If the template strand of DNA is of the sequence 5’-AGTTGC-3’, what sequence will DNA polymerase synthesise?

Question

BlackTom AI · Accepted Answer

Complementary base pairing gives the new strand sequence T C A A C G paired to the template A G T T G C, and the newly synthesized strand must be antiparallel to the template. Key points: DNA bases pair A–T and G–C; strands run with opposite polarity (5' and 3'); DNA polymerase builds the new strand antiparallel to the template.

Step-by-step reasoning:
1. Write the template 5' → 3': 5'- A  G  T  T  G  C -3'
2. For each base, write its complement (A→T, G→C, T→A, T→A, G→C, C→G):
   - A complements T
   - G complements C
   - T complements A
   - T complements A
   - G complements C
   - C complements G
   This produces the complementary series (in the opposite direction): T  C  A  A  C  G
3. Because DNA strands are antiparallel, if the template is 5'→3', the complementary strand runs 3'→5'. Writing the complementary sequence with its ends labeled gives 3'- T  C  A  A  C  G -5'.

Why this is correct: option (a) exactly matches the complementary bases and the antiparallel orientation: 3’-TCAACG-5’. Note on polymerase direction: DNA polymerase synthesizes in the 5'→3' direction relative to the new strand, so if you prefer to write the newly made strand 5'→3' you would reverse option (a) to 5'-GCAACT-3'; however that reversed form is not one of the answer choices. Option (a) is the complementary sequence shown in the antiparallel orientation that matches the template as given.

Why the other answers are incorrect:
- (b) 5’-AGTTGC-3’ is just the original template, not the complement.
- (c) 5’-TCAACG-3’ has the correct base sequence but the wrong orientation (it should be 3'→5' relative to the template as given).
- (d) 3’-AGTTGC-5’ is the template flipped, not the complementary sequence.

Confirming final answer: the correct choice is a. 3’-TCAACG-5’.

If the template strand of DNA is of the sequence 5’-AGTTGC-3’, what sequence will DNA polymerase synthesise?单项选择题

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