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DNA Replication

DNA Replication. 3’. Parental DNA Molecule. 5’. Replication Fork. 3’. 5’. DNA Replication. Origins of replication 1. Replication Forks : hundreds of Y-shaped regions of replicating DNA molecules where new strands are growing. Bubbles. Bubbles. DNA Replication.

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DNA Replication

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  1. DNA Replication

  2. 3’ Parental DNA Molecule 5’ Replication Fork 3’ 5’ DNA Replication • Origins of replication 1. Replication Forks: hundreds of Y-shaped regions of replicating DNA molecules where new strands are growing.

  3. Bubbles Bubbles DNA Replication • Origins of replication 2. Replication Bubbles: a. Hundreds of replicating bubbles (Eukaryotes). b. Single replication fork (bacteria).

  4. DNA Replication • Strand Separation: 1. Helicase: enzyme which catalyze the unwinding andseparation(breaking H- Bonds) of the parental double helix. 2. Single-Strand Binding Proteins: proteins which attach and help keep the separated strands apart.

  5. Enzyme Enzyme DNA DNA Replication • Strand Separation: 3. Topoisomerase: enzyme which relieves stresson theDNA moleculeby allowing free rotation around a single strand.

  6. DNA Replication • Priming: 1. RNA primers: before new DNA strands can form, there must be small pre-existing primers (RNA)present to start the addition of new nucleotides (DNA Polymerase). 2. Primase: enzyme that polymerizes (synthesizes) the RNA Primer.

  7. 5’ 3’ 5’ RNA Primer DNA Polymerase Nucleotide DNA Replication • Synthesis of the new DNA Strands: 1. DNA Polymerase: with a RNA primer in place, DNA Polymerase (enzyme) catalyze the synthesis of a new DNA strand in the 5’ to 3’ direction.

  8. 5’ 3’ 5’ RNA Primer DNA Polymerase Nucleotides DNA Replication 2. Leading Strand: synthesized as a single polymerin the 5’ to 3’ direction.

  9. Leading Strand 5’ 3’ 3’ 5’ DNA Polymerase RNA Primer 5’ 3’ 5’ 3’ Lagging Strand DNA Replication 3. Lagging Strand: also synthesized in the 5’ to 3’ direction, but discontinuously against overall direction of replication.

  10. DNA Polymerase Okazaki Fragment RNA Primer 5’ 3’ 5’ 3’ Lagging Strand DNA Replication 4. Okazaki Fragments: series of short segments on the lagging strand.

  11. DNA ligase Okazaki Fragment 1 Okazaki Fragment 2 5’ 3’ 3’ 5’ Lagging Strand DNA Replication 5. DNA ligase: a linking enzyme that catalyzes the formation of a covalent bond from the 3’ to 5’ end of joining stands. Example: joining two Okazaki fragments together.

  12. Question: • What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

  13. Answer: DNA 5’-GCGTATG-3’ DNA 3’-CGCATAC-5’

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