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Frederick Griffith, in the 1920's, discovered the ____ ____.
Transforming Principle
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What did Frederick Griffith study in order to discover the transforming principle?
R strain & S strain Streptococcus Pneumoniae
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What are 4 characteristics of S strain Streptococcus bacterium?
- Shiny, Smooth colonies
- Capsulated
- Virulent
- Mice died within a day of being injected
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What are 3 characteristics of R strain Streptococcus bacterium?
- Rough looking colonies
- NOT capsulated
- Nonvirulent
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What happened to Griffith's mice when they were injected w/dead S strain bacterium mixed w/live R strain & why?
Mice died b/c S & R procreated & gene for capsulation transfered to R strain
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What were Griffith's 2 conclusions?
- Living R strain transformed by presence of dead S strain
- S & R strains procreate & gene for capsulation transfered to R
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Who discovered that the Griffith's transforming principle was actually DNA & when?
Avery, McCleod & McCarty in 1944
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When Avery, McCleod & McCarty discovered that Griffith's transforming principle was actually DNA what were 2 reasons it wasn't readily accepted?
- It was believed that DNA was too simple to be genetic material
- Little known about bacterial genetics
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After doing their experiments, Avery, McCleod & McCarty, concluded that . . . .
Transforming principle was indeed DNA
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What 2 scientists actually confirmed that DNA is indeed genetic material & when?
Hershey & Chase in 1952
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What does a bacteriaphage do?
- Lands on a cell
- Injects bacterial DNA
- DNA replicates
- Cells Explode
- Bacteria goes everywhere
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The T2 bacteriaphages utilized by Hershey & Chase were ____ that had their ___ packed in a protein coat.
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What 2 radioactive tracers did Hershey & Chase utilize & why?
- Sulfur b/c its present in protein but not in DNA
- Phosphorus b/c its present in DNA but not in protein
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After material is run thru a centrifuge the pellet is the ____ portion at the ____ & the supernatant is the ____ portion.
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In Hershey & Chases experiment, what was found to be in the supernatant?
Sulfur & thus viral protein
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In Hershey & Chases experiment, what was found to be in the pellet?
Compacted cells w/ phosphorus & thus viral DNA
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What was the conclusion of Hershey & Chases experiment?
DNA enters bacterial cell & is responsible for reproduction of new viruses.
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Who determined the DNA NOT protein is genetic material?
Hershey & Chase
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Who used X-ray crystallography to help to determine DNA structure & when?
Rosalind Franklin & Maurice Wilkins in the 1950s
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Why did Franklin & Wilkins use X-ray crystallography to try to determine the shape of DNA?
B/c the positions of atoms could be inferred fr the diffraction of X-ray being passed thru
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What did crystallographs taken by Franklin & Wilkins infer about DNA structure?
That it was spiral or helical in shape
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What did Erwin Chargaff determine in the 1950's?
Proportions of nucleotides in DNA
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Explains Chargaff's rule.
Purines = Pyrimidines in DNA
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Chargaff's observations suggested the idea of ___ ___ ___ of DNA.
Complimentary base pairing
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James Watson & Francis Crick did what in 1953?
Utilized model building to est. general structure of DNA - Double helix
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What 3 results of previous experiments did Watson & Crick utilize?
- X-ray crystalography
- Chargaff's rule
- Pauling's near miss
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What did Arthur Kornberg demonstrate in 1956?
That DNA has info needed for its own replication
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Kornberg showed that DNA can replicate itself in a test tube if you have what 3 ingredients?
- Template for DNA
- DNA polymerase
- Mix of 4 nucleotides
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Who determined that DNA replication IS a semi conservative process & when?
Matthew Meselson & Franklin Stahl in 1957
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Meselson & Stahl utilized a procedure called ____ ____.
Density Labeling
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What were Meselson & Stahl's 3 conclusions?
- DNA replication is semi conservative
- If replication was conservative then only heavy & light bands yielded
- If replication dispersive then there would be no intermediate band in 2nd generation
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Nucleotides are made up of what 3 parts?
- 5 C sugar (deoxyribose)
- Phosphate Grp
- Nitrogenous base
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What are the 4 nitrogenous bases that could make up a nucleotide?
- Adenine
- Thymine
- Guanine
- Cytosine
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What are the complimentary base pairs in nucleotides?
- Thymine prs w/Adenine
- Guanine prs w/Cytosine
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What type of bond holds complimentary base prs together in a nucleotide?
Hydrogen Bonds
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The purines are ___ & ___ and the pyrimidines are the ___ & ___.
- Guanine & Adenine
- Cytosine & Thymine
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The type of DNA replication where each parent strand serves as a template for a new strand is ____ replication.
Semi-conservative
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What are 2 postulates of semi-conservative replication?
- Each parent strand act as template for new strand
- Each new double helix has 1 parent strand & 1 new strand
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The ____ strand runs fr 3' to 5' in the correct orientation for new nucleotides.
Leading
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The ____ strand runs fr 5' to 3' & is in reverse orientation.
Lagging
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When the lagging strand in DNA replicates it does so in sm sections called ____ ____.
Okazaki Fragments
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Okazaki fragments contain about how many nucleotides?
100-200
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What is the function of the DNA helicase?
Unwinds double helix at the Ori into 2 forks
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Each new strand of DNA must be started by a ____ made of ___.
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The ____ forms an RNA primer.
Primase
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What eventually happens to the RNA primer?
DNA polymerase I hydrolyzes RNA & replaces it w/DNA
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___ ____ adds new nucleotides to the growing chain starting at the ___ end.
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There are multiple types of DNA polymerases. The 2 purposes we were told are . . . .
- 1 is responsible for replication
- Others remove primers or repair DNA
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What are 3 characteristics of the structure of DNA polymerases?
- Much larger than substrates
- Shaped like hand w/finger regions that rotate inward
- Fingers have precise shapes that recognize shapes of bases
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___ ___ catalyzes formation of phosphodiester linkage that joins Okazaki fragments together.
DNA Ligase
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In prokaryotic cells 2 interlocking circular DNAs are formed separated by the enzyme ____.
Topoisomerase
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DNA replication in prokaryotic cells is short & circular & has ____ origin whereas in eukaryotic cells replication is ___ & ____ & has 100s of oris.
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What are the 2 major steps in DNA replication?
- Double helix is unzipped by the helices
- Nucleotides are added to 3' (OH) end of growing polynucleotide chain
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What are the 3 types of DNA repair mechanisms?
- Proofreading
- Mismatch repair
- Excision repair
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Which form of DNA repair mechanism corrects errors during the replication process?
Proofreading
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Explain the proofreading repair mechanism.
DNA polymerase proofreads its work during replication
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What is the error rate of the replication complex?
1 in 10,000 base prs
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The repair mechanism that scans & repairs errors after replication is called ____ ____.
Mismatch repair
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What errors is mismatch repair designed to get?
Anything missed by DNA polymerase
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What repair mechanism operates over the life of the cell & repairs errors resulting fr chem or radiation damage?
Excision repair
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