Question

during dna replication, a dna double-helix is unwound before it is copied. after this, what is used as a template for dna synthesis? select the one best answer.
one of the dna strands from the unwound double-helix
both of the dna strands from the unwound double-helix
only the non-template (coding) strand from the un-wound double-helix
only the template strand from the un-wound double helix

incorrect
recall that dna replication starts with a double-helix and ends with two double-helices. if only one strand from the un-wound double-helix was used as a template, dna replication would end with one new double-helix and an unpaired, single-stranded dna molecule.

Explanation:

DNA replication is semi - conservative. The double - helix unwinds, and each strand (both the template and non - template/coding strands) serves as a template. New complementary strands are synthesized based on the base - pairing rules (A - T, G - C). If only one strand was used as a template, we would not get two double - helices at the end of replication as per the semi - conservative model.

Answer:

both of the DNA strands from the unwound double - helix