1. 1 DNA Replication copyright cmassengale

2. 2 Replication Facts DNA has to be copied before a cell dividesDNA has to be copied before a cell divides DNA is copied during the S or synthesis phase of interphaseDNA is copied during the S or synthesis phase of interphase New cells will need identical DNA strandsNew cells will need identical DNA strands copyright cmassengale

3. 3 Synthesis Phase (S phase) S phase during interphase of the cell cycle Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G1G1 G2G2 S phase interphase DNA replication takes place in the S phase. copyright cmassengale

4. DNA Replication DNA must be copied in order for cell reproduction The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing: A-T, G-C Each strand of the original DNA serves as a template for the new strand

5. DNA Replication  Step One - DNA Helicase – Travels down the DNA molecule and “unzips” it by breaking hydrogen bonds between base pairs. The Y-shaped junction of the unwound molecules is a replication fork..

6. 6 DNA Replication Step Two:Step Two: DNA polymerase can then add the new nucleotides to form a new strand of complimentary DNA attached to the split apart strand DNA polymerase can only travel down DNA is a 5’ to 3’ direction, creating a leading strand of DNA and lagging strandDNA polymerase can only travel down DNA is a 5’ to 3’ direction, creating a leading strand of DNA and lagging strand

7. 7 P P P O O O 1 2 3 4 5 5 3 3 5 P P P O O O 1 2 3 4 5 5 3 5 3 G C TA copyright cmassengale Remember DNA Strands are Antiparallel – So both DNA Polymerases will be travel in opposite directions while adding nucleotides, one will have an easy path, the other will have to travel backwards.

8. DNA Replication Copyright Pearson Prentice Hall

9. 9 Synthesis of DNA Strands The Leading Strand single strandThe Leading Strand is synthesized as a single strand from the point of origin toward the opening replication fork, it only needs DNA Polymerase to add nucleotides. This is the easy path. DNA Polymerase Nucleotides 3’5’ copyright cmassengale

10. 10 Synthesis of the New DNA The Lagging Strand is in chunks, not smoothly like the leading strand,The Lagging Strand is synthesized in chunks, not smoothly like the leading strand, against overall direction of replication This strand is made in MANY short segments Lagging Strand 5’ 3’ copyright cmassengale

11. 11 Lagging Strand Segments Okazaki Fragments - lagging strandOkazaki Fragments - series of short segments on the lagging strand Must be joined together by an enzymeMust be joined together by an enzyme Lagging Strand RNAPrimerDNAPolymerase 3’ 5’ Okazaki Fragment copyright cmassengale

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13. DNA Lagging Strand Before RNA primers RNA PrimaseBefore new DNA strands can form on the lagging strand, there must be RNA primers present RNA Primase is the enzyme that synthesizes the RNA Primers – gives DNA polymerase a path to follow After, DNA polymerase adds nucleotides to the lagging strand just like the in the leading strand copyright cmassengale13

14. 14 Third Step: The enzyme DNA Ligase joins the leading strand nucleotides or Okazaki fragments together to make one strandThe enzyme DNA Ligase joins the leading strand nucleotides or Okazaki fragments together to make one strand Lagging Strand Okazaki Fragment 2 DNA ligase DNA ligase Okazaki Fragment 1 5’ 3’ copyright cmassengale

16. DNA Replication Semiconservative Model: From Watson and Crick New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA Parental DNA DNA Template New DNA

17. Short video on Replication https://www.youtube.com/watch ?v=JZXT2uOcD2whttps://www.youtube.com/watch ?v=JZXT2uOcD2w copyright cmassengale17