The nucleotide sequence of one DNA strand of a DNA double helix is 5-ʹGGATTATTGTGCACTTTCA-3ʹ. What is the sequence of the complementary strand and briefly explain the answer?

1 Answer

3'-"CCTAATAACACGTGAAAGT"-5'

Explanation:

We have directionality involved in this "DNA" sequence. If it starts with a 5' and ends in a 3', then the complementary strand will start with 3' and end with 5'.

So, the first step is to write:

3'-5'

Now, we need to note the complementary values. Adenine ("A") only bonds with thymine ("T") because both of them have place
only to form two hydrogen bonds, while cytosine ("C") only bonds with guanine ("G"), as they have three places for hydrogen bonds to form. Note that this can also happen vice-versa.

So, we just need to change letters in the complementary strands to their "partners", i.e. "A"rightleftharpoons"T" \ "and" \ "C"rightleftharpoons"G".

Our complementary "DNA" strand to this would be:

3'-"CCTAATAACACGTGAAAGT"-5'

Hope this helps!