Question

Which of the following nitrogenous bases is absent in RNA?
A. Guanine
B. Adenine
C. Uracil
D. Thymine

Answer 1

RNA - Ribonucleic acid or RNA is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. Ribonucleic acid or RNA and DNA or Deoxyribonucleic acid are nucleic acids.
RNA contains four nitrogenous bases. These are adenine, cytosine, uracil and guanine. Uracil is a pyrimidine that is mechanically similar to thymine, another pyrimidine that can be found in DNA or Deoxyribonucleic acid. Such as thymine and uracil can base-pair with adenine.

Complete answer:
Adenine, guanine and cytosine are the nitrogenous bases present in both DNA and RNA. While thymine is present only in DNA or Deoxyribonucleic acid. RNA or Ribonucleic acid has uracil instead of thymine.
Guanine all the time binds with cytosine by hydrogen bond. Adenine forms a hydrogen bond with a thymine in DNA or Deoxyribonucleic acid and with a uracil in RNA or Ribonucleic acid.
So, the correct option is 'Thymine'.
Additional Information:
Option A – Guanine: We can find Guanine nitrogenous base in RNA. It can be found in DNA as well.
So, the option A ‘Guanine’ is not the correct answer.
Option B – Adenine: We can find Adenine nitrogenous base in RNA. It can be found in DNA as well.
So, the option B ‘Adenine’ is not the correct answer.
Option C – Uracil: We can find Uracil nitrogenous base in RNA, but it can’t be found in DNA.
So, the option C ‘Uracil’ is not the correct answer.

Note:
Each RNA nucleotide contains a nitrogenous base, a ribose sugar and a phosphate. About 5% of the weight of a human cell is RNA or Ribonucleic acid. Only about 1% of a cell consists of Deoxyribonucleic acid or DNA. Ribonucleic acid is used in some cancer-gene therapies to decrease the expression of cancer-causing genes.