1 / 33

DNA Replication

DNA Replication. Unit 5B.2. http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg12.html. Starting place = ORIGIN OF REPLICATION Bacteria have one. Bacterial replication. Eukaryotes- multiple origins. Copying DNA. Replication of DNA

holcombs
Download Presentation

DNA Replication

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DNA Replication Unit 5B.2

  2. http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg12.htmlhttp://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg12.html Starting place = ORIGIN OF REPLICATION Bacteria have one Bacterial replication Eukaryotes-multiple origins

  3. Copying DNA • 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 • semi-conservativecopy process

  4. Semi- Conservative Conservative Dispersive

  5. DNA REPLICATION FORK Replication: 1st step • Unwind DNA • Topoisomerase enzyme: unwinds double helix shape • helicase enzyme • Unzips part of DNA helix helicase single-stranded binding proteins replication fork

  6. Replication: 2nd step • Build daughter DNA strand • add new complementary bases • DNA polymerase Where’s theENERGYfor the bondingcome from? DNA Polymerase III

  7. Energy of Replication Where does energy for bonding usually come from? We comewith our ownenergy! energy YourememberATP! ATP ADP ADP modified nucleotide

  8. DNA replication Energy of Replication Where does energy for bonding usually come from? We comewith our ownenergy! energy Are thereother energynucleotides?You bet! And weleave behind anucleotide! ATP AMP modified nucleotide

  9. See animation Energy of Replication • The nucleotides arrive as nucleoside triphosphates • DNA bases with P–P–P • P-P-P = energy for bonding • DNA bases arrive with their own energy source for bonding • bonded by enzyme: DNA polymerase ATP GTP TTP CTP

  10. need “primer” bases to add on to 3 5 Replication DNA Polymerase III • Adding bases • can only add nucleotides to 3 end of a growing DNA strand • need a “starter” nucleotide to bond to • strand only grows 53 3 5

  11. 3 5 Replication energy DNA Polymerase III 3 5

  12. 3 5 Replication energy DNA Polymerase III 3 5

  13. 3 5 Replication 3 5

  14. 5 3 5 3 need “primer” bases to add on to energy Can’t build 3’ to 5’ direction 3 5 3 5

  15. 5 3 5 3 need “primer” bases to add on to 3 5 3 5

  16. need “primer” bases to add on to 5 3 5 3 energy 3 5 3 5

  17. 5 3 5 3 need “primer” bases to add on to energy 3 5 3 5

  18. 5 3 5 3 3 5 3 5

  19. 5 3 5 3 energy 3 5 3 5

  20. ligase 5 3 5 3 Joins fragments 3 5 3 5

  21. Okazaki ligase 3 3 3 3 3 3 3 5 5 5 5 5 5 5 Leading & Lagging strands Limits of DNA polymerase • can only build onto 3 end of an existing DNA strand  Okazaki fragments Lagging strand growing replication fork  Leading strand Lagging strand • Okazaki fragments • joined by ligase • “spot welder” enzyme DNA polymerase III Leading strand • continuous synthesis

  22. DNA polymerase III 3 3 3 3 3 3 3 3 3 3 3 growing replication fork growing replication fork 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 Replication fork / Replication bubble leading strand lagging strand leading strand lagging strand leading strand lagging strand

  23. 3 3 3 3 3 3 DNA polymerase III 5 5 5 5 5 5 Starting DNA synthesis: RNA primers Limits of DNA polymerase • can only build onto 3 end of an existing DNA strand growing replication fork primase RNA RNA primer • built by primase • serves as starter sequence for DNA polymerase

  24. ligase 3 3 3 3 5 5 5 5 Replacing RNA primers with DNA DNA polymerase • removes sections of RNA primer and replaces with DNA nucleotides DNA polymerase I growing replication fork RNA But DNA polymerase I still can only build onto 3 end of an existing DNA strand

  25. 3 3 3 3 5 5 5 5 Houston, we have a problem! Chromosome erosion All DNA polymerases can only add to 3 end of an existing DNA strand DNA polymerase I growing replication fork DNA polymerase III RNA Loss of bases at 5 endsin every replication • chromosomes get shorter with each replication • limit to number of cell divisions?

  26. TELOMERES & TELOMERASE Image from: AP BIOLOGY by Campbell and Reese 7th edition Each replicationshortensDNA strand Primer removed but can’t be replaced with DNA because no 3’ end available for DNA POLYMERASE

  27. TELOMERES-repetitive sequences added to ends of genes to protect information in code • TELOMERASE can add to telomere segments in cells that must divide frequently • Shortening of telomeres may play a role in aging • Cells with increased telomerase activity which allows them to keep dividing EX: Cells that give rise to sperm & eggs, stem cells, cancer cells ANIMATION http://stemcells.nih.gov/info/scireport/appendixC.asp

  28. direction of replication Replication fork DNA polymerase III lagging strand DNA polymerase I 3’ primase Okazaki fragments 5’ 5’ ligase SSB 3’ 5’ 3’ helicase DNA polymerase III 5’ leading strand 3’ SSB = single-stranded binding proteins

  29. Arthur Kornberg 1959 DNA polymerases • DNA polymerase III • 1000 bases/second! • main DNA builder • DNA polymerase I • 20 bases/second • editing, repair & primer removal Thomas Kornberg DNA polymerase III enzyme

  30. Fast & accurate! • It takes E. coli <1 hour to copy 5 million base pairs in its single chromosome • divide to form 2 identical daughter cells • Human cell copies its 6 billion bases & divide into daughter cells in only few hours • remarkably accurate • only ~1 error per 100 million bases • ~30 errors per cell cycle

  31. Editing & proofreading DNA • 1000 bases/second = lots of typos! • DNA polymerase I • proofreads & corrects typos • repairs mismatched bases • removes abnormal bases • repairs damage throughout life • reduces error rate from 1 in 10,000 to 1 in 100 million bases

  32. PROOFREADING & REPAIR Errors can come from: • “proofreading mistakes” that are not caught • Environmental damage from CARCINOGENS (Ex: X-rays, UV light, cigarette smoke, etc) EX: Thymine dimers http://www.personal.psu.edu/staff/d/r/drs18/bisciImages/index.html http://www.mun.ca/biology/scarr/Thymine-Thymine_Dimers.html

  33. NUCLEOTIDE EXCISION REPAIR • Cells continually monitor DNA and make repairs • NUCLEASES-DNA cutting enzyme removes errors • DNA POLYMERASE AND LIGASE can fill in gap and repair using other strand • Xeroderma pigmentosum- genetic disorder • mutation in DNA enzymes that repair UV damage in skin cells • can’t go out in sunlight • increased skin cancers/cataracts http://www.nature.com/jid/journal/v128/n3/images/jid200825i2.jpg http://www.maximilien.asso.fr/images/maxcasque.jpg

More Related