Semi-Conservative DNA Replication

Steps:

• Helicase unwinds the double helix, separating strands at the replication fork.
• Each parental strand serves as a template for DNA polymerase to synthesize a complementary new strand.
• Synthesis occurs in 5' to 3' direction, with leading strand continuous and lagging strand in Okazaki fragments.
• Each daughter DNA has one parental and one new strand, preserving semi-conservative nature.

Why D is correct:

• Diagram D shows each unwound parental strand templating a new complementary strand, aligning with Watson-Crick base-pairing rules in semi-conservative replication.

Why the others are wrong:

• A depicts both new strands forming together, resembling conservative replication where parental strands remain intact.
• B illustrates random mixing of segments, matching dispersive model, not semi-conservative.
• C shows only one strand replicating, ignoring bidirectional template use.

Final answer: D