1. The Molecular Basis of Inheritance13
The Molecular Basis of Inheritance

2. ??????? Genetic Material ???????
? What is It?
? Where is It?
? How is it used?
? Who ANSWERED these Questions??

3. Most RECOGNIZEABLE Names and Contribution!
Figure 13.1 How was the structure of DNA determined? 3

4. DNA DOUBLE HELIX STRUCTURE!
On April 25th of 1953, James ________and Francis ________ introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA
BUT……. What came BEFORE and What has come AFTER??????
First Question? What is the Genetic Material??? Sec 13.1:
? ________________ or ?_________________ 4

5. The Search for the Genetic Material: Scientific Inquiry
When T. H. Morgan’s group showed that genes are located on chromosomes (CH 12), the two components of chromosomes—DNA and protein—became candidates for the genetic material
The key factor in determining the genetic material was choosing appropriate experimental organisms – MO’s!!!
What were the TWO KEY MO’s Used??? 5

6. GRIFFITH’s Unexpected Experiment!!!
The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928
Original Experiment Goal?
MO? 6

7. Griffith’s Experiment – View CyberEd Video Clips #16,17,&18 On CH13 Wiki Link
Notes:

8. Experiment Mixture of heat-killed S cells and living R cells Living
Figure 13.2
Experiment
Mixture of
heat-killed
S cells and
living R cells
Living
S cells
(control)
Living
R cells
(control)
Heat-killed
S cells
(control)
Figure 13.2 Inquiry: Can a genetic trait be transferred between different bacterial strains?
Results
Mouse dies
Mouse healthy
Mouse healthy
Mouse dies
Living S cells 8

9. Griffith’s Conclusion and the NEXT STEP!
Next GOAL – Identify this _________________ Agent!!! Who?? _______________________ How??
(view CyberEd)
Problem: 9

10. Hershey & Chase:
Hypo:
MO: 10

11. To Reproduce = Phage Attach to a Bacteria Host and
INJECTS HEREDITARY MATERIAL!
???????

12. Phage head Tail sheath Tail fiber DNA 100 nm Bacterial cell
Figure Visual Proof! Hindsight is 20/20 – T2 Phage Lytic Cycle or Repro! View Video of T2 Lytic Cycle
Phage
head
Tail
sheath
Tail fiber
DNA
Figure 13.3 Viruses infecting a bacterial cell
100 nm
Bacterial
cell 12

13. 2 STOCK Cultures of Radioactive Phage: 1 –
2 –
Not?? 13

14. View CyberEd 22,23,&24 – also on wiki!
Plus CH14 on the “Biology 8th Edition Raven Site found on the B2H Main Page on the Wiki!
Notes:

15. Batch 1: Radioactive sulfur (35S) in phage protein
Figure 13.4
Experiment
Batch 1: Radioactive sulfur (35S) in phage protein 1
Labeled phages
infect cells. 2
Agitation frees outside
phage parts from cells. 3
Centrifuged cells
form a pellet.
Radioactive
protein 4
Radioactivity
(phage protein)
found in liquid
Centrifuge
Pellet
Batch 2: Radioactive phosphorus (32P) in phage DNA
Radioactive
DNA
Figure 13.4 Inquiry: Is protein or DNA the genetic material of phage T2?
Centrifuge 4
Radioactivity (phage
DNA) found in pellet
Pellet 15

16. H&C Conclusion:

17. Additional Evidence That DNA Is the Genetic Material – History of DNA Experimentation:
1869 – Miescher Discovered DNA by Extraction from Human WBC’s! View CyberEd (not on wiki)
1920’s - P.A. Levene and Colleagues Discover Basic Monomer Structure / Components of DNA and RNA! 17

18. 5 end Nitrogenous bases Sugar– phosphate Thymine (T) backbone
Figure 13.5
5 end
Nitrogenous bases
Sugar–
phosphate
backbone
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
3 end
DNA
nucleotide

19. Levene (continued): View CyberEd (not on wiki)

20. In 1950, Erwin Chargaff reported that DNA composition varies from one species to the next!
Data Table with %’s: (Make Observations!)

