Question

If a DNA double helix is 100 nucleotide pairs long and contains 25 adenine bases, how many guanine bases does it contain?

Answer 1

`25`

Explanation:

Well, we have to know the base pairs for `"DNA"` first. Adenine only bonds with thymine with two hydrogen bonds, while guanine only bonds with cytosine with three hydrogen bonds. Bonding pairs can also happen vice-versa.

Since there are `100` nucleotides in this strand and `25` adenine bases, then that must mean that there are also `25` thymine bases.

So, there are a total of `25+25=50` adenine and thymine bases in total. That leaves `100-50=50` remaining bases. Note that cytosine and guanine bond with each other, and so they are equal in amounts. We can now divide by `2` to get the number of guanine or cytosine bases.

`50/2=25`

Therefore, there are `25` guanine bases.