DNA replication (3.1.5.2)
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DNA replication is the process by which DNA is copied.
It follows a semi–conservative mechanism; each new DNA molecule consists of one original (parental) strand and one newly synthesised strand.
This ensures that each daughter cell receives an exact copy of the DNA, maintaining genetic continuity between generations of cells.
Watson and Crick proposed the semi–conservative model of DNA replication. This replication mechanism was validated by the Meselson–Stahl experiment (1958) using two different isotopes of nitrogen: and
DNA replication begins with DNA helicase unwinding the DNA double helix, separating the two strands by breaking the hydrogen bonds between complementary bases.
This separation creates two single–stranded templates that can both be used for synthesising new DNA strands.
Free DNA nucleotides bond to their complementary base pairs on the parent strands of DNA. DNA polymerase joins these nucleotides via condensation reactions, which form phosphodiester bonds.
Two identical daughter DNA molecules are created, each containing one parent strand and one newly synthesised strand.