1. Mutations in Replication 289-291

2. What did you learn in your reading? Who performs mismatch repair? Why does DNA constantly have to be maintained? What is excision repair? What is the end-replication problem? Who fixes it?

3. Randoms… Haploid cell (sperm/egg) have about 3 billion base pairs Approximately 100-200 million base pairs per chromosome Initial pairing errors are 1 in 10,000 At the end of the completed strand, only 1 in 1 billion have errors There are 2 types of repair…

4. Mismatch Repair vs Damage Repair DNA polymerase proofreads and fixes mistakes before the strand is complete Many other proteins also perform mismatch repair Reactive chemicals, radioactive emissions, X-rays, and UV rays are constantly (potentially) harming DNA Cell continuously monitors and repairs

5. Excision Repair Nuclease: cuts damaged portion DNA polymerase adds new nucleotides Ligase seals DNA back up

6. Xeroderma pigmentosum Disorder in the excision-repair enzyme Skin cells mutations are not corrected after UV damage

7. Replication Problem DNA polymerase can only add nucleotides to the 3’ end of a preexisting polynucleotide So….. Where primer is removed a gap remains unfilled If it would stay this way, each new cell would be shorter and shorter until no DNA would remain **Only a problem in eukaryotes…why??

8. Telomeres and Telomerase Telomere: special nucleotide sequence at ends of DNA – TTAGGG is typical human repeating telomere Telomerase: enzyme that catalyzes the lengthening of telomeres with the help of RNA strand Job of telomere: – Protect the genes from being eroded from generation to generation of replication – Prevent the ends from activating cell death (unnecessarily)

9. Telomerase http://highered.mcgraw- hill.com/sites/dl/free/0072835125/126997/an imation19.html http://highered.mcgraw- hill.com/sites/dl/free/0072835125/126997/an imation19.html

10. Telomeres and Aging http://player.discoveryeducation.com/index.cf m?guidAssetId=AB274EB9-EDF1-40F0-9122- 5B996E8E08E0&blnFromSearch=1&productco de=US http://player.discoveryeducation.com/index.cf m?guidAssetId=AB274EB9-EDF1-40F0-9122- 5B996E8E08E0&blnFromSearch=1&productco de=US

11. Sickle Cell and Malaria http://www.pbs.org/wgbh/evolution/library/01/ 2/quicktime/l_012_02.html http://www.pbs.org/wgbh/evolution/library/01/ 2/quicktime/l_012_02.html How can a mutation be harmful in one environment and helpful in another? Why should a mutation persist if it kills people? Why are there more people with sickle cell disease in one part of the world than in other parts?

12. Cracking the Code http://video.pbs.org/video/1841308959/ 15:27 (time to start clip) How can a mutation in a single DNA base affect the production of normal proteins? How are mutations passed on to offspring? What does it mean to be a carrier of a disease? What is the pattern of inheritance for diseases carried by recessive genes? What is Tay Sachs?

13. Cracking the Code http://www.teachersdomain.org/resource/tdc 02.sci.life.gen.modification/ http://www.teachersdomain.org/resource/tdc 02.sci.life.gen.modification/ What are some possible future uses of genetic technology? If future technology allows it, do you think parents should be able to choose specific characteristics for their babies? Do the benefits of new genetic tools outweigh the risks?