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DNA Replication

How a cell copies 3 billion base pairs perfectly — every single time it divides.

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DNA replication is the process by which a cell copies its entire genome before dividing — creating two identical daughter cells, each with a complete copy of the 3.2 billion base pairs of human DNA. The process is remarkably accurate: DNA polymerase makes an error once every 100,000 bases, and proofreading mechanisms correct most of these, resulting in a final error rate of about 1 per billion bases. The double helix 'unzips' at multiple origins of replication simultaneously — if replication started from just one end of a human chromosome and proceeded at the enzyme's speed, it would take 8 years to replicate one chromosome. By starting at ~30,000 origins simultaneously, replication takes 6-8 hours. DNA polymerase can add 1,000 nucleotides per second. Cancer arises when replication errors accumulate and escape correction — triggering uncontrolled cell division.

# Top 10 DNA replication facts

  1. 13.2B base pairs copied
  2. 2error rate 1/billion bases
  3. 3multiple replication origins
  4. 46-8 hours for human genome
  5. 5telomere shortening with age
  6. 6helicase unzips double helix
  7. 7lagging strand synthesized in fragments (Okazaki fragments)
  8. 8topoisomerase prevents tangling
  9. 9DNA polymerase proofreading
  10. 10cancer as replication failure

Fascinating Facts

  • ◆Your body replicates 3.2 billion base pairs of DNA in every cell division — at an error rate of 1 mistake per billion bases, meaning each new cell has about 3 errors in its 3.2 billion base pairs
  • ◆During DNA replication, the double helix must be unwound and re-wound — without the enzyme topoisomerase managing this, the DNA would tangle hopelessly
  • ◆Cells that undergo the most division (gut lining, skin, blood) accumulate the most replication errors — explaining why these tissues have the highest cancer rates
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