2. AP Biology 2006-2007 Nucleic Acids Information storage

3. AP Biology proteins DNA Nucleic Acids  Function:  genetic material  stores information  genes  blueprint for building proteins DNA  RNA  proteins  transfers information  blueprint for new cells  blueprint for next generation

4. AP Biology Nucleic Acids  Examples:  RNA (ribonucleic acid)  single helix  DNA (deoxyribonucleic acid)  double helix  Structure:  monomers = nucleotides RNADNA

5. AP Biology Nucleotides  3 parts  nitrogen base (C-N ring)  pentose sugar (5C)  ribose in RNA  deoxyribose in DNA  phosphate (PO 4 ) group Are nucleic acids charged molecules? Nitrogen base I’m the A,T,C,G or U part!

6. AP Biology Types of nucleotides  2 types of nucleotides  different nitrogen bases  purines  double ring N base  adenine (A)  guanine (G)  pyrimidines  single ring N base  cytosine (C)  thymine (T)  uracil (U) Purine = AG Pure silver!

7. AP Biology Nucleic polymer  Backbone  sugar to PO 4 bond  phosphodiester bond  new base added to sugar of previous base  polymer grows in one direction  N bases hang off the sugar-phosphate backbone Dangling bases? Why is this important?

8. AP Biology Pairing of nucleotides  Nucleotides bond between DNA strands  H bonds  purine :: pyrimidine  A :: T  2 H bonds  G :: C  3 H bonds Matching bases? Why is this important?

9. AP Biology DNA molecule  Double helix  H bonds between bases join the 2 strands  A :: T  C :: G H bonds? Why is this important?

10. AP Biology Copying DNA  Replication  2 strands of DNA helix are complementary  have one, can build other  have one, can rebuild the whole Matching halves? Why is this a good system?

11. AP Biology When does a cell copy DNA?  When in the life of a cell does DNA have to be copied?  cell reproduction  mitosis  gamete production  meiosis

12. AP Biology 2007-2008 DNA Replication

13. AP Biology Directionality of DNA  You need to number the carbons!  it matters! OH CH 2 O 4 5 3 2 1 PO 4 N base ribose nucleotide This will be IMPORTANT!!

14. AP Biology The DNA backbone  Putting the DNA backbone together  refer to the 3 and 5 ends of the DNA  the last trailing carbon OH O 3 PO 4 base CH 2 O base O P O C O –O–O CH 2 1 2 4 5 1 2 3 3 4 5 5 Sounds trivial, but… this will be IMPORTANT!!

15. 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 3 5 5 3

16. 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

17. AP Biology Base pairing in DNA  Purines  adenine (A)  guanine (G)  Pyrimidines  thymine (T)  cytosine (C)  Pairing  A : T  2 bonds  C : G  3 bonds

18. AP Biology 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-conservative copy process

19. AP Biology DNA Replication  Large team of enzymes coordinates replication Let’s meet the team…

20. AP Biology Replication: 1st step  Unwind DNA  helicase enzyme  unwinds part of DNA helix  stabilized by single-stranded binding proteins single-stranded binding proteins replication fork helicase I’d love to be helicase & unzip your genes…

21. AP Biology DNA Polymerase III Replication: 2nd step But… We’re missing something! What? Where’s the ENERGY for the bonding!  Build daughter DNA strand  add new complementary bases  DNA polymerase III

22. 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 Okazaki fragments ligase Okazaki Leading strand  continuous synthesis Lagging strand  Okazaki fragments  joined by ligase  “spot welder” enzyme DNA polymerase III  3 5 growing replication fork

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

24. AP Biology DNA polymerases  DNA polymerase III  1000 bases/second!  main DNA builder  DNA polymerase I  20 bases/second  editing, repair & primer removal DNA polymerase III enzyme Arthur Kornberg 1959 Thomas Kornberg ??

25. AP Biology 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