1. Frederick Griffith discovered in 1928 that a "rough" non-pathogenic strain of pneumonia bacteria could be transformed into a "smooth" pathogenic strain through exposure to heat-killed pathogenic bacteria. 2. Hershey and Chase provided evidence in 1952 that DNA, not protein, was the genetic material through experiments using radioactive labeling of bacteriophages. 3. Watson and Crick deduced the double-helix structure of DNA in 1953 based on Chargaff's rules of DNA composition and Rosalind Franklin's X-ray crystallography photos of DNA.

1. DNA and Genes
Chapter 10

3. Frederick Griffith
(1928)
• Studied pneumonia bacteria,
Streptococcus pneumoniae. It has
2 strains, “smooth” (S) and “rough” (R). These
traits were inherited by the bacterium.
• His studies of pneumonia bacteria showed that
"something" had caused the R strain to be
transformed into the S strain

5. Conclusion: Conclusion: Conclusion: Conclusion:
Encapsulated strain without Polysaccharide R strain cells
strain is polysaccharide coat did not had acquired
pathogenic is non- cause the ability to
pathogenic pneumonia make
polysaccharide
coats from the
dead S cells
and this trait
was inheritable

6. • This phenomenon is known as
transformation--change in phenotype due to
the assimilation of externally acquired
genetic material.
• From these experiments the nature of the
inheritable material could not be
determined.

7. • By the 1940's, it was understood that
chromosomes carry the heritable material.
• At this time little was known about DNA
other than it was fairly uniform and thought
to be uniform throughout.
• Proteins were thought to be not uniform
and to have a great deal of functional
specificity.
• For these reasons, many scientists thought
protein was likely to be the genetic
material.

8. Hershey & Chase
(1952)
• Studied bacteriophages
("bacteria eaters'' viruses
that infect bacteria), which
are composed of a DNA core
and a protein coat

9. Phage attaches Phage injects DNA. Phage DNA directs host
to bacterial cell. cell to make more phage
DNA and protein parts.
New phages assemble.
Cell lyses and
releases new phages.
• Bacteriophages attach themselves to the surface of a
bacterium and inject their DNA into the bacterium
• Phages were labeled with radioactive phosphorus to
detect DNA

10. • They had successfully used radioactive
labeling to provide evidence that DNA was
the transforming factor for Griffith’s work

11. Rosalind Franklin & Maurice Wilkins
(early 1950's)
• made X-ray crystallography photographs
of DNA to learn its structure

12. Erwin Chargaff (1950)
• An American biochemist
(1905-2002)
• He demonstrated 3 rules
about DNA structure

13. • Chargaff's Rules, which state that in DNA:
1.The number of adenine (A) residues always
equals the
number of thymine (T) residues
2.The number of guanine (G) residues always
equals the
number of cytosine (C) residues
3.The number of purines (A+G) always
equals the number of pyrimidines (T+C) —
this rule is an obvious consequence of rules
1 and 2.

14. • He also showed that these rules hold
true even though the ratio (G+C):(A+T)
varies from one type of organism to
another.
• Two years later he explained these
findings to James Watson and Francis
Crick.

15. Watson & Crick
1953
• Used Chargaff’s discoveries and Rosalind
Franklin’s X-ray crystallography pictures to
deduct the double-helix model of DNA.

16. Methods used to
observe DNA

17. Chromosome Smear – stain of the
chromosomes in a human cell:

18. KARYOTYPE
• Takes chromosomes from chromosome
smear and arrange them by size and
grouped into homologous pairs.
• Homologous chromosomes have genes
for the same traits arranged in the same
order

20. Predict what the
karyotype of a
normal male would
look like?

21. Genes
 a segment of DNA
on the chromosome
 responsible for the
production of one protein
 human cell contains 50,000 to
100,000 genes

22. Gene Mapping – tells what each segment (gene) of
the chromosome codes for.

23. Gel Electrophoresis – Mix
DNA with restriction
enzymes, which break the
DNA into fragments that are
then stained. Then put
fragments into a gel and
introduce electricity. The
DNA fragments are
separated according to size.

24. The Breakdown of DNA: The
Molecule of Heredity

25. Prokaryote DNA
• DNA in prokaryotes, such as bacteria, is
circular and called plasmids.
• There can be several plasmids inside the cell.
• The plasmids are accompanied by a single
chromosome located in the cytoplasm.

26. E. coli Bacteria

27. Eukaryote DNA
DNA is contained in the
chromosomes which are
located in the membrane-
bound nucleus.

28. Chromosomes are
composed of many,
many genes, which are
composed of long DNA
strands.

29. Chromosome Structure
of Eukaryotes
Chromosome Nucleosome
DNA
double
helix
Coils
Supercoils
Histones