which of the following composition contains ssDNA?Give reasons?

Question

a.Adenine 38%-cytosine 12%--Guanine-12%--Uracil 38%
b.Adenine 22%-cytosine 32%--Guanine-17%--Uracil 29%
c.Adenine 22%-cytosine 32%--Guanine-17%--Thymine 29%
d.Adenine 38%-cytosine 12%--Guanine-12%--Thymine 38%
e.None of the above, as this methodology will not solve the matter..

Answer 1

e.
DNA doesn't contain Uracil, RNA does so a and b can't be right. There's no way to tell the percentages of the different bases. Different organisms contain different compositions. Some are gc rich (contain more guanines and cytosines), and some are more at rich (contain large stretches or more adenine and thymine). You can't tell the composition of a single stranded DNA molecule because it isn't base paired. So the percentages above don't matter. If you have 38% adenine in a single stranded DNA molecule, you have to have 38% on the other strand that it's based paired to (synthesized from), but this isn't the case in single stranded DNA. There's no way to tell what the percentages are without more info. Either c or d could be ssDNA, but they don't have to be. A ssDNA molecule can have any percentages of A, C, T and G bases.

Answer 2

.

(a) and (b) have uracil so anyway they refer to RNA and not DNA.

In a double stranded DNA molecule each A will have a complementary T and each G will have a complementary C.
Thus A%=T% and G%=C%.

In (c) A%
However this method is not exactly correct since you can have ssDNA with A%=T% and G%=C%. So it cannot always discriminate between dsDNA and ssDNA.

Thus (e) is the more correct answer.

Answer 3

e, a and b are mRNA, thus them not qualifying as DNA. c and d are DNA however you don't know if it's single stranded. ssDNA is usually has proteins that prevent them from folding back. You don't get ssDNA easily, they fold back into a double strand, it is energetically more favorable than ssDNA due various reasons, such as entropy and bulk water. Thus my answer being e

Answer 4

C

the A's and T's don't match, neither do the Cs and G's, therefore no complimenting strand