1. The Molecular Basis of Inheritance
Campbell Biology – Chapter 16

2. DNA Structure and Replication
Cell
Nucleus
Deoxyribose
Nucleic
Acid
Chromosomes
DNA

3. DNA
It’s Unique:
Only molecule found in nature to direct its own replication.
Directs the
development of:
Biochemical
Anatomical
Physiological
Behavioral

4. Search for genetic material:
Why most scientists thought it was protein?
Great heterogeneity, specificity
Little known about nucleic acids
Chromosomes consist of:
DNA
Protein

5. Evidence of DNA transformation

6. change of phenotype due to assimilation of external stimuli
pathogenic
non-pathogenic
Transformation:
change of phenotype due to
assimilation of external stimuli

7. Avery, McCarty, MacLeod
Purified DNA from the heat-killed “S” cells and they transformed “R” cells.
Scientists still believe protein is the hereditary material? Why?
Know a lot about it.
Biochemical control (enzymes)
Lots of variation (20 amino acids)

8. More Evidence for DNA: Hershey and Chase

10. Additional Evidence for DNA
In eukaryotes (like you):
Mitosis – DNA is doubled
Diploid cells have 2X the DNA as haploid
Chargaff’s Rules (see #3)
Species Specific: ratios of bases vary from species to species
Adenine = Thymine
Guanine = Cytosine

11. James Watson and Francis Crick:
Discovered the structure
of DNA in 1953.
Discussed
probable mode of replication.

12. Phosphate, Sugar and a Base Cytosine Without Guanine
DNA Song
We Love DNA
Made of Nucleotides
Phosphate, Sugar and a Base
Bonded Down One Side
Adenine and Thymine
Make a Lovely Pair
Cytosine Without Guanine
Would Feel Very Bare

13. What’s a Nucleotide?
Phosphate
Base
Sugar

14. DNA includes 4 nitrogenous bases:
Adenine pairs
with Thymine
Pyrimidines
Purines
Guanine pairs
with Cytosine

15. DNA is double stranded:
Hydrogen bond connects
the base pairs.
Double Helix

16. DNA Model P G A T P S A S P S C P S T P

17. D = Deoxyribose
Pentose
Sugar:
5 sides

18. DNA Replication

19. Complementary Strands Separate

20. Parent Strands Serve as Template

21. Nucleotides connected

22. 3 possible modes of replication:
15/15
14/14
3 possible modes of replication:

23. 1st Replication found 14.5 density: 15

24. 2nd replication found 14 and 14.5

25. DNA Replication:

26. Antiparallel Strands: Sugar-phophate backbones run in opposite directions.

27. DNA Polymerase can only work in a 5’ to 3’ direction.
“Glues” the Okazaki
fragments together.
DNA Polymerase
can only
work in a
5’ to 3’
direction.
Made continuously as the
strand unwinds.
Made in chunks and later
connected.

28. Primase is the enzyme that
joins the RNA nucleotides
to make the primer.
The primer is an RNA stretch
that jump starts replication.

31. Proofreading and Repairing