There are 4 nitrogenous bases present in the DNA which are guanine, adenine, cytosine and thymine but in the RNA, instead of thymine there is presence of uracil.
- Sugar (a five carbon sugar) : like Ribose or deoxyribose.
- Phosphate group: It consists of one to three phosphates.

Nucleotides function in metabolism at a fundamental and cellular level which provide chemical energy in the form of nucleosides triphosphates which are ATP, GTP, CTP, UTP and these demand energy for many cellular functions.

Now if we look at the given options,

Option A is Base-Sugar-OH, this option is incorrect since it is composed of Base, sugar and the phosphate group not OH group. Therefore, this option gets eliminated and it is the incorrect one.

Option B is Base-Sugar-phosphate. This option is correct since nucleotides are composed of base, sugar and phosphate. This option is therefore the correct one.

Option C is Sugar-phosphate. This option is incorrect as they are composed of base also not only sugar and phosphate.

Option D is (Base-sugar-phosphate)n, the numbers are fixed as there is presence of 5 carbon sugar, 4 nitrogenous bases and 1-3 phosphate groups. So, this option is the incorrect one.

Hence, the correct answer is option (B).

Note: Nucleotides are composed of four nitrogenous bases, a five carbon sugar like ribose or deoxyribose and a phosphate group with one to three phosphates. Each nucleotide is a composite of base-sugar-phosphate. In experimental biochemistry, nucleotides can be radiolabeled with radionuclides to yield radionucleotides.