1. Ch. 16: The Molecular Basis of Inheritance
…the nature of DNA

2. Evidence that DNA is the genetic material
Griffith’s Experiment
Streptococcus pneumoniae
Molecules has the ability to change phenotype of various cells. (bacteria)
= Transformation

3. Griffith’s Experiment

4. … more evidence that DNA is the genetic material
Evidence that Viral DNA can program cells
Hershey-Chase Experiment
T4 phage and E.coli
Either protein coat OR DNA will infect cell
Tagged coat and DNA with radioactive markers
Showed that the nucleic acid inside virus is transmitted to host cell

5. Hershey-Chase Experiment

6. DNA Structure
DNA is a Double Helix - like a twisted rubber ladder made from three main components (like legos)
Sides of the ladder are composed of alternating sugar and phosphate pieces
Each “rung” of the ladder is made up of two complementary bases
A bound to T
C bound to G
DNA is put together in chunks called NUCLEOTIDES
Each nucleotide has a sugar, PO43- and base

7. Purines and Pyrimidines
Nucleotide
Purine

8. DNA Structure Double Helix Chargaff: Rosalind Franklin Watson/Crick
%G = %C
Rosalind Franklin
X Ray Chromatography
Shape
Width
Spacing b/w nucleotides
Watson/Crick
Built Model of DNA using info above
Determined bonding of A-T and G-C

9. DNA Replication Possibilities

10. Replication #1 DNA Helicase comes on the scene UNWINDS the DNA
UNZIPS the DNA
This site is known as the replication bubble

11. Replication #2
Complementary Bases begin adding into both sides of the ds DNA
Needs DNA Polymerase Enzyme
A binds with T, C binds with G (no other possibility because of the shape of the bases!)
The DNA Polymerase precedes the paired bases and clips out any that are already added ahead of it (on the 3’ end) with an exonuclease activity

12. Replication #3 Finally you have 2 identical copies of ds DNA
The final job of the Polymerase is to Proofread the NTP’s after they are added (back on the 5’ end) and to clip out any that are incorrectly paired
DNA Ligase fuses backbone of DNA

13. DNA Replication and Repair
Base pairing, semiconservative
Necessary enzymes
Helicases
DNA polymerases
DNA ligase
Make new DNA in a 5´3´ direction
Needs a Primer for DNA Polymerase to attach to DNA
Proof-reading and repair of damage
mismatch repair
excision repair

14. Priming DNA Synthesis

15. Two Strands of DNA are AntiParallel
Sugar phosphate backbone run in opposite direction.
Each strand has a 3’ and 5’ end
New strand of DNA can ONLY be made in 5’  3’direction OR
Follows old DNA in 3’  5’ direction
Leading strand
Lagging Strand

16. Lagging Edge also forms from 5’ to 3’. Forms Okazaki Fragments.
Leading Edge of DNA Replication
New strand forms 5’ to 3’ continuously
Lagging Edge also forms from 5’ to 3’.
Forms Okazaki Fragments.
DNA Replication Review

17. Difficulty in ends of DNA

18. Difficulty in ends of DNA
Telomeres: Section of nucleotide sequence containing no genes
Telomerase: enzyme that catalyzes lengthening of DNA
May have factors in determining life span
May be related to cancer

19. Telomeres/Telomerases