1. DNA

2. What is the major component of all cells?
PROTEINS

3. Why would protein synthesis be important?
cellular structures
enzymes
cell membrane structures
organelles
direct all other cellular activities

4. What substance directs protein synthesis?
DNA

5. molecule responsible for all cell activities
DNA
molecule responsible for all cell activities
and contains the genetic code
Genetic Code
method cells use to store the program that is passed from one generation to another

6. DISCOVERY OF THE GENETIC CODE
1928: Frederick Griffith
(studied how bacteria cause pneumonia)

7. Griffith Experiment 1 1. Grew 2 strains of bacteria on plates
- smooth colonies- caused disease (virulent)
- rough edge colonies-did not
cause disease (avirulent)
2. Injected into mice
Results:
- smooth colonies: died
- rought colonies: lived
Conclusion:
bacteria didn’t produce a toxin to kill mice

8. Griffith Experiment 2
Injected mice with heat killed virulent strain
Injected mice with
non -virulent strain + heat killed virulent strain
Results:
- heat killed: lived
- mixed strains: mice developed pneumonia
Conclusion:
heat killed virulent strain passed disease causing abilities to non virulent strain

9. Cultured bacteria from dead mice and they grew virulent strain.
After Experiment
Cultured bacteria from dead mice and they grew virulent strain.
Griffith hypothesized that a factor was transferred from heat killed cells
to live cells .
TRANSFORMATION

10. DNA was transforming factor
1944: Avery (et al)
1. Repeated Griffith’s experiment with same results.
- result: transformation occurred
2. Did a second experiment using enzymes that would
destroy RNA.
3. Did third experiment using enzymes that would destroy DNA.
- result: no transformation
CONCLUSION
DNA was transforming factor

11. Virus composed of DNA core and protein coat
1952: Hershey / Chase
- studied how viruses (bacteriophage) affect bacteria.
Bacteriophage
Virus composed of DNA core and protein coat

12. How Bacteriophages Work
1. bacteriophage attaches to surface of bacteria and injects DNA
2. bacteria makes phage DNA
3. bacterial cell bursts
4. sends out new phages to infect more bacteria
animation

13. Hershey Chase Experiment
1. They labeled virus protein coat with radioactive sulfur
2. They labeled virus DNA with radioactive phosphorous
Result
observed that bacteria had
phosphorous
*** virus injected bacterial cells with its phosphorous labeled DNA***
Conclusion
DNA carried genetic code
since bacteria made new
DNA.

14. DISCOVERY OF STRUCTURE OF DNA

15. Maurice Wilkins: x ray diffraction, worked with Franklin
Early 1950’s: Rosalind Franklin (English)
x ray evidence:
X pattern showed that fibers of DNA twisted and molecules are spaced at regular intevals on length fiber.
Maurice Wilkins: x ray diffraction, worked with Franklin

16. 1950’s Watson (American) & Crick (English)
**double helix model**
won Nobel prize in 1962

17. DNA A – T - may have 1000’s of nucleotides in 1 strand
- double strand of nucleotides
- may have 1000’s of nucleotides in 1 strand
(very long molecule)
- bases join up in specific (complementary) pairs:
complementary pairs (base pairing rules)
1 purine bonds with 1 pyrimidine on one rung of the ladder connected by a weak H bond
C - G
A – T
Order of nucleotides not important,
proper complementary bases must be paired.

18. Chargaff (American biochemist)
Same time period:
Chargaff (American biochemist)
Chargaff’s Rule:

19. STRUCTURE OF DNA Composed of: A. Phosphate B. Deoxyribose sugar (5 C)
C. 4 Nitrogenous bases
- Purines Adenine A
Guanine G
- Pyrimidines Thymine T
Cytosine C
D bases attached to sugar
E. bases attached to each other by weak H bond

20. Nucleotide Structure
Purines Pyrimidines
Sugar
Base
Phosphate

21. REPLICATION OF DNA Process of duplication of DNA
Before cell can divide a new copy of DNA
must be made for the new cell
- Semiconservative replication:
each strand acts as a template (pattern) for new strand to be made
End Result:
one old strand, one new daughter strand

22. DNA REPLICATION

23. Models of DNA Replication

24. Steps of Replication
1. Enzyme DNA helicase attaches to DNA molecule and unwinds 2 strands at various points on the strand
(breaks H bonds so strand unwinds)
- replication forks: two areas on either end of the DNA where double helix separates
- forms replication bubble: “bubble” under electron microscope

25. 2. Enzyme DNA polymerase moves along each of DNA strand and adds complementary bases of nucleotides floating freely in nucleus
A. DNA polymerase begins synthesis at RNA primer segment
- enzyme RNA Primase lays down this section on DNA strand
- RNA primer segment signals beginning of replication

26. DNA Directionality

27. - directionality: DNA polymerase reads the template in the 3’ to 5’ direction
Daughter DNA strand (since it is complementary) must be synthesized in the 5’ to 3’ direction
Strands are antiparallel.

28. But if there exist no DNA polymerases
capable of polymerizing DNA in the
3' to 5' direction, how could this be?

29. Discontinuous synthesis
- synthesis only occurs when a
large amount of single strand
DNA is present
- daughter DNA is then synthesized in 5’ to 3’ direction
- leading and lagging strands:
- leading strand – continuously synthesized DNA strand - lagging strand - delayed, fragmented, daughter DNA
- Okazaki fragments discontinuous fragmented DNA segments

30. D. DNA ligase stitches
together Okazaki
fragments into a
single, unfragmented
daughter molecule
E. enzyme chops off
RNA primer and
replaces it with DNA

31. Once all DNA is copied, daughter DNA detaches
DNA polymerase catalyzes formation of H bonds between nucleotides of template and newly arriving nucleotides which will form daughter DNA
Once all DNA is copied, daughter DNA detaches
animation

32. End Replication Problem
On one end, RNA primer cannot be replaced with DNA because it is a 5’
(DNA polymerase can only read from 3’ to 5’)
Causes daughter DNA’s to be shorter with each
replication (cell division)
3’__________________________________ 5’
5’ ’
5’__________________________________ 3
3’ ’

33. Solution to End Replication Problem
telomeres: regions of repeated non coding sequences at end of chromosomes (protective sacrificial ends)
- become shorter with repeated cell divisions
- once telomeres are gone, coding sections of chrom are lost and cell does not have enough DNA to function
***telomere theory of aging***
- telomerase: special enzyme that contains an RNA template molecule so that telomeres can be added back on to DNA
(rebuilds telomeres)
** found in:
Cancer cells - immortal in culture
Stem cells
** not found in most differentiated cells

34. Speed of Replication
Multiple replication forks- replication occurs simultaneously on many points of the DNA molecule
Would take 16 days to replicate 1 strand from one end to the other on a fruit fly DNA without multiple forks
Actually takes ~ 3 minutes / sites replicate at one time
Human chromosome replicated in about 8 hours with multiple replication forks working together
                                                                                                                                                                                 

35. Accuracy and Repair Cell has proofreading functions
DNA polymerase can remove damaged nucleotides and replace with new ones for accurate replication
RNA does not have this ability- reason RNA viruses
mutate so much
DNA damaged by heat, radiation, chemicals and other factors

36. RNA (Ribonucleic acid)
Importance of DNA
Controls formation of all substances in the cell by the genetic code
Directs the synthesis of specific strands of m RNA to make proteins
RNA (Ribonucleic acid)
Another nucleic acid takes orders from DNA Used in protein synthesis