1. Deoxyribonucleic Acid Chapter 12 Section 1
DNA
Deoxyribonucleic Acid
Chapter 12 Section 1

2. Discovery of the Genetic Material
Scientists knew genetic information was carried on the chromosomes in eukaryotic cells, but where on the chromosome was unknown
Main parts of chromosomes: DNA and proteins
Major Contributors:
Griffith
Avery
Hershey and Chase
Chargaff
Watson and Crick

3. Frederick Griffith- 1928
First main discovery of DNA as genetic material
Working with Streptococcus pneumoniae he discovered that one strain could be transformed: Smooth and Rough strains
Smooth killed the host (mouse)
Heat smooth strain- host lived
Rough did not kill the host
Mixture of heated smooth and rough- hostdied

4. Extracted bacteria and made a culture:
-smooth trait appeared
Observation:
-the disease causing factor was passed from the killed S to the live R cells
Conclusion:
-bacteria transformed

5. Oswald Avery- 1944
Avery and colleagues identified the molecule that transformed the R strain into the S strain- not widely accepted
Isolated macromolecules (DNA, proteins, lipids) from killed S cells
Exposed live R cells to them
The exposure to the S strain DNA, macromolecules transformed into S cells
Conclusion: In Griffith’s experiment when S cells were killed, they released DNA and the R cells incorporated it into their cells, changing the bacteria into S cells.

6. Alfred Hershey and Martha Chase- 1952
Provided evidence that DNA indeed was the transforming factor
Used bacteriophage made of DNA and protein (virus that attacks bacteria)
Viruses cannot replicate themselves, they have to inject DNA into living material into a cell to reproduce
Radioactive labeled the bacteriophage to see which part was injected into the bacteria
Confirmed the DNA was the genetic material

7. Bacteriophage manipulation:
32P used to make DNA radioactive b/c proteins do not contain phosphorous
35S used to identify proteins b/c DNA does not contain sulfur
Result: viral DNA was injected into the cell and provided genetic information needed to produce NEW viruses
Conclusion: DNA is the genetic material passes from generation to generation in visues

8. DNA
Structure & Function

9. Humans share 50% of their DNA with bananas.
Cells can contain 6-9 feet of DNA. If all the DNA in your body was put end to end, it would reach to the sun and back over 600 times.
DNA in all humans is 99.9 percent identical. It is about one tenth of one percent that makes us all unique, or about 3 million nucleotides difference.
In an average meal, you eat approximately 55,000,000 cells or between 63,000 to 93,000 miles of DNA.
It would take a person typing 60 words per minute, eight hours a day, around 50 years to type the human genome.

10. ANIMATION
But, what is DNA?
P.A. Levene (1920’s)- Determined DNA is made up of 2 chains of nucleotides
Each nucleotide has 3 parts:
Deoxyribose sugar
Phosphate group
Nitrogenous base (1 of 4)
Adenine (A) -PURINE
Guanine (G) -PURINE
Cytosine (C) -PYRIMIDINE
Thymine (T) -PYRIMIDINE
VIDEO

11. Erwin Chargaff- 1950
Analyzed the amounts of nitrogenous bases found in DNA
Conclusion: the amount of adenine nearly is the same as the amount of thymine and the same for guanine and cytosine.
Thus: CHARGAFF’S RULE C=G and T=A

12. What does DNA look like? Franklin & Wilkins
Via the use of x-ray diffraction, Rosalind Franklin and Maurice Wilkins’ photo and data helped James Watson and Francis Crick, solve the structure of DNA.
Rosalind Franklin’s Photo 51

13. DNA Structure WATSON & CRICK
DNA is a double helix structure formed of 2 complementary precisely paired strands of nucleotides twisted around each other.

14. DNA Structure- Cont’d Base Pairing
Watson and Crick’s (1953) contributions
2 outside strands consist of alternating deoxyribose and phosphate “backbone”
cytosine and guanine bases pair to each other by 3 hydrogen bonds “rung”
thymine and adenine base pair to each other by 2 hydrogen bonds “rung”

15. Functions of DNA

16. Functions of DNA
DNA directs the machinery of a cell to make specific proteins, and, therefore, DNA indirectly controls all of the functioning of all living things.

17. Functions of DNA
2. DNA stores the hereditary information of an individual

18. Functions of DNA
3. DNA has the ability to mutate (change). This allows for new characteristics and abilities to appear which may help an individual to survive and reproduce (EVOLUTION).

19. Functions of DNA
4. Self replication: DNA has the ability to make copies of itself

20. Chromosomes and DNA
Recall: Prokaryotes the DNA is in the cytoplasm and in eukaryotes DNA is organized into chromosomes.
Human chromosome= million base pairs
DNA coils around proteins called histones (negative phosphate group attracts to histone to form a nucleosome)
Nucleosome group into chromatin fibers which supercoil to make up DNA structure we know as a chromosome

21. If all organisms are made of the same 4 nucleotides in their DNA, how are they so different?
Every organism has a different DNA sequence, which provides different information
The more closely related 2 organisms are, the more similar their DNA nucleotide sequences will be.

22. DNA Replication
Chapter 12 Section 2
Animation

23. When a cell divides, how does the DNA get copied?
Remember that DNA gets copied during the S phase of interphase prior to mitosis or meiosis.
This process is called DNA replication.
Semiconservative replication: parental strands of DNA separate, serve as templates and produce DNA molecules that have 2 strands.

24. Semiconservative Replication
3 stages
unwinding- hydrogen bonds between nitrogenous bases “unzipped” by the enzyme DNA helicase at the replication fork, RNA primer added to each strand of DNA
base pairing- enzyme DNA polymerase adds nucleotides to the 3’ end of the new DNA strand (A T and C  G)
joining- nucleotides bond together and DNA polymerases are released when they finish replicating the DNA & DNA ligase binds the pieces of DNA together
RESULTS: 2 separate and identical DNA molecules, each containing an original strand and a new strand of DNA.

25. What is with the 5’ and 3’?
It is just the position of the functional group on the 5 ring carbon…

26. DNA Replication Animation
Adds new DNA nucleotides
5’ to 3’
single stranded binding proteins keep helix apart
synthesized fragments
Replication Fork
connects fragments
Separates double helix
needed to start replication on 5’ end of lagging strand
3’ to 5’

27. Steps of Replication Summary
1) DNA strands pulled apart by rep. fork
2) SSBs bind to keep strands apart
3) RNA primase adds RNA primer
4) DNA polymerase adds DNA nucleotides primer
5) RNA primer removed
6) Gaps filled in by DNA polymerase
7) DNA ligase joins Okazaki fragments

28. How does DNA get copied so quickly?
Replication begins at thousands of points along a DNA molecule in eukaryotes, requiring thousands of helicases & DNA polymerases
In prokaryotes, the chromosome is circular, so replication begins at one site and proceeds in opposite directions until the entire molecule is copied.

29. How accurate is DNA replication?
If a mistake is made, DNA polymerase normally fixes it.
There is only about 1 error per billion nucleotide pairs.
Any error in DNA replication is called a mutation and it can have serious consequences, some good and some bad.

30.
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Complete p. 287 #1-6

31. Question to Ponder
We know what dominant and recessive mean, but what actually makes one trait dominant over another trait?

32. Here’s the brief answer:
The gene that produces the dominant trait contains information to make a functional protein.
The gene that produces the recessive trait contains information to make a non-functional protein.
In a codominant situation, the genes have the information for two different functional proteins.