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Frederick Griffith, in the 1920's, discovered the ____ ____.
What did Frederick Griffith study in order to discover the transforming principle?
R strain & S strain Streptococcus Pneumoniae
What are 4 characteristics of S strain Streptococcus bacterium?
- Shiny, Smooth colonies
- Mice died within a day of being injected
What are 3 characteristics of R strain Streptococcus bacterium?
- Rough looking colonies
- NOT capsulated
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
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
Who discovered that the Griffith's transforming principle was actually DNA & when?
Avery, McCleod & McCarty in 1944
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
After doing their experiments, Avery, McCleod & McCarty, concluded that . . . .
Transforming principle was indeed DNA
What 2 scientists actually confirmed that DNA is indeed genetic material & when?
Hershey & Chase in 1952
What does a bacteriaphage do?
- Lands on a cell
- Injects bacterial DNA
- DNA replicates
- Cells Explode
- Bacteria goes everywhere
The T2 bacteriaphages utilized by Hershey & Chase were ____ that had their ___ packed in a protein coat.
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
After material is run thru a centrifuge the pellet is the ____ portion at the ____ & the supernatant is the ____ portion.
In Hershey & Chases experiment, what was found to be in the supernatant?
Sulfur & thus viral protein
In Hershey & Chases experiment, what was found to be in the pellet?
Compacted cells w/ phosphorus & thus viral DNA
What was the conclusion of Hershey & Chases experiment?
DNA enters bacterial cell & is responsible for reproduction of new viruses.
Who determined the DNA NOT protein is genetic material?
Hershey & Chase
Who used X-ray crystallography to help to determine DNA structure & when?
Rosalind Franklin & Maurice Wilkins in the 1950s
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
What did crystallographs taken by Franklin & Wilkins infer about DNA structure?
That it was spiral or helical in shape
What did Erwin Chargaff determine in the 1950's?
Proportions of nucleotides in DNA
Explains Chargaff's rule.
Purines = Pyrimidines in DNA
Chargaff's observations suggested the idea of ___ ___ ___ of DNA.
Complimentary base pairing
James Watson & Francis Crick did what in 1953?
Utilized model building to est. general structure of DNA - Double helix
What 3 results of previous experiments did Watson & Crick utilize?
- X-ray crystalography
- Chargaff's rule
- Pauling's near miss
What did Arthur Kornberg demonstrate in 1956?
That DNA has info needed for its own replication
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
Who determined that DNA replication IS a semi conservative process & when?
Matthew Meselson & Franklin Stahl in 1957
Meselson & Stahl utilized a procedure called ____ ____.
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
Nucleotides are made up of what 3 parts?
- 5 C sugar (deoxyribose)
- Phosphate Grp
- Nitrogenous base
What are the 4 nitrogenous bases that could make up a nucleotide?
What are the complimentary base pairs in nucleotides?
- Thymine prs w/Adenine
- Guanine prs w/Cytosine
What type of bond holds complimentary base prs together in a nucleotide?
The purines are ___ & ___ and the pyrimidines are the ___ & ___.
- Guanine & Adenine
- Cytosine & Thymine
The type of DNA replication where each parent strand serves as a template for a new strand is ____ replication.
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
The ____ strand runs fr 3' to 5' in the correct orientation for new nucleotides.
The ____ strand runs fr 5' to 3' & is in reverse orientation.
When the lagging strand in DNA replicates it does so in sm sections called ____ ____.
Okazaki fragments contain about how many nucleotides?
What is the function of the DNA helicase?
Unwinds double helix at the Ori into 2 forks
Each new strand of DNA must be started by a ____ made of ___.
The ____ forms an RNA primer.
What eventually happens to the RNA primer?
DNA polymerase I hydrolyzes RNA & replaces it w/DNA
___ ____ adds new nucleotides to the growing chain starting at the ___ end.
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
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
___ ___ catalyzes formation of phosphodiester linkage that joins Okazaki fragments together.
In prokaryotic cells 2 interlocking circular DNAs are formed separated by the enzyme ____.
DNA replication in prokaryotic cells is short & circular & has ____ origin whereas in eukaryotic cells replication is ___ & ____ & has 100s of oris.
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
What are the 3 types of DNA repair mechanisms?
- Mismatch repair
- Excision repair
Which form of DNA repair mechanism corrects errors during the replication process?
Explain the proofreading repair mechanism.
DNA polymerase proofreads its work during replication
What is the error rate of the replication complex?
1 in 10,000 base prs
The repair mechanism that scans & repairs errors after replication is called ____ ____.
What errors is mismatch repair designed to get?
Anything missed by DNA polymerase
What repair mechanism operates over the life of the cell & repairs errors resulting fr chem or radiation damage?
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