Question

Boris Magasanik collected data on the proportion of each base in RNA from different species. To compare the relative amount of each base among the sources, he standardized the value of adenine to 10. Relative amounts of the other bases were calculated based on this value for adenine.
The data are shown below.

Normalized Ratio
A G C U
Organism and Tissue 10 14.8 14.7 12.0
Rat liver nuclei 10 14.3 12.0 8.0
Rabbit liver nuclei 10 12.9 9.5 9.8
Cat brain 10 13.6 21.0 14
Carp muscle 10 13.1 19.0 9.5
Yeast 10 14.0 11.0 12.9

(a) Calculate the ratio of purines to pyrimidines. Enter your answer as a decimal.
(b) For rabbit liver nuclei, calculate the ratio of purines to pyrimidines.

Answer 1

Answer:

The nucleic acid is a macromolecule present in living systems in the form of either DNA or RNA, whose molecule consists of many nucleotides which are linked with each other to form long chains. The presence of DNA or RNA in an individual promotes continuity of life. The variability and complexity of nucleic acid are dependent on its constituent molecules as, sugar, a phosphate group, and a nitrogenous base. However, two monocyclic nitrogenous bases were classified purines (adenine:A, guanine:G) and pyrimidines (thymine:T, cytosine:C, and uracil:U).

In addition, RNA is a single-stranded structure which differs from DNA in two aspects, the sugar content of RNA is ribose, and pyrimidine base uracil replaces the thymine base of DNA. A ratio between two strands of DNA can be calculated by using Chargrff's rule which states that "DNA from any cell of all organisms possess a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases'.

The purine to pyrimidine ratio in RNA with different bases is given below in the following table:

Presence of single strand in RNA does not follow chargaff's rule and alters the purine: pyrimidine ratio. The above ratio of each base in the given information is not equal, due to which the ratio of purines to pyrimidines is different. The ratio of DNA and RNA is not equal because DNA has its complementary DNA strand. However, bases in RNA might vary due to its single-strandedness property, but its ratio is dependent on the species.

Therefore, it can be concluded that the ratio of purines to pyrimidines is dependent on the species due to its genetic makeup. Hence, option (c) is correct.