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Why is DNA replication called a "semi-conservative" process?
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Step 1:
I'll solve this problem step by step, explaining the semi-conservative nature of DNA replication:

Step 2:
: Understanding DNA Structure

- DNA is composed of two complementary strands that form a double helix - Each strand is made up of nucleotides with a specific base pairing (A-T, C-G) - The two strands are held together by hydrogen bonds between complementary bases

Step 3:
: Defining Semi-Conservative Replication

- In semi-conservative replication, when DNA duplicates: * Each new DNA molecule contains ONE original (parent) strand * ONE completely new (daughter) strand is synthesized - This means the original DNA "unzips", and each original strand serves as a template for a new complementary strand

Step 4:
: Mechanism of Semi-Conservative Replication

- During replication: * The double helix separates (unwinds) * Each original strand acts as a template * Complementary nucleotides are brought in to create new strands * Result: Two identical DNA molecules, each containing one original and one new strand

Step 5:
: Experimental Proof (Meselson-Stahl Experiment)

- In 1958, Matthew Meselson and Franklin Stahl definitively proved the semi-conservative model - They used nitrogen isotopes to track DNA strands during replication - Demonstrated that each new DNA molecule contains one "old" and one "new" strand

Final Answer

DNA replication is called "semi-conservative" because each newly formed DNA molecule contains one original (parent) strand and one newly synthesized (daughter) strand, preserving half of the original genetic information in each new molecule.