1. DNA

2. Let’s talk about it… 1. Can we see DNA with the naked eye? ** no
2. What evidence supports the presence of DNA?
**offspring look like their parents
3. Would every cell in a particular org. have the same DNA?
**yes, except sex cells
4. Why are sex cells an exception?
**23+23 =46, the number has to be haploid
5. Why must replication of DNA be accurate?
**so all cells have the same genetic information

3. What is DNA? DNA stands for.. D: Deoxyribose N: Nucleic A : Acid
DNA contains the genetic information that ultimately determines an organism’s traits.
Found in the chromosomes of ALL living things, including bacteria, viruses, mushrooms, pine trees, and zebras!

4. Why is it important? Everything that is living contains proteins.
All actions that we do, such as eating, running, and even thinking, depends on proteins called enzymes.
Your DNA determines the structure of these enzymes.

5. Alfred Hershey and Martha Chase
Who discovered it?
Alfred Hershey and Martha Chase

6. Who discovered it?
Alfred Hershey and Martha Chase – in 1952, performed an experiment using radioactive viruses that infect bacteria.
These viruses were made of only protein and DNA.
They saw that it was the DNA, that entered the cells and caused the bacteria to produce new viruses.

8. Rosalind Franklin

9. Rosalind Franklin
The first scientist to ever take a "picture" of the DNA molecule using X-rays. She saw that..
1) DNA molecule was long and thin, and;
2) helical and twisted.

10. Watson and Crick

11. James Watson and Francis Crick
1953: Watson and Crick
Proposed that DNA is made of two chains of nucleotides held together by nitrogenous bases.
It is shaped like a long zipper that is twisted into a coil like a spring, looks like a twisted ladder. They called it a double helix.

12. Watson and Crick

13. Chain #2
Nitrogenous bases
Chain #1

14. Components of DNA
DNA is made of repeating subunits called nucleotides.
Nucleotides have three parts:
1. A nitrogenous base
2. A deoxyribose sugar
3. A phosphate group.

15. A Nucleotide
Phosphate group
Nitrogenous base
Sugar (deoxyribose)

16. Four Nitrogenous Bases
In DNA, there are four different nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
Adenine (A)
Cytosine (C)
Thymine (T)
Guanine (G)

17. Simplified

18. Components of DNA
Nucleotides with different bases, are strung together in chains
Chains are held together by hydrogen bonds between the bases
Attached chains form a twisted ladder, in the shape of a double helix.
The phosphates and sugars make up the “backbone” of the molecule and the bases stick out like prongs of a zipper.

19. Chain #2
Nitrogenous bases
Hydrogen
bonds
Chain #1

21. Chargoff’s Rule
For each strand, there is a complimentary strand with matching base pairs.
The amount of adenine is always equal to the amount of thymine
The amount of guanine is always equal to the amount of cytosine.
Adenine ALWAYS bonds with Thymine
Cytosine ALWAYS bonds with Guanine

22. On the strands.. A=T (double bond) C≡G (triple bond) “A” = Adenine
“T” = Thymine
“C” = Cytosine
“G” = Guanine
A=T (double bond)
C≡G (triple bond)

23. Example of Base-Pairing
Example strand of DNA
(Find each complimentary base pair for the strand of DNA)
A—C—T—A—G—A—C—C—T—A—G—T
| | | | | | | | | | | |
T—G—A—T—C—T—G—G—A—T—C—A

24. Life on earth
All organisms, from bacteria to humans are made up of the same bases, just in a different order.

25. The DNA Song!!! To the tune of Row, Row, Row Your Boat… We Love DNA
Made of Nucleotides!
Sugar, phosphate, and a base
Bonded down one side.
Adenine and thymine
Make a lovely pair!
Cytosine without guanine
Would feel very bare!

26. Discussion… 1. What happens during interphase?
**cell growth and replication of DNA
2. Does this happen before or after a cell divides?
**before
3. Why does it happen this way?
**daughter cells get the same # and type of chromosomes
4. What is replication or what does it mean?
**to make copies or duplicates of DNA
5. What is the shape of DNA?
**double helix
6. How can we get a molecule shaped like this to copy itself?
**untwist and unzip

27. DNA Replication
Replication is during interphase so each new daughter cell has the same information before mitosis.
The DNA in the chromosomes is copied in a process called DNA replication.
Replication results in two strands of DNA IDENTICAL to the original.
Each strand serves as a template for the new one.
Without DNA replication, new cells would have only half the DNA of their parents

28. Steps of Replication
1. Enzymes break the H+ bonds, holding the bases together.
2. The DNA molecule “unzips” and new nucleotides are attached by their base pair to each original strand.
3. Results in two identical DNA molecules, each has one strand from the original and one new.

29. *Honors*
DNA has the ability to duplicate or make copies of itself. 1. to replicate, strands must be untwisted and unzipped. (hydrogen bonds broken) 2. replicating DNA is called a "replicating fork," each strand is a template (pattern) 3. DNA polymerase allows free nucleotides to bond to open strands (A to T & C to G) 4. DNA polymerase only works 5' to 3', adding to 3' 5. 5' to 3' strand is the leading strand replicated constantly, 3' to 5' is lagging strand 6. lagging strand has to be constructed away from fork in Okazaki fragments (1968) 7. DNA ligase joins the fragments 8. end with 2 strands of DNA, each with 1 old and 1 new strand (semi-conservative)

30. DNA Replication

32. Original DNA molecule
New strand (red)
Original strand (blue)
New strand (red)
New strand (red)
Original strand (blue)
Original strand
(red)

33. Example of DNA Replication
(Unzip the following strand of DNA, and write the two strands of DNA that would result from the replication)
C—G—T—C—A—T—C—G—C—A—A—T—G
| | | | | | | | | | | | |
G—C—A—G—T—A—G—C—G—T—T—A—C 
Strand #1
C—G—T—C—A—T—C—G—C—A—A—T—G
| | | | | | | | | | | | |
G—C—A—G—T—A—G—C—G—T—T—A—C
Strand #2
C—G—T—C—A—T—C—G—C—A—A—T—G
| | | | | | | | | | | | |
G—C—A—G—T—A—G—C—G—T—T—A—C

34. Sooo, DNA is a CODE! 1. What is a code?
**symbols used to store info. (ex. *Morse, computers, DNA, alphabet )
2. How is DNA a code?
**it stores genetic information (traits, cell function)
We’ll talk more about what this Code does next time