1. DNA STRUCTURE AND REPLICATION
CHAPTER

2. What is DNA? composed of? Proteins and DNA
Hereditary material present in all living cells
Composed of monomers called nucleotides
Is part of the chromosomes
What are chromosomes
composed of? Proteins and
DNA
Before ~ 1940 people did not
really know what the genetic
material was

3. Nucleic Acids Elements C, H, O, N, P Monomers: Nucleotides
Polymers: Nucleic acids
Examples: DNA, RNA, ATP.
Deoxyribonucleic acid
Ribonucleic acid
Adenosine triphosphate

4. Monomer - nucleotide DNA -adenine, guanine, cytosine and THYMINE
Nucleotide consists of
Ribose sugar (deoxy in DNA)
Phosphate group
One of 5 nitrogenous bases
DNA -adenine, guanine, cytosine and THYMINE
RNA adenine, guanine, cytosine and URACIL

5. DNA is a double helix A sugar and phosphate
“backbone” connects nucleotides in a chain. P T P A 3’ 5’ 5’ 3’ P C P G
A pairs with T and
G pairs with C P C P G
Two nucleotide chains
together wind into a helix. P T P A
Hydrogen bonds between
paired bases hold the two
DNA strands together. G P P C P C P G
DNA strands are antiparallel.

6. A history of DNA Friedrich Miescher, 1871 isolated nuclei from pus and
identified nuclein later called nucleic acid.
what is pus?
Archibald Garrod, 1902
linked inheritance of “inborn errors of metabolism” with the lack of particular enzyme proteins.
Shows that something must be passed on from parent to offspring

7. WHICH IS MORE LIKELY TO BE GENETIC MATERIAL?
Protein
DNA

8. FREDERICK GRIFFITH’S EXPERIMENTS in 1928
Worked with two types of pneumonia causing bacteria:
S-strain covered by a capsule and causes pneumonia and death of mice
R-strain had no capsule and does not cause pneumonia
Mice were injected with the bacteria to see if they contracted pneumonia

9. Griffith’s experiment identifying the “transforming principle”
Bacterial
colonies
Rough
nonvirulent
(strain R) +
Rough
nonvirulent
(strain R)
Heat-killed
smooth
virulent
(strain S)
Smooth
virulent
(strain S)
Heat-killed
smooth
virulent
(strain S)
Injection
Results
Mouse healthy
Mouse healthy
Mouse dies
Mouse dies
Live strain S bacteria
in blood sample
from dead mouse

10. FREDERICK GRIFFITH’S RESULTS
R bacteria (safe) mixed with heat-killed S bacteria (capsule still present) killed the mouse
Griffith’s discovery: TRANSFORMATION, Something (presumably the hereditary material) from the heat killed S bacteria transferred to the safe R bacteria and changed its genetic composition to give pneumonia

11. AVERY et al’s EXPERIMENT
Repeated Griffith’s experiments, utilizing enzymes to destroy DNA, RNA, and protein, respectively
Protease to destroys all proteins
DNAse to destroys all DNA

12. What is the “transforming principle”?
Conclusion: DNA could be the genetic material.

13. HERSHEY-CHASE EXPERIMENT in 1953
When a virus infects a bacteria, it produces more viral particles which are identical to the parent virus. So ….
Virus composed of Protein and DNA
STEP 1: Viral proteins and DNA “marked” with two different radioactive elements
S35 for proteins – coats radioactive
P32 for DNA – genetic material radioactive

14. Experiment 1
Experiment 2

15. HERSHEY-CHASE EXPERIMENT
Conclusion: Examined infected bacteria
Found radioactive DNA inside the bacteria
Radioactive proteins – outside the bacteria
Nobel Prize!

16. Chargaff’s Experiment
Erwin Chargaff observed:
# of adenine = # of thymine
# of guanine = # of cytosine
Complementary bases pair:
A and T pair
C and G pair

17. Rosalind Franklin’s Experiment
Rosalind Franklin’s X-ray images
Conclusion: Repeating double helix structure
Franklin (died in 1958 of cancer) did not get the Nobel Prize in 1962

18. WATSON AND CRICK: “THE DOUBLE HELIX”

19. DNA Structure DNA made up of two twisted strands
Adenine pairs w/Thymine
Cytosine pairs w/Guanine
Two strands held together by weak hydrogen bonds
The sugar and phosphate make the backbone (or sides of ladder)of the molecule
Nitrogen bases make the middle or (rungs of ladder)

20. WHAT IS THE COMPLEMENTARY STRAND?
A C G C C A G T A

21. WHAT IS THE COMPLEMENTARY STRAND?
A C G C C A G T A
T G C G G T C A T

22. What is the role of the genetic material and what is a gene?
The genetics material has to be able to carry out two jobs
Faithfully duplicate itself to transfer the same genetic information to daughter cells during cell division
Express itself and make proteins for the cell to carry out it duties
A gene is a segment of the DNA containing an unique sequence of bases that directs the formation of an unique protein which will do the cellular work

23. REPLICATION OF DNA

24. DNA REPLICATION REPLICATION: Process by which DNA is copied
When during the cell cycle is the DNA copied?
Result: Each new cell contains a complete, exact copy of DNA of the parent cell

25. STEPS IN DNA REPLICATION
Helix unwinds and unzips making Y-shaped “replication forks”
Replication fork

26. STEPS IN DNA REPLICATION
Nucleotides base pair with the parent DNA strands
Attach with H bonds
A-T, G-C
DNA Polymerase makes the covalent bonds to join the backbone

27. STEPS IN REPLICATION
Two new identical helixes form each with one parent strand and one daughter strand
Semi-conservative replication