1. DNA Replication Packet #
Tuesday, November 13, 2018

2. Historical DNA Discoveries
1928
Federick Griffith finds a substance in heat-killed bacteria that “transforms” living bacteria
1944
Oswald Avery, Cloin MacLeod and Maclyn McCarty chemically identify Griffith’s transforming principle as DNA
1949
Erwin Chargaff reports relationships among DNA bases that provide a clue to the structure of DNA
1953
Alfred Hersey and Martha Chase demonstrate that DNA , not protein, is involved in viral reproduction.
Rosalind Franklin produces an x-ray diffraction image of DNA
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3. Historical DNA Discoveries II
1953
James Watson and Francis Crick propose a model of the structure of DNA.
1958
Matthew Meselson and Franklin Stahl demonstrate that DNA replication is semi conservative replication
1962
James Watson, Francis Crick and Maurice Wilkins are awarded the Nobel Prize in Medicine for discoveries about the molecular structure of nucleic acids.
1969
Alfred Hershey is awarded the Nobel Prize in Medicine for discovering the replication mechanism and genetic structure of viruses
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4. Homework Assignment Know Griffith’s Transformation Experiments
Know The Hershey-Chase Experiments
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5. Griffith Experiment
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6. Hershey Chase Experiment
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7. Nucleotides
Nucleotide subunits link together to form a single DNA strand
DNA Nucleotides
Nucleotides are the building blocks of nucleic acids
Phosphate
Sugar
Deoxyribose
Base
Purines (Two Rings)
Adenine
Guanine
Pyrimidines (One Ring)
Thymine
Cytosine
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8. Nucleotides II
Nucleotides are linked together by covalent phosphodiester bonds
Each phosphate attaches to the 5’ end of one deozyribose and to the 3’ carbon of the neighboring deoxyribose
Makes up the sugar-phosphate backbone
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9. DNA Strand
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10. Orientation of DNA
Each DNA molecule consists of two polynucleotide chains that associate as a double helix
The two chains run antiparallel
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11. DNA Double Helix
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12. Base-Pairing Rules for DNA Chargaff Rules
Hydrogen bonds hold the chains of the double helix together
Adenine forms two hydrogen bonds with thymine
Guanine forms three hydrogen bonds with cytosine
Chargaff’s rules
A always pairs with T
G always pairs with C
Complementary base pairing
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13. Chargaff Rules
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14. Chargaff’s Rules II
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15. Models of DNA Replication
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16. Semi-conservative Replication
When Ecoli cells are grown for many generations in a medium containing heavy nitrogen, 15N they incorporate the 15N into their DNA.
When researchers transfer cells from a 15N medium to a 14N medium and isolate them after either one or two generations, the density of the DNA in each group is what would be expected if DNA replication were semi conservative.
In semi conservative replication, each daughter double helix consists of an original strand from the parent molecule and a newly synthesized complementary strand.
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17. DNA Replication Introduction
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18. Introduction to the Strands
Template Strands {The Parental Strands}
Are the strands being copied
The original DNA strands
During DNA replication, both strands are copied
This means that there are TWO template strands
Complementary Strands {The Daughter Strands}
The NEW DNA strands produced from the Template Strands
During DNA replication, there are TWO complementary strands
Always remember that the process started with TWO template strands
Tuesday, November 13, 2018

19. Introduction to DNA Replication
DNA replication is bidirectional and starts at the origin of replication
The process proceeds in both directions from that point.
A eukaryotic chromosome may have multiple origins of replication
Allows the process to occur faster and more efficient
DNA replication/synthesis, of the complementary strands, proceed in a 5’ to 3’ direction.
Nucleotides can ONLY be added to the 3’ end.
This causes one of the complementary strands to be produced continuously and the other discontinuous
The continuous strand is called the leading strand
The discontinuous strand is called the lagging strand
Is first synthesized as short Okazaki fragments before becoming one strand
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20. Addition of DNA Nucleotides
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21. Leading Strand vs. Lagging Strand
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22. Enzymes of DNA Replication
Helicase
Unzips DNA double-helix
Topoisomerases
Prevents tangling and knotting of DNA as the while the strands are unzipped.
RNA primase
Initiates the formation of “daughter” strands
Forms a segment known as the RNA primer
The RNA primer contains the nitrogenous base Uracil
DNA Polymerase III
Enzyme that catalyzes the polymerization (making) of nucleotides
Adds Deoxyribonucleotides (nucleotides only found in DNA, as opposed to RNA) to the 3’ end of a growing nucleotide chain
Acts at the replication fork
DNA Polymerase I
A type of DNA polymerase will change the RNA primers into DNA
Changing the base Uracil into Thymine
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23. Enzymes of DNA Replication
DNA Ligase
Enzyme responsible for joining Okazaki fragments forming the Lagging Strand
Gyrase
Returns the DNA strands into a Double Helix
Zips the DNA back together
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24. DNA Replication—Lagging Strand
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25. DNA Replication—The Big Picture
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26. DNA Excision Repair DNA Polymerase II
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27. DNA Shortening
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28. Telomeres & Telomerase
End of eukaryotic chromosomes are known as telomeres
Short, non-coding, repetitive DNA sequences
Shorten each cell cycle but can be extended using the enzyme telomerase
Absence of telomerase in certain cells may be the cause of cell aging
Cells using their ability to divide after a limited number of cell divisions
Most cancer cells have telomerase to maintain the telomeres and possibly resist apoptosis.
Tuesday, November 13, 2018