Question

Length of the DNA is 1700Å.The number of nucleotides it contains is
A. 1000
B. 500
C. 3400
D. 850

Answer 1

Hint: The basic construction block of nucleic acids is a nucleotide. RNA and DNA are polymers which are made of long nucleotide chains. A nucleotide consists of a sugar molecule bound to a phosphate group and a nitrogen-containing base (either ribose in RNA or deoxyribose in DNA).

Complete Answer:
Three subunit molecules are composed of nucleotides: a nitrogen base (also known as nucleobase), a five-carbon sugar (ribose or deoxyribose) and a group of phosphates consisting of one to three phosphates. Guanine, adenine, cytosine and thymine are the four nitrogenous bases in DNA; uracil is used instead of thymine in RNA.

At a basic, cellular level, nucleotides also play a central role in metabolism. In the form of nucleoside triphosphates, adenosine triphosphate (ATP), guanosine triphosphate (GTP), cytidine triphosphate (CTP) and uridine triphosphate (UTP), they provide chemical energy throughout the cell for the many cellular functions that require energy, including: synthesis of amino acid, protein and cell membrane, movement of cell and cell parts (both internally and intracellularly), cellular functions.

Nucleotides can be synthesised both in vitro and in vivo by a number of means.In vitro, protective groups can be used during nucleotide development in the laboratory. To produce a phosphoramidite, a purified nucleoside is covered, which can then be used to acquire analogues not present in nature and/or to synthesise an oligonucleotide.

In vivo, or recycled through salvage pathways, nucleotides can be synthesised de novo. The components used in de novo nucleotide synthesis are derived from carbohydrate and amino acid metabolism biosynthetic precursors and from ammonia and carbon dioxide. The liver of all four nucleotides is the main organ of de novo synthesis.

A base pair is two chemical bases that form a "rung of the DNA ladder" bound to each other. The DNA molecule consists of two strands that wind like a twisted ladder around each other. There is a backbone made of alternating sugar (deoxyribose) and phosphate groups in each strand. Each sugar is bound to one of four bases: adenine (A), cytosine(C), guanine(G), or thymine(T). Hydrogen bonds between the bases keep the two strands together, with adenine forming a base pair with thymine and cytosine forming a base pair with guanine.
3.4 Å is occupied by every base pair (2 nucleotides).
Therefore, 1700/3.4 = 500 base pairs or 1000 nucleotides occur in a DNA segment with a length of 1700 Å.

The correct Answer is option (A)1000.

Note: At a basic, cellular level, nucleotides also play a central role in metabolism. For the many cellular functions that require it, they provide chemical energy. For living organisms, nucleotides are of considerable significance, since they are the building blocks of nucleic acids, the substances that regulate all inherited features.