21. Chargaff:
All 4 Nucleotides are NOT in Equal Proportions of 1:1:1:1
IF they WERE, %’s would show ____:____:____:____
CONC: DNA is NOT as Simple as 1st Thought and COULD BE the Genetic Material!!!
HOW? Analyzed N-Base Composition/%’s in Many Different Organisms
Ex. Human:

22. CHARGAFF’S RULES:
Key: Still DID NOT Know the STRUCTURE of DNA!!! These Rules will help CONFIRM DNA Structure!

23. Scientific Skills Exercise: Page 249
Figure 13.UN01
Scientific Skills Exercise: Page 249
Figure 13.UN01 Skills exercise: working with data in a table 23

24. GC Content / GC Richness????? FYI!!!! Wikipedia!
GC ratio of genomes[edit]
GC ratios within a genome is found to be markedly variable. These variations in GC ratio within the genomes of more complex organisms result in a mosaic-like formation with islet regions called isochores.[10] This results in the variations in staining intensity in the chromosomes.[11] GC-rich isochores include in them many protein coding genes, and thus determination of ratio of these specific regions contributes in mapping gene-rich regions of the genome.[12][13]
GC ratios and coding sequence[edit]
Within a long region of genomic sequence, genes are often characterised by having a higher GC-content in contrast to the background GC-content for the entire genome. Evidence of GC ratio with that of length of the coding region of a gene has shown that the length of the coding sequence is directly proportional to higher G+C content.[14] This has been pointed to the fact that the stop codon has a bias towards A and T nucleotides, and, thus, the shorter the sequence the higher the AT bias.[15]

25. Building a Structural Model of DNA:
James Watson and Francis Crick were first to determine the structure of DNA
Maurice Wilkins and Rosalind Franklin were using a technique called X-ray crystallography to study molecular structure
Franklin produced a picture of the DNA molecule using this technique
READ ARTICLE on Drama between WCWF: Link is on CH13 Page on Wiki! 25

26. Figure 13.6
(a) Rosalind Franklin
(b) Franklin’s X-ray diffraction
photograph of DNA
Figure 13.6 Rosalind Franklin and her X-ray diffraction photo of DNA
View CyberEd of Technique! NOTE: Wilkins’s contribution was PURIFYING the DNA into a Fiber to be used in the X-Ray Diffraction Technique. 26

27. Watson and Crick’s Model: Book Pages 249 and 250
Key Components: 27

28. Thinking through the Structure!!!
DNA HANDSHAKE!!!! 28

29. (b) Partial chemical structure (c) Space-filling model
Figure 13.7
5 end C G C G
Hydrogen bond
3 end G C G C T A
3.4 nm T A G C G C C G A T
1 nm C G T A C G G C C G A T
Figure 13.7 The double helix A T
3 end A T
0.34 nm T A
5 end
(a) Key features of
DNA structure
(b) Partial chemical structure
(c) Space-filling
model 29

30. Concept 13.2: Many proteins work together in DNA replication and repair
The relationship between structure and function is manifest in the double helix
Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material
1st = Look at BASIC Mechanism: PG 252/253
2nd = Look at SPECIFICS – Rest of 13.2 30

31. Meselson and Stahl’s Experiment to ID How DNA undergoes the Replication Process:
Watson and Crick had an idea of how, but needed Experimental Proof!!
M&S 3 Hypotheses: (Build Each with Pipecleaners)
1) ___________________ = 31

32. 2) ___________________ =
3) ____________________ =

33. First replication Second replication
Figure 13.10
First
replication
Second
replication
Parent cell
(a) Conservative
model
(b) Semiconservative
model
Figure Three alternative models of DNA replication
(c) Dispersive
model 33

34. M&S Experimental Design:
MO: _______________ Why?
View CyberEd of Experiment – Also on CH13 Wiki Page!

36. Bacteria cultured in medium with 15N (heavy isotope) Bacteria
Figure 13.11a
Experiment 1
Bacteria
cultured in
medium
with 15N
(heavy
isotope) 2
Bacteria
transferred
to medium
with 14N
(lighter
isotope)
Results
Less
dense 3
DNA sample
centrifuged
after first
replication 4
DNA sample
centrifuged
after second
replication
Figure 13.11a Inquiry: Does DNA replication follow the conservative, semiconservative, or dispersive model? (part 1: experiment and results)
More
dense 36

37. Conclusion Predictions: First replication Second replication
Figure 13.11b
Conclusion
Predictions:
First replication
Second replication
Conservative
model
Semiconservative
model
Figure 13.11b Inquiry: Does DNA replication follow the conservative, semiconservative, or dispersive model? (part 2: conclusions)
Dispersive
model 37

