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!