ap biology unit 6

• in the 1950s rosalind franklin preformed ____

  x ray crystallography of DNA
• what did edwin chargaff find

  that the amount of adenine equals the amount of thymine, and the amount of cytosine equals the amount of guanine
• purines


  double ring structure
• pyrimidines


  single ring structure

  -“small structure big name”
• adenine and thymine have __ hydrogen bonds


  2
• cytosine and guanine have __ hydrogen bonds

  3
• what did watson and crick do


  they combined the findings of franklin and chargaff to create the first 3d double helix model of DNA
• dna is a 


  double stranded helix
• backbone of dna


  sugar phosphate
• center of dna


  nucleotide pairing
• dna strands are 


  antiparallel
• 5 prime end of dna


  free phosphate group
• 3 prime end of dna

  free hydroxyl group
• dna is the primary source of

  heritable information
• eukaryotic cells


  dna is found in the nucleus

  linear chromosomes
• prokaryotic cells


  dna is found in the nucleotide region

  chromosomes are circular
• plasmids 


  small circular dna molecules that are separate from the chromosomes
• plasmids replicate ______ from the chromosomal dna

  independently
• plasmids are primarily found in

  prokaryotes
• when the ____ plasmid is inserted back into the bacteria the ___ will be _____

  recombinant, gene, expressed
• bacteria can ______ ____ found on plasmids with neighbouring bacteria

  exchange genes
• rna

  ribonucleic acid

  single stranded ribose sugar and phosphate backbone
• dna


  deoxyribosenucleic acid

  double stranded deoxyribose sugar and phosphate backbone
• 3 models for dna replication

  conservative, semi conservative, dispersive
• conservative model

  the parental strands direct synthesis of: an entirely new double stranded molecule
• semi conservative model


  the two parental strands each make a copy of itself

  -after one round of replication, the two daughter molecules each have one parental and one new strand
• dispersive model


  the material in the two parental strands is dispersed randomly between the two daughter molecules

  -after one round of replication the daughter molecules contain a random mix of parental and new dna
• meselson and stahls experiment


  1.bacteria was cultured with a heavy isotope 15N

  2.bacteria was transferred to a medium with 14N, a light isotope

  3.dna was centrifuged and analyzed after each replication
• 1st step in dna replication


  dna replication begins at sites called origins of replication

  -various proteins attach to the origin of replication and open dna to form a replication fork
• 2nd step in dna replication

  the enzyme helicase will unwind dna strands at each replication fork

  -ssbps (single strand bonding proteins) bind to the dna to keep it from reforming hydrogen bonds between nucleotide base pairs

  -topiosomerase will help prevent strain ahead of the replication fork by relaxing supercoiling
• 3rd step in dna replication 


  the enzyme primase initiates replication by adding short segments of rna, called primers to the parental dna strand

  -enzymes that synthesize dna can only attach new dna nucleotides to an existing strand

  -primers serve as the foundation for dna synthesis
• 4th step in dna replication 


  antiparallel elongation

  -dna polymerase 3 attaches to each primer on the parental strand and moves in the 3 to 5 prime direction

  -as it moves it adds nucleotides to the new strand in the 5 to 3 prime direction

  -the dnap 3 that follows helicase is known as the leading strand and it only requires 1 primer

  -the dnap 3 on the other parental strand that moves away from helicase is known as the lagging strand and it requires many primers
• 5th step in dna replication


  the leading strand is synthesized in one continuous segment, but since the lagging strand moves away from the replication fork it is synthesized in chunks
• 6th step in dna replication

  after dnap 3 forms an okazaki fragment, dnap 1 replaces rna nucleotides with dna nucleotides
• okazaki fragments 


  segments of the lagging strand
• since dnap 3 can only add nucleotides to a 3 prime end, there is no way to finish _____ on the 5 prime end of a ______

  replication, lagging strand
• over many replications this would mean that the dna would become ____

  shorter
• telomeres

  repeating units of short nucleotide sequences that do not code for genes

  -form a cap at the end of dna to help postpone erosion

  -the enzyme telomerase adds telomeres to dna
• as ______ adds nucleotides to the new dna strand, it proofreads the bases added

  dna polymerase
• if errors still occur ____ will take place

  mismatch repair