2. Searching for Genetic Material  Science as a process Until 1940’s no one new what the genetic material was Until 1940’s no one new what the genetic material was Proteins and DNA were candidatesProteins and DNA were candidates Most scientists thought proteins were the genetic material because of their diversity and size Most scientists thought proteins were the genetic material because of their diversity and size At this time little was known about nucleic acids At this time little was known about nucleic acids

3. Searching for Genetic material  Discovery of genetic role of DNA was in 1928 by Frederick Griffith Studied the bacterium streptococcus pneumoniae ( pneumonia) Studied the bacterium streptococcus pneumoniae ( pneumonia) Used two strains ( pathogenic and harmless) and discovered the process of transformation Used two strains ( pathogenic and harmless) and discovered the process of transformation  Oswald Avery took Griffiths data and found that the only substance capable of transformation was DNA- met with skepticism

5. DNA as the Genetic Material  Evidence for viral DNA Viruses are non-living and are made of little more than DNA surrounded by a protein coat Viruses are non-living and are made of little more than DNA surrounded by a protein coat  Hershey and Chase Used bacteriophages (phages)- viruses that infect bacteria Used bacteriophages (phages)- viruses that infect bacteria Discovered -DNA, not protein, is the hereditary material Discovered -DNA, not protein, is the hereditary material How? How? Implanted radioactive elements ( S and P) into viruses and then let them inject their heredity material into the bacteria and later separated what they did vs. what they did not inject.Implanted radioactive elements ( S and P) into viruses and then let them inject their heredity material into the bacteria and later separated what they did vs. what they did not inject.

7. DNA Structure  Chargaff 1947- reported that the composition of DNA varies from species to species 1947- reported that the composition of DNA varies from species to species Found the in the DNA of each species amount of the bases are not equal but present in a ratio Found the in the DNA of each species amount of the bases are not equal but present in a ratio Found A=T and always C=G Found A=T and always C=G

10. Discovery of the Structure of DNA  Watson & Crick with help from Wilkins and Franklin ( 1950’s) W and C used crystallography photos of DNA, and Chargaff’s data to determine the structure of DNA W and C used crystallography photos of DNA, and Chargaff’s data to determine the structure of DNA Concluded Concluded DNA is a Double Helix of nucleotidesDNA is a Double Helix of nucleotides Thought of DNA as a ladder or a winding stair case made of two strands of nucleotidesThought of DNA as a ladder or a winding stair case made of two strands of nucleotides

12. DNA Bonding and Structure  Double helix is made of nucleotides that are either Purines Purines Adenine and Guanine- double ring structureAdenine and Guanine- double ring structure Pyrimidines Pyrimidines Thymine and Cytosine- single ring structureThymine and Cytosine- single ring structure  Purines always pair with pyrimidines due to structure A always bonds with T forming 3 H-bonds that hold them together A always bonds with T forming 3 H-bonds that hold them together C always bonds with G forming 2 H-bonds that hold them together C always bonds with G forming 2 H-bonds that hold them together  Model explains Chargaffs data

14. Figure 16.5 The double helix

15. How does DNA replicate itself?  3 theories Conservative- Parental molecule remains intact and makes an all new second copy Conservative- Parental molecule remains intact and makes an all new second copy Semi conservative- ( Watson and Crick) two strands of parental molecule separate and each is used as a template for a new strand Semi conservative- ( Watson and Crick) two strands of parental molecule separate and each is used as a template for a new strand Dispersive- each strand of both daughter molecules contains mixture of old and newly made parts Dispersive- each strand of both daughter molecules contains mixture of old and newly made parts

16. DNA Replication

17. DNA Replication: a closer look  Teams of enzymes and other proteins carry out DNA replication Where to start? Where to start? Origin of replication- where replication beginsOrigin of replication- where replication begins Depending on what type of cell can have 1 or many of these ( Pro- 1, Euk- many)Depending on what type of cell can have 1 or many of these ( Pro- 1, Euk- many) Region is recognized by a specific set of nucleotidesRegion is recognized by a specific set of nucleotides At this site DNA will be split open and a replication bubble will form At this site DNA will be split open and a replication bubble will form DNA replication will move in both directions DNA replication will move in both directions

