Question

The genome of an organism was analyzed and provided the following: 17%A, 23%G, 32%C, 0%T, and 28%U. This organism is likely:

		A virus
		A virus or a bacterium
		A bacterium
		A bacterium or a eukaryote
		A eukaryote
		It cannot be calculated based on that number alone

Answer 1

• The bases of both RNA or DNA forms hydrogen bonds creating “base pairs”.
• According to Erwin Chargaff, these base pairing follows certain rules, designated as Chargaff rule
• The Purine base of a nucleotide, will bond with pyrimidine of the other nucleotide. . Thus making the purine content of a nucleic acid equivalent to pyrimidine content.

In DNA, base pairing between two complementary strands takes place as:

• Adenine is attached to Thymine by two hydrogen bonds (A=T).
• Guanine is attached to Cytosine by three hydrogen bonds (G=C).

RNA may form base pairing, during its folding or forming hybrid with DNA.

• Where the Adenine pairs to uracil (A=U) by two hydrogen bonds.
• The base pairing results in formation of secondary structure of nucleic acids.

• In case of single stranded RNA, Chargaff rule is not followed.
• As in the given scenario, the genome does not contain Uracil.
• Also purine content is not equivalent to pyrimidine content.
• Thus, the genome is not DNA, and does not belong to an eukaryotic organism or bacteria.
• Thus, this indicate the genome to belong to virus.

Answer: A virus