1. The Molecular Basis of Inheritance
Who are these two famous characters of science?

2. Searching for Genetic Material
Mendel (1865): Inheritance

3. Searching for Genetic Material
What are chromosomes made of?
T.H. Morgan (1910): genes linked on chromosomes
Chromosomes are made of DNA and proteins
DNA and proteins are the two candidates for the genetic material

4. Searching for Genetic Material
Griffith(1928): bacterial work- streptococcus pneumoniae

5. Searching for Genetic Material
Griffiths’ conclusion:
Transformation: change in genotype and phenotype due to assimilation of external substance (DNA) by a cell

6. Searching for Genetic Material
Avery and team(MacLeod and McCarty)(1944): transformation agent was DNA

7. Searching for Genetic Material
Hershey and Chase(1952): determine that DNA is the hereditary material and not proteins:

8. DNA Structure Chargaff(1950): Chargaff rules: A= T, C= G
found “peculiar regularity” in the ratios of nucleotide bases within a single species:
A = 30.3%
T = 30.3%
C= 19.9%
G = 19.5%
Chargaff rules: A= T, C= G

9. Watson & Crick(Wilkins, Franklin)(1953):
The Double Helix

10. The Double Helix: Basic Unit of Nucleic Acids = nucleotide
Sugar/ phosphate backbone
Nitrogen base

11. Sugar/phosphate backbone:
5 carbon sugar = ribose
Phosphate group
Phosphodiester bond

12. Nitrogenous bases:
In DNA there are four(make up the interior of the molecule):
Adenine
Thymine
Cytosine
Guanine
Two groups:
Purines: double ringed structures
Adenine and Guanine
Pyrimidines: single ringed structures
Thymine and Cytosine

13. Polynucleotide directionality:
5’ to 3’
5’ with the phosphate group
3’ with the –OH group

14. Double strands:
Inward facing nitrogen base will pair with their complementary base
A will pair with T (two H- bonds)
G will pair with G (three H- bonds)
A double ringed structure will always pair with a single ringed structure to maintain width.

16. Antiparallel:
DNA strands are oriented in the opposite directions

17. Other forces:
Van der Waals attractions play a role in holding the DNA molecule together

18. The Double Helix:

19. DNA Replication

20. Watson and Crick:
Proposed the semiconservative model of DNA replication:

21. Meselson & Stahl: semiconservative replication

22. Enzymes:
Helicase, DNA polymerase, Primase, DNA ligase Topoisomerase

23. http://highered. mcgraw- hill
hill.com/sites/ /student_view0/chapter3/a nimation__dna_replication__quiz_1_.html

24. 5. 2. 1. ?’ ?’ ?’ ?’ 4. 3.

25. Replication Origin: Sites where DNA replication begins
Prokaryotes: one origin
Replication proceeds in two directions
Humans: hundreds maybe thousands of origins

26. Replication bubbles and Replication Forks;
Replication bubble: unwinding and separation of the DNA strand
Replication fork: Y- shaped region at each end of the bubble

27. Strand elongation and directionality:
Elongation catalyzed by DNA polymerase
E. coli bacteria adds nucleotides at a rate of 500/sec
Humans add nucleotides at a rate of 50/sec
Nucleoside triphosphate:

28. Strand elongation and directionality
Antiparallel elonagation:
5’ – 3’ direction
Leading strand
Lagging strand
Okazaki fragments
E. coli fragments: nucleotides
Human fragments:

29. Primers: How many primers are needed for the leading strand?
How many primers are needed for the lagging strand?

30. DNA Replication Continued:
DNA replication ensures continuity of hereditary information:

31. DNA Replication continued:
1. Enzymes of DNA replication work as part of a large complex:
2. Replication process is probably a stationary process
DNA polymerase “reels- in” the parent DNA
Lagging strand may may be looped

32. Problems with replication:
Incorrectly paired nucleotides
Error rate: 1 out of every 100,000 base pairs
DNA polymerase proof reads each nucleotide
Incorrectly paired nucleotides are immediately removed and replaced
1 out of 10 billion

33. Problems with replication:
Mismatch pair:
Repaired by the action of nuclease(one of many different DNA repair enzymes)
Removes nucleotides damaged by chemicals or the environment

34. Problems with replication:
End replication repair:

35. Telomeres and Telomerase:
Telomeres= nucleotide sequences at the ends of the DNA molecule
Contain a repeated unit TTAGGG
Do not contain genes
No nucleotides added
Protects the molecule from the replication process
Triggers apoptosis
May contribute to the aging process

36. Telomerase:
Catalyzes the lengthening of the telomeres in eukaryotic germ cells