Question:

In sea urchin DNA, which is double stranded, 17% of the bases were shown to be cytosine. The percentages of the other three bases expected to be present in this DNA are

Updated On: Jul 12, 2022
  • G 17%, A 33%, T 33%
  • G 8.5%, A 50%, T24.5%
  • G 34%, A 24.5%, T24.5%
  • G 17%, A 16.5%, T 32.5%.
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The Correct Option is A

Solution and Explanation

According to Chargaff's rule, the amount of adenine is always equal to that of thymine and the amount of guanine is always equal to that of cytosine. 374 i.e.y A = T and G = C. Also, the purines and pyrimidines are always in equal amounts, i.e., A + G = T + C. Now, given dsDNA has 17% cytosine and hence guanine will be also 17%. So, A + T must be 66% Therefore, percentage of adenine or thymine would be 66/2 = 33%.
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Concepts Used:

The Molecular Basis of Inheritance

DNA Replication:

DNA synthesis is commenced at particular points within the DNA strand referred to as ‘origins’, which are certain coding regions. There are numerous origin sites, and when replication of DNA starts, these sites are mentioned as replication forks. Within the replication, the complex is the enzyme DNA Helicase, so that they can be utilized as a template for replication. DNA Primase is another enzyme that's essential in DNA replication.

RNA:

Ribonucleic acid (RNA) is an essential biological macromolecule that exists all together in biological cells. It is principally involved in the synthesis of proteins, that carry the messenger instructions from DNA, which itself contains the genetic instructions needed for the event and maintenance of life. In some viruses, RNA, in spite of DNA, carries genetic information.

Genetic Code:

Genetic code is the term we use in the manner that the four bases of DNA--the A, C, G, and Ts--are strung together in a way that the ribosome, the cellular machinery, can read them and switch them into a protein. In the ordering, every three nucleotides during a row count as a triplet and code for one amino alkanoic acid.

Read More: Molecular Basis of Inheritance