Video Transcript
A section of DNA contains the order
of bases ATGCTTAA. What would the complementary
sequence of bases be? (A) ATCCAATT, (B) TACCAATT, (C)
TACGAATT, (D) TACGGATT, or (E) TTCGAATT.
DNA is a nucleic acid that stores
the genetic information needed for life. It’s responsible for all of our
different characteristics, such as the color of our eyes or how tall we are. It’s made up of two strands of DNA
that are twisted around each other to make a double-helix shape as shown here.
Let’s untwist this DNA helix shape
so we can talk more about its components. The black line is the backbone of
these DNA strands and is called the sugar–phosphate backbone. It’s made up of phosphate groups
and deoxyribose sugars. And in between these two strands
are these different-colored boxes. These are called nitrogenous bases,
or just bases for short. There are four different types of
nitrogenous bases: guanine, or G for short, represented in orange; cytosine,
represented in blue; adenine, represented in green; and thymine, represented in
pink. These individual bases often come
in pairs as you may have noticed.
You can see all the guanines
indicated here, which are always paired with a cytosine, indicated here, whereas
adenine always pairs with thymine. This isn’t a coincidence. These specific bases pair with one
another because they have an affinity for each other. This is due to hydrogen bonding
between these bases. We call two bases that pair
together complementary. And DNA bases can pair according to
certain rules, where G always pairs with C and A always pairs with T. So, when we have a sequence of
these bases, like the one that’s given in the question, all we have to do is match
these up. So guanine will pair with cytosine,
and cytosine will pair with guanine. Adenine will pair with thymine, and
thymine will pair with adenine, which now gives us our complementary sequence of
bases. Therefore, the correct answer is
TACGAATT.
