Question

What is the sequence of the template DNA for an mRNA with the sequence?
5'-CAUUGGCCAAGG-3'

• A. 5'-CATTGGCCAAGG-3'
• B. 5'-CCTTGGCCAATG-3'
• C. 5'-GTAACCGGTTCC-3'
• D. 5'-CAUUGGCCAAGG-3'

Hint:

To quickly find the template DNA strand (in 5' to 3' format) from an mRNA sequence, first find the sequence of the coding strand by replacing U with T in the mRNA sequence. Then, find the complementary sequence of the coding strand. For example, mRNA is 5'-CAUUGGCCAAGG-3'. The coding strand is 5'-CATTGGCCAAGG-3'. The complementary (template) strand is 5'-CCTTGGCCAATG-3'.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The process of creating an mRNA molecule from a DNA template is called transcription. During transcription, the DNA template strand is read in the 3' to 5' direction to synthesize a complementary mRNA strand in the 5' to 3' direction. The base pairing rules are: Adenine (A) in DNA pairs with Uracil (U) in RNA, Thymine (T) in DNA pairs with Adenine (A) in RNA, Guanine (G) in DNA pairs with Cytosine (C) in RNA, and Cytosine (C) in DNA pairs with Guanine (G) in RNA.

Step 2: Detailed Explanation:
1. Identify the given mRNA sequence:
The given mRNA sequence is 5'-CAUUGGCCAAGG-3'.
2. Determine the complementary DNA sequence:
To find the template DNA strand, we need to write the complementary base sequence according to the base-pairing rules (A-T, G-C, and U in mRNA pairs with A in DNA).
\begin{tabular}{l c c c c c c c c c c c c} mRNA: & 5' - & C & A & U & U & G & G & C & C & A & A & G & G & - 3'
& & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) &
Template DNA: & 3' - & G & T & A & A & C & C & G & G & T & T & C & C & - 5'
\end{tabular}
3. Write the template DNA sequence in the standard 5' to 3' direction:
By convention, DNA sequences are written in the 5' to 3' direction. To do this, we read the sequence obtained in the previous step from right to left.
The sequence is 3'-GTAACCGGTTCC-5'.
Written in the 5' to 3' direction, it becomes 5'-CCTTGGCCAATG-3'.

Step 3: Final Answer:
Comparing this result with the given options, we find that option (B) matches our derived sequence. Option (A) represents the coding (sense) strand, where T replaces U. Option (C) represents the template strand but written in the incorrect 3' to 5' direction. Option (D) is the mRNA sequence itself.