Question

Five samples of nucleic acids were analyzed for base composition with the following results. Which one was most probably a single stranded DNA sample?

a. 23%=A. 23%=T, 27%=C, and 27%=G.
d. 22%=A, 29%=U, 24%=C, and 25%=G.
b. 15%=A, 15%=C, 34%=G, and 369%=U.
e. 13%=A, 21%=G, 36%=T, and 30%=C.
c. 19%=A, 31%=C, 31%=G, and 19%=U.

Answer 1

The most probable single-stranded DNA sample is represented by option e. 13%=A, 21%=G, 36%=T, and 30%=C.

Step-by-step explanation:

In DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). The base composition of a DNA sample should reflect these pairing rules. Looking at option e, the percentages are 13% A, 21% G, 36% T, and 30% C. The complementary bases are A-T and G-C, and the percentages are consistent with the expected base-pairing rules of DNA.

In a single-stranded DNA molecule, the percentages of adenine and thymine (A and T) should be roughly equal, as should the percentages of guanine and cytosine (G and C). The given percentages in option e are reasonably balanced, supporting the idea that it is a single-stranded DNA sample.

Moreover, the absence of uracil (U), which is present in RNA but not in DNA, is another indication that this is a DNA sample. Options b and d include uracil (U) and are therefore more likely to represent RNA samples. Options a and c have imbalances in the percentages of A, T, G, and C, making them less likely to be single-stranded DNA. Overall, option e is the most consistent with the characteristics expected for a single-stranded DNA sample.