Question

Which nitrogen base is absent in DNA?
A) Adenine
B) Guanine
C) Uracil
D) Cytosine

Answer 1

‌DNA (deoxyribonucleic acid) is a linear molecule which is made up of four chemical molecules called nucleotide bases. It consists of two polynucleotide chains coiled around each other in a double helix structure carrying genetic information.

Complete answer:
DNA (deoxyribonucleic acid) is a biological molecule that encodes all genetic information and acts as a genetic blueprint. They carry all the genetic information related to a living thing including development, growth, functioning and reproduction. DNA (deoxyribonucleic acid) is a double stranded structure where these strands are called polynucleotides and it is made up of small monomeric units called nucleotides. Each of this nucleotide is made up of four nitrogen-containing nucleobases (cytosine, thymine, adenine, guanine) a sugar molecule called deoxyribose and a phosphate group.
Hence the nitrogen base absent in DNA (deoxyribonucleic acid) is uracil
Therefore the correct option is option C..

Additional Information: It is by means of a covalent bond between the sugar of one nucleotide and the phosphate of the other creating alternate sugar phosphate backbone the nucleotides are joined with one another. The nitrogen bases present in the two polynucleotide strands are held together by some base pairing rules (i.e. Adenine with Thymine and Cytosine with Guanine) with hydrogen bond to make double-stranded DNA. There are two groups of nitrogen bases pyrimidines and purines. The biological information stored in the two strands will be the same. When the two strands are separate the information gets replicated. The strands of DNA run in the opposite direction to each other and they are anti parallel.

Note: DNA (deoxyribonucleic acid) is a long polymer made up of small repeating units called nucleotides. DNA (deoxyribonucleic acid) has dynamic structure along its length and is capable of coiling into tight loops and other shapes.