1. How is DNA duplicated in the Synthesis Stage?
DNA Replication
How is DNA duplicated in the Synthesis Stage?

2. Discovery of the Genetic Material
Griffith – studied the bacteria that causes pneumonia in mice; this disease-causing factor could be passed between two strains of bacteria
Avery – using the same type of cells as Griffith, broke the strains down to the component macromolecules to determine nucleic acids (DNA) were responsible for the transformation
Hershey and Chase – confirmed DNA was the transforming factor by using radioactive labeling in viruses

3. DNA Structure Levene – basic structure of nucleotides Sugars
Five carbon sugar, phosphate group, and nitrogenous base
Many nucleotides compose a nucleic acid (DNA or RNA)
Sugars
DNA – deoxyribose (one less oxygen)
RNA – ribose
Nitrogenous Bases
Guanine (G) and adenine (A) – double rings (purine)
Thymine (T) and cytosine (C) – single rings (pyrimidine)

4. Deoxyribonucleic Acid

6. Chargaff’s Rule Amount of A = T and amount of C = G which means…
Chromosome consists of million base pairs
Only 5 centimeters long...how does it fit?
Tightly coils around histones
DNA + histone = nucleosome
They’re paired!
5th Period stopped here

7. Wilkins, Franklin, Watson, and Crick
Photo 51 via x-ray diffraction
Double helix/twisted ladder
Controversies in science
DNA Structure
Two outside strands containing an alternating phosphate and sugar
Cytosine and Guanine paired together by three hydrogen bonds
Thymine and adenine paired together by two hydrogen bonds
Aiming x-rays at the DNA molecule
Why 3 v. 2?

8. We’ll talk about these numbers 3 and 5 later…
Hydrogen bonds!

9. So that’s the Structure, how is it replicated?
Semiconservative replication – one strand serves as a template (Watson and Crick)

10. The Process Unwinding – DNA Helicase Orientation – 3’ and 5’ ends
Replication fork
Hydrogen bonds are broken
RNA Primase follows behind to add an RNA primer
Orientation – 3’ and 5’ ends
These are enzymes
RNA Primer – serves at the starting point for DNA polymerases
Note how the 3 and 5 are at opposite ends for each of the strands…

11. New Old The process (cont.)
DNA Polymerase adds the appropriately paired nucleotides to the template DNA strand
The template strand is read from the 3’ to the 5’ end
The new strand is created in the 5’ to the 3’ orientation antiparallel to the original one
Old
New

12. Leading and Lagging Strands
Because the template strand is always read from the 3’ to the 5’ end, it is “easier” for DNA polymerase to replicate one of the template strands (leading strand).
Okazaki Fragments result in the lagging strand

13. Conclusion
DNA replication occurs in many places on the chromosome at once
Another DNA polymerase comes through and replaces the RNA Primers with nucleotides
DNA Ligase links the many fragments of DNA
Including the Okazaki fragments
Prokaryotic replication – one origin of replication (DNA is called a plasmid)
Transformation – bacteria extracts DNA from an outside source