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DNA-Replication biology Lesson 3rd Quarter
- 1. AP Biology 2007-2008 DNA Replication Ch.12.2
- 2. AP Biology SB2 b 2 3/12/2024 Essential Question What is the role of DNA in the process of passing biological traits from one generation to the next?
- 3. AP Biology 3/12/2024 SB2b 3 REPLICATION
- 4. AP Biology 4 Replication of DNA DNA has to copy itself because when new cells are made, the cell has to have an exact copy of the DNA. This occurs during the cell cycle in the S phase. This process is called Replication It is considered semiconservative
- 5. AP Biology DNA Replication Purpose: cells need to make a copy of DNA before dividing so each daughter cell has a complete copy of genetic information 3 proposed Models of Replication
- 6. AP Biology Meselson and Stahl Experiment
- 7. AP Biology Semi-Conservative Model Replication of DNA base pairing allows each strand to serve as a template for a new strand new strand is 1/2 parent template & 1/2 new DNA
- 8. AP Biology Anti-parallel strands Nucleotides in DNA backbone are bonded from phosphate to sugar between 3 & 5 carbons DNA molecule has direction complementary strand runs in opposite direction THIS WILL CAUSE A PROBLEM FOR REPLICATION 3 5 5 3
- 9. AP Biology Bonding in DNA .strong or weak bonds? How do the bonds fit the mechanism for copying DNA? 3 5 3 5 covalent phosphodiester bonds hydrogen bonds
- 10. AP Biology Replication continued Replication begins with DNA untwisting itself and opening up DNA Helicase Responsible for unwinding the molecule The old DNA strands = templates New nucleotides come and bond to the template creating a new strand = Complementary Strand DNA Polymerase Responsible for adding nucleotides Forms covalent bond between nucleotides DNA ligase binds the two new strands
- 12. AP Biology Replication: 1st step Unwind DNA helicase enzyme unwinds part of DNA helix stabilized by single-stranded binding proteins PREVENTS DNA MOLECULE FROM CLOSING! DNA gyrase Enzyme that prevents tangling upstream from the replication fork single-stranded binding proteins replication fork helicase gyrase
- 13. AP Biology Replication: 2nd step RNA Primase Adds small section of RNA (RNA primer) to the 3 end of template DNA Why must this be done? DNA polymerase 3 (enzyme that builds new DNA strand) can only add nucleotides to existing strands of DNA
- 14. AP Biology DNA Polymerase III Replication: 3rd step Build daughter DNA strand add new complementary bases With the help of the enzyme DNA polymerase III
- 15. AP Biology Replication: 4th step Replacement of RNA primer by DNA Done by DNA polymerase I
- 16. AP Biology Limits of DNA polymerase III can only build onto 3 end of an existing DNA strand Leading & Lagging strands 5 5 5 5 3 3 3 5 3 5 3 3 Leading strand Lagging strand ligase Okazaki Leading strand continuous synthesis Lagging strand Okazaki fragments joined by ligase spot welder enzyme DNA polymerase III 3 5 growing replication fork
- 17. AP Biology DNA polymerase III RNA primer is added built by primase serves as starter sequence for DNA polymerase III HOWEVER short segments called Okazaki fragments are made because it can only go in a 5 3 direction DNA replication on the lagging strand 5 5 5 3 3 3 5 3 5 3 5 3 growing replication fork primase RNA
- 18. AP Biology NEXT DNA polymerase I removes sections of RNA primer and replaces with DNA nucleotides STRANDS ARE GLUED TOGETHER BY DNA LIGASE Replacing RNA primers with DNA 5 5 5 5 3 3 3 3 growing replication fork DNA polymerase I RNA ligase
- 19. AP Biology Replication fork 3 5 3 5 5 3 3 5 helicase direction of replication SSB = single-stranded binding proteins primase DNA polymerase III DNA polymerase III DNA polymerase I ligase Okazaki fragments leading strand lagging strand SSB