AP Biology Nucleic Acids Information storage

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

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

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!

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!

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?

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?

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

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?

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

AP Biology DNA Replication

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

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 Sounds trivial, but… this will be IMPORTANT!!

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

AP Biology Bonding in DNA ….strong or weak bonds? How do the bonds fit the mechanism for copying DNA? covalent phosphodiester bonds hydrogen bonds

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

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

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

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…

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

AP Biology Limits of DNA polymerase III  can only build onto 3 end of an existing DNA strand Leading & Lagging strands 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

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

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 ??

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