Semi-Conservative Replication
Definition
The mode of DNA copying in which each daughter double helix retains one parental strand and acquires one newly synthesised strand, confirmed by Meselson and Stahl in 1958 using nitrogen-15 density labelling.
- Mechanism
- Each daughter helix keeps one parental strand, one new strand
- Confirmed by
- Meselson and Stahl
- Year
- 1958
- Method used
- Nitrogen-15 density labelling
- Field
- Molecular biology underlying DNA replication
Common questions
How did the Meselson-Stahl experiment distinguish semi-conservative from other models?+
They grew bacteria in heavy nitrogen-15, then switched to normal nitrogen-14 and used density-gradient centrifugation to track DNA density over successive generations. The intermediate-density band that appeared after one replication cycle ruled out both fully conservative and fully dispersive models.
Why does semi-conservative replication matter for forensic DNA work?+
It explains why replication is high-fidelity and why errors introduced during PCR amplification, which mimics this templated copying process, can be distinguished from true biological mutations when interpreting profiles or investigating degraded samples.
What are the two other replication models that were ruled out?+
The conservative model proposed that the original double helix stays intact while an entirely new copy forms, and the dispersive model proposed that both strands of both daughter molecules contain a patchwork mix of old and new DNA.
Related terms
- DNA Polymerase
- The enzyme that synthesises new DNA by adding deoxyribonucleoside triphosphates complementary to the template strand. In humans, polymerase delta copies the lagging...
- Frameshift Mutation
- A change in the reading frame of a coding sequence caused by an insertion or deletion of a number of nucleotides that...
- Okazaki Fragment
- A short segment of DNA (100 to 200 nucleotides in eukaryotes) synthesised on the lagging template strand in the 5-prime to 3-prime...
- Point Mutation
- A change in a single nucleotide in the DNA sequence. A transition substitutes one purine for another or one pyrimidine for another...
- Short Tandem Repeat (STR) Slippage
- Replication slippage at a repetitive locus where the template and nascent strands temporarily misalign. If the nascent strand slips forward, one repeat...