Question

What would be the nitrogen base sequences in the m-RNA formed by the given DNA segment.
3' ATGCAGCATGACCGA 5'
5' TACGTCGTACTGGCT 3'

• A. 3' UACGUCGUACUGGCU 5'
• B. 5' AUGCAGCAUGACCGA 3'
• C. 5' UACGUCGUACUGGCU 3'
• D. 3' AUGCAGCAUGACCGA 5'

Hint:

The mRNA sequence is identical to the coding strand (5' to 3' DNA strand), with the sole exception that Thymine (T) is replaced by Uracil (U).
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Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks us to determine the nucleotide sequence of the mRNA molecule transcribed from a double-stranded DNA segment with known sequences and polarities.

Step 2: Key Formula or Approach:
1. Transcription is catalyzed by RNA polymerase, which reads the template DNA strand in the 3' to 5' direction.
2. The synthesized mRNA strand is complementary and antiparallel to the template strand, growing in the 5' to 3' direction.
3. In RNA, Uracil (U) replaces Thymine (T) as the complementary base for Adenine (A).

Step 3: Detailed Explanation:

• Identify the template strand: The template strand must have 3' to 5' polarity.
From the given DNA: \[ \text{Template Strand:} \quad 3' \text{ ATGCAGCATGACCGA } 5' \]

• Synthesize the complementary RNA strand in the 5' to 3' direction using complementary base pairing rules: \[\begin{aligned} 3' \text{ A} &\rightarrow 5' \text{ U} \\ \text{T} &\rightarrow \text{ A} \\ \text{G} &\rightarrow \text{ C} \\ \text{C} &\rightarrow \text{ G} \\ \text{A} &\rightarrow \text{ U} \\ \text{G} &\rightarrow \text{ C} \\ \text{C} &\rightarrow \text{ G} \\ \text{A} &\rightarrow \text{ U} \\ \text{T} &\rightarrow \text{ A} \\ \text{G} &\rightarrow \text{ C} \\ \text{A} &\rightarrow \text{ U} \\ \text{C} &\rightarrow \text{ G} \\ \text{C} &\rightarrow \text{ G} \\ \text{G} &\rightarrow \text{ C} \\ \text{A} &\rightarrow \text{ U } 3' \end{aligned}\]

• Writing this sequence from 5' to 3' gives: \[ 5' \text{ UACGUCGUACUGGCU } 3' \]

Step 4: Final Answer:
The resulting mRNA sequence is 5' UACGUCGUACUGGCU 3'.