This document discusses DNA and RNA base pairing. It explains that DNA contains the nucleotide bases adenine, thymine, guanine and cytosine, which pair in a complementary fashion with adenine binding to thymine and guanine binding to cytosine. RNA contains uracil instead of thymine. The complementary sequence to the given DNA sequence CTAATGT is determined to be GATTACA. Since thymine is present rather than uracil, it is identified as a DNA sequence rather than RNA.

1. 19. DNA “Nucleotide bases” are selective in their bonding. Thinking about your readings, and
the details discussed in lecture 2~4, what is the corresponding (“mirror image”) sequence of
bases for the DNA strand CTAATGT?
In question 19, I stated that the sequence of nucleotide bases was DNA, rather than RNA, but
you could have known this anyway, just by looking at the bases that are present. How do you
know that this was not a sequence of RNA?
Solution
Genes consist of specific sequences of DNA nucleotides (complementary base pairs) which code
for the structure of polypeptide chains. These polypeptide chains are tRNA (transfer RNA) and
mRNA (messenger RNA), which perform transcription and translation processes respectively
during protein synthesis.
So, these DNA nucleotides otherwise called “bases” carry the message encoding for the
synthesis of a protein. There are four such bases, namely, adenine (A), thymine (T), guanine (G),
and cytosine (C), which are the building blocks of DNA’s double helical structure. RNA contains
Uracil (U) in place of thymine.
Among these base pairs, adenine binds with thymine and guanine binds with cytosine, this is
called as complementary pairing. In RNA, adenine binds with uracil.
The corresponding sequence/mirror image/complimentary sequence od the given DNA sequence
CTAATGT is, GATTACA.
We can determine that the above sequence is DNA because thymine is present. RNA contains
uracil in place of thymine.