What does semi-conservative replication mean in DNA replication?

What does semi-conservative replication mean in DNA replication?

• A. Each new DNA molecule has one old strand and one new strand
• B. Each new DNA molecule has two newly synthesized strands
• C. DNA replication produces only RNA primers
• D. Replication results in two identical old double helices

Answer: (A)

Semi-conservative replication means that after replication, each new DNA molecule contains one strand that came from the original molecule and one newly synthesized strand. The two strands of the original double helix separate, and each serves as a template for building a complementary new strand. Base-pairing rules ensure the new strand matches the old one, and DNA polymerases synthesize in the 5' to 3' direction to create two daughter molecules that retain one old strand and one new strand each. This preserves genetic information while allowing accurate transmission to daughter cells. Having both strands newly synthesized would imply no old material is retained, which isn’t what happens. RNA primers are only short starting sequences for synthesis, not the finished DNA, so replication products aren’t composed of RNA. And producing two identical old double helices would mean no new DNA is formed, which isn’t the case in replication.

Semi-conservative replication means that after replication, each new DNA molecule contains one strand that came from the original molecule and one newly synthesized strand. The two strands of the original double helix separate, and each serves as a template for building a complementary new strand. Base-pairing rules ensure the new strand matches the old one, and DNA polymerases synthesize in the 5' to 3' direction to create two daughter molecules that retain one old strand and one new strand each. This preserves genetic information while allowing accurate transmission to daughter cells.

Having both strands newly synthesized would imply no old material is retained, which isn’t what happens. RNA primers are only short starting sequences for synthesis, not the finished DNA, so replication products aren’t composed of RNA. And producing two identical old double helices would mean no new DNA is formed, which isn’t the case in replication.