A viral DNA is analyzed and found to have the following base composition, in mole percent: A = 32, G = 16, T = 40, C = 12. What can you immediately conclude about this DNA?

a stretch of double stranded DNA contains 1000 base pairs and its base composition is 58 % (G + C). How many thymine residues are in this region of DNA?

Would you get the amount of G + C = 580, so then A + T would be 420? Then would you divide that by 2 to get the individual number of each base? So 210 thymine residues?

Tsk Tsk Tsk, Dr. M would be displeased.

To answer the question about the viral DNA's base composition, you can conclude that it is a double-stranded DNA molecule because the percentages given for each base (A, G, T, and C) add up to 100%. However, without further information, it is difficult to make additional conclusions about the DNA.

Now, to answer your question about the second scenario, you are on the right track. Since the base composition is stated as 58% (G + C), you correctly calculate that G + C = 580, indicating that the combined number of guanine (G) and cytosine (C) residues is 580.

To determine the number of thymine (T) residues in the DNA, you can calculate the combined number of adenine (A) and thymine (T) residues, as follows:

A + T = 100% - (G + C)
= 100% - 58%
= 42%

Therefore, the combined number of A + T is 42% of the total number of base pairs (1000 base pairs). To get the individual number of each base, you divide this by 2:

(A + T) / 2 = (42% / 2) × 1000
= 21% × 1000
= 210 base pairs (thymine residues)

So, you are correct that there would be 210 thymine residues in this region of the DNA.