1. DNA:(Deoxyribonucleic Acid) Aim: Why is DNA such an important molecule?

2. Genetic material of cells…
GENES – units of genetic material that CODE FOR A SPECIFIC TRAIT
DNA is made up of repeating molecules called NUCLEOTIDES

3. From cell to DNA… http://www.pbs.org/wgbh/nova/genome/dna.h tml#
(a quick animation showing the structure of genetic material)

4. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

5. The Discovery of DNA
Fredrich Mieshcer (1869) – the 1st scientist to isolate DNA
However… many scientists still thought PROTEINS carried genetic instructions

6. Frederick Griffith
Griffith was a bacteriologist who studied streptococcus pneumonia (the bacteria responsible for Strep throat and pneumonia)
He demonstrated the transformation of DNA from one bacteria to another
He called his discovery “The Transforming Principle”

7. Griffith’s Transformation Experiment

8. Griffith’s conclusion
Something from the heat-killed virulent bacteria (S-strain) must have been transformed (moved into) to the non- virulent bacteria (R strain) to make them disease-causing
However…. What caused the transformation – was it protein or DNA???

9. Avery, Macleod & McCarty - 1944
Wanted to determine the exact genetic material of a cell – what causes the transformation?
They used enzymes to destroy specific parts of the cell – ie lipids, proteins, DNA, carbohydrates, etc)
Transformation occurred in EVERY case EXCEPT tests with DNA-destroying enzymes

10. Conclusion??
DNA is the genetic material of cells and is responsible for transformations

11. Application for DNA transformation
Transformation experiments cause bacteria (E.coli) to “take up” a gene resistant to penicillin as well as a luminescent “green” gene from a jellyfish.

12. Hershey & Chase
In 1952, Alfred Hershey and Martha Chase used a new technology called radioactive labelling to show that genes are made of DNA
They were able to “label” DNA with radioactive phosphorus and watch it incorporate itself into bacterial cells
They also “labelled” protein with radioactive sulfur and found that the protein did NOT transform into the bacterial cells

13. The Hershey-Chase Experiment

14. The Hershey-Chase Experiment
hill.com/olc/dl/120076/bio21.swf

15. Phoebus Levene – discovery of nucleotides
Levene was a biochemist who discovered that DNA and RNA are made up of long chains of NUCLEOTIDES – of which there are 5 types.
DNA – adenine, thymine, cytosine, guanine
RNA – adenine, uracil, cytosine, guanine

16. Chargaff’s Rule Adenine pairs with Thymine Guanine pairs with Cytosine
Their amounts in a given DNA molecule will be about the same. T A G C

17. Relative proportions (%) of Bases in DNA of Several Organisms
A (adenine)
T (thymine)
G (guanine)
C (cytosine)
E. Coli
26.0
23.9
24.9
25.2
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Rat
28.6
28.4
21.4
21.5
Human
30.9
29.4
19.9
19.8

18. Rosalind Franklin – 1950s
Used x-ray photography to look “through” DNA molecules
She concluded that the nitrogenous bases (A,T,C,G) were located on the inside (the “rungs”) and the sugar-phosphate backbone was located on the outside
Her work was used by Watson & Crick in the discovery of the double helix model of DNA

19. Rosalind Franklin
She graduated from Cambridge University with a PhD in Chemistry
She also spent much of her short life studying molecular biology and x- ray crystallography
Sadly, she succumbed to ovarian cancer at 37.

20. James Watson & Frances Crick
James Watson and Frances Crick shared the Nobel Prize in 1962 for their discovery of the DNA double helix

21. Watson & Crick proposed…
DNA had specific pairing between the nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
DNA was made of 2 long stands of nucleotides arranged in a specific way called the “Complementary Rule”

22. DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone

23. DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

24. Nitrogenous Bases A or G T or C PURINES – 2 “rings” 1. Adenine (A)
2. Guanine (G)
PYRIMIDINES - 1 “ring”
3. Thymine (T)
4. Cytosine (C)
A or G
T or C

25. BASE-PAIRINGS C G
H-bonds T A

26. Fig

27. Genetic Diversity…
Different arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

28. The Code of Life… A T C G T A T G C G G…
The “code” of the chromosome is the SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…

29. DNA is wrapped tightly around histones and coiled tightly to form chromosomes

30. DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

31. DNA strands are ANTIPARALLEL5’ 3’ 3’ 5’
One of the DNA strands runs from 3’ to 5’ and the other runs in the opposite direction – 5’ to 3’

32. HISTORY OF DNA GRIFFITH’S EXPERIMENT AVERY, MACLEOD, McCARTY
HERSHEY-CHASE EXPERIMENT
CHARGAFF’S RULE
WATSON-CRICK (FRANKLIN)

34. Replication of DNA

35. DNA REPLICATION starts at the replication origin
DNA helicase “unzips” DNA double strand
DNA polymerase (enzyme) adds free nucleotides to the unravelled DNA strand
DNA polymerase can’t initiate a new DNA strand in a 5’ to 3’ direction – THEREFORE a short strand of RNA (called an RNA primer) serves as a starting point
HOWEVER – DNA polymerase can only attach
nucleotides to the 3’ end (old strand is 3’ to 5’ and new strand is 5’ to 3’)(LEADING STRAND)
Again, because DNA can’t initiate a new DNA strand, an RNA primer is laid down first
Because the DNA polymerase only attaches new DNA 3’ to 5’ – the replication is discontinuous and backwards
Short fragments called Okazaki fragments
form and DNA ligase “glues” them together
(this becomes the LAGGING
STRAND)

36. REPLICATION (DNA DNA)

37. DNA Replication
(McGraw-Hill animation)
(more detailed, complex explanation of DNA replication)

38. REPLICATION IN BACTERIA
Replication takes place at several locations simultaneously
Each replication bubble represents 2 replication forks moving in opposite directions along the chromosome
The bubbles continue to grow until they meet

39. Replication in Bacteria

40. Replication Questions
1. Why is replication necessary?
2. When does replication occur?
3. Describe how replication works.
4. Use the complementary rule to
create the complementary strand:
A---?
G---?
C---?
T---?

41. Replication Answers So both new cells will have the correct DNA A---T
1. Why is replication necessary?
So both new cells will have the correct DNA
2. When does replication occur?
During interphase (S phase).
3. Describe how replication works.
Enzymes unzip DNA and complementary nucleotides join each original strand.
4. Use the complementary rule to
create the complementary strand:
A---T
G---C
C---G
T---A

42. DNA Replication Semiconservative Model: .
1. Watson and Crick showed: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand. .
DNA Template
New DNA
Parental DNA

43. Semi-Conservative Nature of DNA Replication
meselsonstahl_meselson_.swf

44. (1961) Watson & Crick proposed…
…DNA controlled cell function by serving as a template for PROTEIN structure.
3 Nucleotides = a triplet or CODON
(which code for a specific AMINO ACID)
AMINO ACIDS are the building blocks of proteins.

45. Protein structure
For a cell to get the proteins it needs, it must translate the codons along a stretch of mRNA into amino acid sequences. At the ribosomes, tRNA carries a particular amino acid to the correct mRNA codon site.

46. Several amino acids are bonded together to form a polypeptide

47. THE CENTRAL DOGMA
DNA RNA PROTEIN