the following diagram shows a double - stranded dna molecule.
which of the following represents the correct mrna molecule that will result from the transcription of the dna molecule?
choose 1 answer:
a
5 a g u c u a c g 3
b
5 u c a g a u g c 3
c
5 c g u a g a c u 3
d
5 g c a u c u g a 3

Question

Accepted Answer

To solve this, we analyze DNA transcription:

### Step 1: Identify the template strand
Transcription uses the **non - coding (template) strand** of DNA. The coding strand has the same sequence as mRNA (except T→U), but transcription is from the non - coding strand. From the diagram, the non - coding strand (right) has the sequence (from 3’ to 5’): $ 3' - C\ G\ T\ A\ G\ A\ C\ T - 5' $ (wait, no—let's read the non - coding strand correctly. Wait, the DNA is double - stranded: coding strand (left) is $ 3' - G\ C\ A\ T\ C\ T\ G\ A - 5' $? Wait, no, let's look at the base pairs. The coding strand (left) has bases (top to bottom): G, C, A, T, C, T, G, A (from 3’ to 5’? Wait, the coding strand is labeled 3’ at top, 5’ at bottom. So coding strand sequence (3’→5’): G - C - A - T - C - T - G - A. The non - coding (template) strand is complementary: C - G - T - A - G - A - C - T (3’→5’? Wait, no, DNA strands are antiparallel. The coding strand is 3’ top, 5’ bottom; non - coding is 5’ top, 3’ bottom? Wait, the diagram shows coding strand with 3’ at top, 5’ at bottom; non - coding with 5’ at top, 3’ at bottom (since the ends are labeled 5’ and 3’). So non - coding strand (template) sequence (5’→3’): C - G - T - A - G - A - C - T? No, let's list the base pairs:

Coding strand (left, 3’→5’): G (3’), C, A, T, C, T, G, A (5’).
Non - coding (right, 5’→3’): C (5’), G, T, A, G, A, C, T (3’). Wait, no—each base pair: G - C, C - G, A - T, T - A, C - G, T - A, G - C, A - T. So coding strand (3’→5’): G C A T C T G A. Non - coding (template) strand (5’→3’): C G T A G A C T.

### Step 2: Transcribe template to mRNA
Transcription: mRNA is synthesized 5’→3’, complementary to the template strand (DNA→RNA: A→U, T→A, C→G, G→C). The template strand is read 3’→5’ (since DNA is antiparallel, and mRNA is synthesized 5’→3’). Wait, the template strand (non - coding) is 5’→3’? No, DNA template is read 3’→5’ by RNA polymerase, and mRNA is made 5’→3’. So we need to reverse the template strand to read it 3’→5’, then transcribe.

Wait, let's correct: The coding strand is identical to mRNA (except T→U) because the coding strand has the "code" for the protein. Wait, actually, the **coding strand** has the same sequence as the mRNA (with T instead of U). So if the coding strand is $ 3' - G\ C\ A\ T\ C\ T\ G\ A - 5' $ (wait, no—coding strand is 3’ at top, 5’ at bottom. So the coding strand sequence (from 3’ to 5’): G (3’), C, A, T, C, T, G, A (5’). So the mRNA, being complementary to the template (non - coding) strand, will have the same sequence as the coding strand, with T replaced by U. So coding strand: $ 3' - G\ C\ A\ T\ C\ T\ G\ A - 5' $ → mRNA (5’→3’) should be $ 5' - G\ C\ A\ U\ C\ U\ G\ A - 3' $? Wait, no—wait, the coding strand is 3’ at top, 5’ at bottom. So the coding strand sequence (5’→3’) would be the reverse: A (5’), G, T, C, T, A, C, G (3’)? No, I think I messed up the direction. Let's start over.

DNA strands are antiparallel. The coding strand (sense strand) has the same sequence as mRNA (T→U). The template strand (antisense) is complementary. Let's list the coding strand (left) bases from top (3’) to bottom (5’): G, C, A, T, C, T, G, A. So coding strand sequence (3’→5’): G - C - A - T - C - T - G - A. Therefore, the mRNA, which is synthesized 5’→3’, will have the same sequence as the coding strand but with T→U, and in the 5’→3’ direction (so reverse the coding strand’s 3’→5’ to 5’→3’). Wait, no—if the coding strand is 3’→5’ as G C A T C T G A, then the 5’→3’ of coding strand is A G T C T A C G. Then mRNA (5’→3’) would be A G U C U A C G (since T→U). Wait, option A is $ 5' - A\ G\ U\ C\ U\ A\ C\ G - 3' $. Let's check:

Coding strand (5’→3’): A (5’), G, T, C, T, A, C, G (3’). Transcription: mRNA is complementary to template (non - coding) strand, but the coding strand is same as mRNA (T→U). So coding strand 5’→3’: A - G - T - C - T - A - C - G. mRNA (5’→3’): A - G - U - C - U - A - C - G. Which matches option A.

# Answer: A. $ 5' - A\ G\ U\ C\ U\ A\ C\ G - 3' $

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QUESTION IMAGE

Question

Explanation:

Step 1: Identify the template strand

Step 2: Transcribe template to mRNA

Answer: