TOPIC A BIOL 207

• 4 properties of genetic information

  1. Information: contain instruction necessary to create an organism
  2. replication: can be copies
  3. transmission: can be passed from parents to offspring during reproduction
  4. variation: can be changed to account for variable phenotypes
• Landmark experiment identified DNA was the hereditary material
• Frederic Griffith experiment

  • Study mice with S(smooth cells) that kill mice and R(rough cells) that don't kill mice
  • conclude that S cell can transfer information to R cell and transforming them into S cells
  • concept of transformation
  • change in an organism due to uptake of external DNA by a cell
• Avery, Macleod and McCarty experiment

  • adding proteinase, ribonuclease and deoxyribonuclease to remove protein, RNA and DNA to see which material is transforming R cell to S cell
  • conclude that after remove DNA, no transforming happens so DNA is the genetic material
• Hershey and Chase experiment

  • use radioactive Phosphorus to label DNA and radioactive Sulfur to label protein
  • conclude that radioactive phosphorus are found in bacterial pellet and radioactive sulfur are found in the supernatant so DNA is the genetic material
• which 3 people contribute to Waston and Crick DNA model?

  Phoebus Levine

  Rosalind Franklin

  Erwin Chargaff
• Phoebus Levine

  • study the building block of DNA
  • know that purines AG and pyrimidines TC
  • phosphate group
  • deoxyribose sugar
• What is the ribose and deoxyribose form of adenine?

  Ribose: Adenosine Deoxyribose: Deoxyadenosine
• what is the ribose and deoxyribose form of cytosine?

  cytidine annd deoxycytidine
• what is the ribose and deoxyribose form of thymine?

  ribose: none

  deoxy: deoxythymidine
• what is the ribose and deoxyribose form of guanine?

  Ribose: Guanosine Deoxyribose: Deoxyguanosine
• what is the ribose and deoxyribose form of uracil?

  ribose: uridine

  deoxy: none
• 5’ to 3’ polarity is created by the position of phosphodiester bonds
• what type of bond is phosphodiesteer bond?

  Covalent
• Phosphates + sugars = negatively-charged backbone of nucleic acid
• Strand is directional based on orientation of sugar molecules in DNA.

  • based on the 5'C of sugar or 3'OH placement
• Rosalind Franklin

  • use X rays crystallography to determine DNA is helix
• Erwin Chargaff

  • use chemical analysis to determine the distribution of nitrogen bases in DNA
  • Chargaff rules
  • A=T and C=G
  • A+G=T+C
• Key feature in Waston and Crick model

  1. double helix
  2. strand run from 5' to 3'
  3. complementary base pairing (A=T,C=G)
  4. sugar and phosphate face OUT and nitrogenous base face in
  5. diameter is 20 amstrong =2nm
  6. purine always pair with a pyrimidines for constant diameter
  7. hydrogen bound between nitrogenous base (weak)
  8. 2 H bond between AT and 3 in CG
  9. adjacent nucleotide on same strand linked by phosphodiester bond
  10. There are 10 nitrogenous base per 360° turn of the helix
• Meselson-Stahl experiment

  • identify mechanism of DNA replication
  • uses N15 heavy media to turn DNA content heavy then transfer to N14 media for DNA to replicate and observed the band
  • conclude that DNA replicated semi conservative
• what would a band for conservative model look like?

  2 band of completely heavy and completely light
• what would a band for semiconservative model look like?

  1st generation - heavy band of 15N14N hybrid DNA

  2nd generation= 2 band, 1 of 14 band and 1 of 15N14N hybrid band
• what will the band look like for dispersive model?

  both 1st and 2 generation have hybrid 15N14N DNA, there will be more 14N DNA becasue they are on 14N medium
• where do replication start?

  Ori C
• Ori C

  • site of initiation (replication)
  • fixed location
  • about 275 base pair
  • GATC methylation site
  • 5 Dna A boxes
  • 3 AT rich region
  • replication forks
• GATC methylation site

  • methyl group added to "A" nucleotide if methylase sees a GATC sequence
• 5 Dna A boxes

  • 9 Nucleotide long
  • Binding of DNA A protein causes aa conformational change
  • change in shape of DNA
• 3 AT rich region

  • 13 nucleotide long
  • fewer H bond bc AT is double bond
  • torisonal stress in stand results in denaturation or melting of DNA duplex
  • causing 2 strand of AT rich region to open
• replication forks

  • site of active DNA replication
  • where 2 parent strands are being unwound
  • bidirectional replication
• Why dis DNA synthessis only goes from 5' to 3'?

  because DNA polymerase can only add new base to the 3' OH
• DNA replication in all organisms:

  1. Is initiated at origin of replication (ori)
  2. Occurs only in the 5’ to 3’ direction
  3. Is semi-conservative
  4. Proceeds at replication forks
  5. Occurs bidirectionally
  6. Includes both leading strand and lagging strand synthesis
  7. Uses breakage of the high energy triphosphate bond of dNTPs (dATP, dGTP, dCTP and dTTP) as the source of energy
• Leading strand synthesis is continuous because the direction of replication moves in the same direction as the replication fork opens.
• lagging strand synthesis is discontinuous because replication occurs in the opposite direction as the replication fork opens there is no way to extend the existing 5’ end of the new strand

  • okazaki fragment
• what are 7 key player in DNA replication

  1. helicase
  2. Topoisomerase
  3. Single stranded binding protein
  4. Primase
  5. DNA polymerase III
  6. DNA polymerase I
  7. DNA Ligase
• Helicase

  enzyme that denature DNA double strand turning them into single strand
• Single stranded Binding Protein

  • prevent denaturation of DNA duplex before replication
  • keep them as single strand, prevent them from falling back together
• Topoisomerase

  • enzyme to relieve stress created by helicase unwinding motion
  • come before helicase
• Primase

  • enzyme that adds RNA primer
• Why does RNA primer needed in DNA replication?

  because DNA polymerase can't start from scrap
• DNA polymerase III

  • t' to 3' polymerase function, adding nucleotide
  • 3' to 5' function, exonuclease function
  • sense mistake in base pairing, move backward to remove mistake then continue