DNA Replication

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DNA replication Molecular biology

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DNA Replication:

DNA Replication

DNA Replication:

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

DNA Replication:

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

DNA Replication:

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

DNA Replication:

DNA Replication Strand Separation : 3. Topoisomerase : enzyme which relieves stress on the DNA molecule by allowing free rotation around a single strand. Enzyme DNA Enzyme

DNA Replication:

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 .

DNA Replication:

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 . RNA Primer DNA Polymerase Nucleotide 5’ 5’ 3’

DNA Replication:

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

DNA Replication:

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

DNA Replication:

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

DNA Replication:

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. Lagging Strand Okazaki Fragment 2 DNA ligase Okazaki Fragment 1 5’ 5’ 3’ 3’