Cydney T. answered • 06/08/20
Experienced, patient, knowledgeable tutor!
The nitrogenous bases are Adenine (A), Guanine (G), Thymine (T), Cytosine (C), and Uracil (U). A pairs with T in DNA and with U in RNA. C always pairs with G. This question is tricky because not only does it want you to find the complementary strand, but it wants you to find the complementary MRNA strand when it gives you a DNA strand. So let's break it up.
When you go from DNA to RNA, all of the Thymines turn into Uracils.
When you look at a strand of DNA or RNA, you can figure out what the complementary strand is by writing the match to each base on the parent strand (which is the strand you were given). So, if your strand of DNA gave you a C, you know it will be matched to a G on the complementary strand.
Let's start with the complementary strand for the DNA strand you were given first. We know A matches with T, and G matches with C. So your DNA strand would be TTT/AAA/CCC/GGG. But we aren't done yet, because we need to find what this strand is in MRNA. To do this, we need to change all of the Thymines to Uracil. So, your strand would actually be UUU/AAA/CCC/GGG.
I hope this helps!
Bruce P.
Be careful here; formally DNA and RNA should always be written in the 5' -> 3' direction, and if no notation is used, the left is the 5' end. So the complementary strand would have its 5' end to the right and should either be written as 3' -UUUAAACCCGGG-5' (using the notation to indicate orientation) or GGGCCCAAAUUU using the convention of 5' assumed to be on the left A lot of teachers use this as a trick question; I encourage students to always write the lower strand upside down as a reminder that it is oppositely oriented.06/13/20