19. DNA Replication  Steps in the process Replication begins at Origin of replication Replication begins at Origin of replication Replication fork forms Replication fork forms DNA helicases bind and unwind the DNA DNA helicases bind and unwind the DNA Single-strand binding proteins stabilize molecule Single-strand binding proteins stabilize molecule DNA polymerase III will begin replication the molecule by pulling nucleotides and attaching them in a complimentary sequence DNA polymerase III will begin replication the molecule by pulling nucleotides and attaching them in a complimentary sequence

20. Problems with DNA Replication  Replication will move in either direction from the origin of replication However, the DNA molecule in anti- parallel- sugar phosphate backbones move in opposite directions However, the DNA molecule in anti- parallel- sugar phosphate backbones move in opposite directions DNA has a 3’ end and a 5’ end DNA has a 3’ end and a 5’ end DNA polymerase will only attach nucleotides to the 3’ end DNA polymerase will only attach nucleotides to the 3’ end Thus DNA molecule can only elongate in the 5’ – 3’ directionThus DNA molecule can only elongate in the 5’ – 3’ direction

22. Solving the problems of DNA replication  Due to anti-parallel structure of DNA one DNA polymerase will move copy in one direction and the other in the opposite Creates a leading and lagging strand Creates a leading and lagging strand Leading strand just moves forwardLeading strand just moves forward Lagging strand make segments ( Okazaki fragments) and then another protein ( DNA ligase) attaches them together to form the final strandLagging strand make segments ( Okazaki fragments) and then another protein ( DNA ligase) attaches them together to form the final strand Almost like backstitching Almost like backstitching

24. Priming DNA synthesis  DNA polymerase can only add nucleotides to an existing polynucleotide that is already pared with the complementary strand DNA polymerase cannot actually initiate synthesis DNA polymerase cannot actually initiate synthesis  Therefore DNA polymerase must start at a primer region Short stretch of RNA( 10 nucleotides) Short stretch of RNA( 10 nucleotides) Primase ( enzyme) is what binds the RNA Primase ( enzyme) is what binds the RNA DNA polymerase III starts here and later another DNA polymerase I goes back and replaces the RNA nucleotides to complete the DNA strand DNA polymerase III starts here and later another DNA polymerase I goes back and replaces the RNA nucleotides to complete the DNA strand

25. Figure 16.14 Priming DNA synthesis with RNA

27. Figure 16.15 The main proteins of DNA replication and their functions

28. DNA Repair  Mismatch repair of nucleotides Repaired by DNA polymerase Repaired by DNA polymerase Proofreads itself and errors only amount to about 1 in 1 billion nucleotides Proofreads itself and errors only amount to about 1 in 1 billion nucleotides  Maintenance repair DNA is subjected to many things and damage DNA is subjected to many things and damage This can result in mutations or changes in the code This can result in mutations or changes in the code Repaired by nuclease- cut out damaged section of DNA and replace with goodRepaired by nuclease- cut out damaged section of DNA and replace with good Called Excision repairCalled Excision repair  Telomere ends- non-coding region of DNA Telomerase replaces lost nucleotides Telomerase replaces lost nucleotides

30. TELOMERES  Impossible on lagging strand to copy the end of 5’ strand  This leaves a gap that would shorten DNA every time it replicates  Telomeres (TTAGGG) repeated many times protects genes by postponing erosion of genes from this shortening effect  Telomerase – lengthens telomeres Contains an RNA sequence that is the template for a telomere Contains an RNA sequence that is the template for a telomere Present in germ cells (for future gametes) Present in germ cells (for future gametes) Increased activity in cancer cells (allows for more cell division) Increased activity in cancer cells (allows for more cell division)

32. Figure 16.19a Telomeres and telomerase: Telomeres of mouse chromosomes