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 Transcription:
Transcription is the process of creating an mRNA molecule from a DNA template. The DNA template strand is read from 3' to 5', producing a complementary mRNA strand in the 5' to 3' direction. Base pairing rules are: DNA Adenine (A) pairs with RNA Uracil (U), DNA Thymine (T) pairs with RNA Adenine (A), DNA Guanine (G) pairs with RNA Cytosine (C), and DNA Cytosine (C) pairs with RNA Guanine (G).

Step 2: Determining the Template DNA Sequence:
1. Identify the mRNA sequence:
The provided mRNA sequence is 5'-CAUUGGCCAAGG-3'.
2. Determine the complementary DNA template:
To determine the template DNA strand, apply the base-pairing rules (A-T, G-C, U-A) to the mRNA sequence.
\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. Convert to standard 5' to 3' direction:
DNA sequences are conventionally written 5' to 3'. Reverse the 3' to 5' sequence from the previous step.
The sequence 3'-GTAACCGGTTCC-5' becomes 5'-CCTTGGCCAATG-3'.

Step 3: Analysis of Options:
Comparing the derived sequence to the options: Option (B) matches the correct 5'-CCTTGGCCAATG-3' sequence. Option (A) represents the coding strand (T instead of U). Option (C) is the template strand in the incorrect 3' to 5' orientation. Option (D) is the original mRNA sequence.