38. DNA Replication: A Closer Look
The copying of DNA is remarkable in its speed and accuracy
More than a dozen enzymes and other proteins participate in DNA replication
Much more is known about how this “replication machine” works in bacteria than in eukaryotes
Most of the process is similar between prokaryotes and eukaryotes
SWITCH to ADDITIONAL NOTEPACKET on DNA REPLICATION!!!!! 38

39. DNA pol III Parental DNA Leading strand 5 5 3 3 3 5 3 5
Figure 13.18
DNA pol III
Parental DNA
Leading strand 5 5 3 3 3 5 3 5
Connecting
proteins
Helicase
Lagging
strand
template 3 5
Figure A current model of the DNA replication complex
DNA
pol III
Lagging strand 3 5 39

40. Proofreading and Repairing DNA
DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides:
_____ Subunit of DNAPIII! PG 257
_____ = Initial Error Rate vs _____ = End Error Rate
(100,000 lower error rate due to Proofreading!)
Second Chance??? ________________________
(Not just from Replication Error, but After due to chemical and physical agents in the Environment)
Humans = 130 ID’ed E.coli = ~100 ID’ed 40

41. A DNA Polymerase and Ligase Complete Repair!
Figure 5 3
PG 258: Nucleotide excision repair, a nuclease cuts out damaged stretches of DNA
Damage Caused by UV-Rays – Adjacent T’s covalently link and cause buckle!
A DNA Polymerase and Ligase Complete Repair! 3 5
Nuclease 5 3 3 5
DNA
polymerase 5 3
Figure Nucleotide excision repair of DNA damage (step 3) 3 5
DNA ligase 5 3 3 5 41

42. Evolutionary Significance of Altered DNA Nucleotides
Error rate after proofreading repair is low but not zero
Sequence changes may become permanent and can be passed on to the next generation
These changes (mutations) are the source of the genetic variation upon which natural selection operates – KEY: Mutation must occur in __________ cells to pass on to NEXT Generation!
NOTE Most are _____________ BUT a small percentage can be ______________!!!!! 42

43. Replicating the Ends of DNA Molecules
Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes
The usual replication machinery cannot complete the 5 ends of daughter strands - Repeated rounds of replication produce shorter DNA molecules with uneven ends
SOLUTION???? ________________________ 43

44. What Other Cells have this Enzyme?
Figure 13.20
Do NOT Prevent errosion, but Postpone! – Shortening is thought to play are part in AGING or LIMITING # of CELL ÷’s
What ABOUT Germline Cells? How Can they have so MANY Divisions without Losing Telomeres/Erroding?
What Other Cells have this Enzyme?
Figure Telomeres
1 m 44

45. Concept 13.3: A chromosome consists of a DNA molecule packed together with proteins
BACTERIAL Chromosomes / Prokaryotic Cells:
________________ = form allows for Protection and eliminates need for ______________ so endless rounds of binary fission!
Very few __________________ for spooling!
Located in the ____________________ of the cytoplasm!
Refer to Page 259 for other facts!! 45

46. EUKARYOTIC Chromosomes: ________________ = Need for ______________!
________________ = Complex of DNA and Multiple Proteins
Linear Chromosomes are dynamic structures that condense, loosen, modify, and remodel for various cell processes: mitosis, meiosis, and gene activity! See Book Pages Fig 13.21
View Video: 46

47. Replicated chromosome (1,400 nm)
Figure 13.21
Chromatid
(700 nm)
Nucleosome
(10 nm in diameter)
DNA
double helix
(2 nm in diameter)
30-nm
fiber
Loops
Scaffold H1
300-nm
fiber
Histone tail
Histones
Figure Exploring chromatin packing in a eukaryotic chromosome
Replicated chromosome
(1,400 nm) 47

48. At interphase, most of the chromatin is compacted into a 30-nm fiber, which is folded further in some areas by looping
Even during interphase, centromeres and some other parts of chromosomes are highly condensed, similar to metaphase chromosomes
This condensed chromatin is called heterochromatin; the more dispersed, less compacted chromatin is called euchromatin 48

49. Dense packing of the heterochromatin makes it largely inaccessible to the machinery responsible for transcribing genetic information
Chromosomes are dynamic in structure; a condensed region may be loosened or modified as needed for various cell processes
For example, histones can undergo chemical modifications that result in changes in chromatin organization 49