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DNA Replication

DNA Replication. Why Does DNA Need to Replicate?. Your cells are constantly dying and being replaced! White blood cells live for about a year Red blood cells live about 4 months Skin cells last 2-3 weeks Sperm cells die after 3 days

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DNA Replication

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  1. DNA Replication

  2. Why Does DNA Need to Replicate? • Your cells are constantly dying and being replaced! • White blood cells live for about a year • Red blood cells live about 4 months • Skin cells last 2-3 weeks • Sperm cells die after 3 days • Every time your cells divide to produce new cells, DNA must be copied.

  3. ` “It has not escaped our notice that the specific [base] pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” -Watson and Crick

  4. Replication • Nitrogenous bases pair only in one way (A-T, C-G) • One DNA strand serves as a template for a new strand • Replication- the process by which DNA is copied • Ensures that all cells in your body have the same set of genetic information

  5. How is Replication Carried Out? • Enzymes and other proteins help replicate DNA molecules • Replication overview: • Double helix is “unzipped” • Single strand is used as template to build a new, complementary strand • DNA polymerases attach nucleotides to the DNA strand • Results in two identical copies of the DNA molecule

  6. Replication Process • DNA helicase (an enzyme) unzips the DNA strands at multiple places along the molecule. • These are called replication forks or origins of replication

  7. Replication Process • Another enzyme called DNA polymerase bond free-floating nucleotides in the nucleus to their complementary bases on the DNA template strand.

  8. Result of Replication • Two identical double-stranded DNA molecules • Replication is semiconservative • Each new molecule contains one original strand and one new strand

  9. Replication Process • Replication is fast and accurate • Multiple replication forks in eukaryotes allows replication to be completed in just a few hours

  10. Do Mistakes Ever Occur? • DNA polymerase “proofreads” as it goes • Occasionally, it adds the wrong base but can usually detect the error and correct it before moving on. • Replication errors happen only about 1 time per billion nucleotides.

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