1. How do we know it’s our genetic material?
DNA
How do we know it’s our genetic material?

2. Several Experiments Science is not linear Many tests were done
Some right
Some wrong
Eventually we came to know about what DNA does

3. But, what factor in the nucleus controls all of the actions?
The Nucleus was the key
a series of experiments with algae showed that the nucleus controlled the actions of the cell
But, what factor in the nucleus controls all of the actions?

4. Griffith’s Experiment (1928)
experiments with Streptococcus (bacteria)
bacteria does not have a “nucleus”
genetic material floats around cytoplasm
two types of this bacteria

5. TYPE 1- Smooth (S)
S (smooth) has protective capsule
causes pneumonia in mice= mice die

6. TYPE 2- Rough (R)
R (rough) has no capsule
does not cause pneumonia in mice

7. S type is heat killed

8. S is heat killed and mixed with R

9. Findings dead bacteria could not come back to life
somehow, the R absorbed the information from the S and became like S type ( it was transformed)
There is some kind of controlling factor in the S type that makes it cause pneumonia

10. Avery and Colleagues(1944)
Knew chromosomes were made of DNA and proteins
expanded Griffith’s experiments to find out which one was the genetic material

11. Mixed Heat killed S and R with DNA destroying enzymes
Mixed heat killed S (harmful) and R (harmless) with protein killing enzymes
Results- R became deadly (R was Transformed)
Mixed Heat killed S and R with DNA destroying enzymes
Results- No Transformation- mice weren’t harmed
DNA must be genetic material but………many people were still skeptical

12. Hershey and Chase (1952) supported Avery’s findings
experimented with viruses
discovered that viruses could use bacterial DNA to replicate more viruses
Knew bacteria infecting viruses (bacteriophages) were made of protein and DNA

13. Hershey and Chase used radioactive labeling to identify the DNA and protein coats of viruses. Viral DNA injected into bacterium will direct the production of viruses, using bacterial DNA.

14. The bursting of a cell is
called Lysis
The protein coat of the viruses remained outside the bacterium, but the bacterium produced new viruses. The viruses contained the radioactive DNA.

15. Also first to identify the actual material as DNA using radioactive tracers
Concluded that DNA was the actual control molecule FINALLY!

16. Discovery of Structure
Erwin Chargaff (1949) – determined base pairing
Rosalind Franklin (50’s) -discovered DNA was a double helix
Watson and Crick (50’s)- created first model

17. THE DOUBLE HELIX

19. DNA STRUCTURE DNA is composed of a 3 part unit called a NUCLEOTIDE
-5 carbon sugar = DEOXYRIBOSE
-PHOSPHATE
-NITROGEN BASE (1 OF 4) NB S P NB NB S S P P NB NB S S

20. Bonds that hold DNA together
Sugar (Deoxyribose)-Phosphate = Covalent
Sugar (Deoxyribose)-Nitrogen Base=Covalent
Nitrogen Base(1 strand)-Nitrogen Base (2nd Strand)= Hydrogen Bond

21. NITROGEN BASES PURINES PYRIMIDINES ADENINE (A) GUANINE (G)
CYTOSINE (C)
THYMINE (T)
Large, double rings
Small, single rings

23. CHARGAFF’S RULE When forming the “rungs” of the “ladder”..
A always bonds with T
A is “complementary” to T
2 Hydrogen bonds hold them together
C always bonds with G
C is “complementary” to G
3 Hydrogen bonds hold them together
there will always be equal numbers of A and T; and of C and G

24. THINK ABOUT IT!
EVERY LIVING THING ON THIS PLANET IS COMPOSED OF ONLY 4 NITROGEN BASES. THE ONLY DIFFERENCE IS THE SEQUENCE OF AND NUMBER OF BASES

25. DNA REPLICATION
in order for a cell to duplicate, DNA must make a copy of itself
the process is called
DNA REPLICATION
an identical strand of DNA is produced

26. DNA unzips
Happens before the cell divides(mitosis), the whole strand unzips
An enzyme HELICASE does the unzipping
Many enzymes are involved in the rest of the process

27. DNA POLYMERASE does this
free nucleotides in the nucleoplasm(material in the nucleus) attach to the unzipped strands
DNA POLYMERASE does this

28. the “backbone” of sugars and phosphates will bond
two, identical, complete strands will form
each has half of the original