DNA Replication is a Semi-Conservative Process
Definition
Semi-conservative replication
When each new DNA molecule consists of one original (parental) strand and one newly synthesized strand.
- When DNA replicates, the two strands of the double helix separate.
- Each original strand serves as a template for a new complementary strand, which results in two identical DNA molecules, each containing one old strand and one new strand.
- This method ensures that genetic information is preserved with high fidelity during cell division.
- "Parents share, kids pair."
- Each parent strand is shared with a new complementary strand in the daughter molecules.
How Complementary Base Pairing Ensures High Accuracy
- Template-Driven Synthesis
- DNA polymerase reads the template strand.
- For each base on the template, DNA polymerase adds the complementary nucleotide to the new strand.
- Hydrogen Bonding as a Quality Check
- Correct base pairs form stable hydrogen bonds (A-T or C-G).
- Incorrect base pairs (e.g., A-C) do not form proper hydrogen bonds.
- If hydrogen bonding is weak or absent, the incorrect nucleotide is rejected.
- Proofreading by DNA Polymerase
- DNA polymerase has a proofreading function.
- If an incorrect nucleotide is added, DNA polymerase detects the mismatch.
- The enzyme removes the incorrect nucleotide and replaces it with the correct one.
- This dramatically reduces replication errors.
If the template has adenine (A), DNA polymerase adds thymine (T) to the new strand.
Note- This results in a very high fidelity process where the combination of complementary base pairing and proofreading ensures DNA replication is extremely accurate.
- In fact, the error rate is approximately 1 mistake per 1 billion nucleotides after proofreading.
- What does "semi-conservative" mean in the context of DNA replication?
- Describe the structure of DNA after one round of semi-conservative replication.
- What are the complementary base pairing rules?
- How does complementary base pairing ensure accurate DNA replication?
- What is the role of DNA polymerase's proofreading function?
- What would happen if complementary base pairing did not occur accurately?
