2. Regents Biology

6. Paired bases  DNA structure  double helix  2 sides like a ladder  Bases match together  A pairs with T  A : T  C pairs with G  C : G

7. Regents Biology Watson and Crick

8. Regents Biology DNA Replication  Replication is semi-conservative (one strand is old, one strand new)  Each strand serves as a template (or pattern) for the new strand

9. Regents Biology Copying DNA  Matching bases allows DNA to be easily copied

10. Regents Biology

11. Making new DNA  Copying DNA  replication  DNA starts as a double-stranded molecule  matching bases (A:T, C:G)  then it unzips…

12. Regents Biology Origins of Replication  Where DNA Replication starts  Differs between organisms  Prokaryotes = 1 origin of replication  Eukaryotes = many different origins of replication

13. Regents Biology

15. DNA replication  Strands “unzip” at the weak bonds between bases

16. Regents Biology General Process of DNA Replication  Step 1: Initiator Proteins  Bind to origins of replication to begin replication  Attracts other enzymes involved in replication process  Step 2:  DNA Helicase separates the DNA helix

17. Regents Biology

18. DNA replication DNA polymerase  Enzyme  DNA polymerase  adds new bases DNA bases in nucleus

19. Regents Biology  Step 3: Primase  Builds a primer at the 5’ end of the new DNA strand  Step 4 :DNA Polymerase III  builds the new strand of DNA in the 5’ to 3’ direction 3’3’ 5’5’ 5’5’

20. Regents Biology -Nitrogenous bases are located in the cytoplasm -They enter the nucleus through the pores in the nuclear membrane

21. Regents Biology DNA Polymerase Copying DNA  Build daughter DNA strand  use original parent strand as “template”  add new matching bases  synthesis enzyme = DNA polymerase

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23. Problem…  How can both strands of DNA be replicated in a 5’- 3’ direction at the same time if they are antiparallel?  Answer: leading and lagging strands

24. Regents Biology Leading and Lagging Strands  Leading strand is synthesized continuously in the direction of replication (goes in the same direction as helicase)  Lagging strand is synthesized in short fragments the opposite direction of replication (opposite direction as helicase)

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26. DNA Ligase  DNA Ligase  Forms covalent bonds between nucleotides to create a continuous strand of DNA  When DNA Polymerase I edits the DNA strand, DNA Ligase attaches the bases on one side of the DNA strand together.

27. Regents Biology DNA Ligase  DNA Ligase seals Okazaki fragments together  Forms covalent bonds between nucleotides to create a continuous strand of DNA

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29. Thymine is added accidentally. DNA polymerase cuts the damaged DNA. The proper base is added. Ligase joins the two spots.

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31. New copies of DNA  Get 2 exact copies of DNA to split between new cells DNA polymerase DNA polymerase

32. Regents Biology Copied Chromosomes

33. Regents Biology DNA Replication  Replicate the following DNA strand:  A – G – G – C – T – T – C – A – G – T  T – C – C – G – A – A – G – T – C - A

34. Regents Biology