2. Review What organelle is the “control center” of the cell? The nucleus What structures are found in the nucleus? Chromosomes What structures are located on chromosomes? Genes What are chromosomes made of? DNA and protein

3. How? How do genes and chromosomes control the activity of a cell? By producing proteins that regulate cellular functions or become part of the cell.

4. Frederick Griffith – British Scientist In 1928 he wanted to find out how bacteria produced pneumonia, a serious lung disease. He isolated two types of pneumonia bacteria from mice. One type caused illness when injected into mice, one didn’t. Griffith heated the disease causing strain to kill the bacteria, and injected it into mice; it did no harm.

5. He then injected both the heat killed disease causing, and the non- disease causing strain into mice, and they got sick and died.

6. Conclusion Griffith hypothesized that some factor was transforming the harmless bacteria into the bad, harmful strain.

7. Oswald Avery – Canadian biologist In 1944, he treated an extract made from the heat- killed bacteria with enzymes, to kill proteins, lipids, RNA and other molecules. Transformation still occurred. He then used different enzymes to break down DNA, and this time transformation did not occur.

8. Conclusions Scientists concluded that DNA was the transforming factor, and that DNA is the material that stores, and transmits the genetic information from one generation to the next.

9. Hershey and Chase – American Scientists In 1952 they studied a bacteriophage which is a virus (non-living particles smaller than a cell) that infects bacteria. Bacteriophage means “bacteria eater”. They experimented and concluded that the genetic material of a bacteriophage is also DNA.

10. Components of DNA DNA is a long molecule made of units called nucleotides. Each nucleotide consists of: 1) A 5-carbon sugar called deoxyribose 2) A phosphate group 3) A nitrogenous base

11. Four kinds of Nitrogenous Bases 1. Adenine – a purine 2. Guanine – also a purine 3. Cytosine – a pyrimidine 4. Thymine – also a pyrimidine

12. Structure of DNA The “backbone consists of the sugar and phosphate. The bases stick out to the side. In 1953 Watson and Crick discovered that DNA was actually in the shape of a double helix, or “twisted ladder”. They found that hydrogen bonds could form between bases, and that base pairing occurred.

13. Base Pairing Means that in DNA: Adenine always pairs with Thymine Guanine always pairs with Cytosine

14. Review 1. What Three Components Make up a Nucleotide? ▪ Deoxyribose (a sugar) ▪ A Phosphate Group ▪ Nitrogenous Base

15. 2. What is a bacteriophage? A virus that eats bacteria. 3. What are the four nitrogenous bases? Adenine, Cytosine, Guanine, Thymine 4. What base does adenine pair with? Thymine 5. What base does cytosine pair with? Guanine

16. 6. What is the shape of DNA? A double helix, or “twisted ladder” 7. Who discovered the shape of DNA? Watson and Crick

17. True or False ? 8. DNA is a very long molecule of many nucleotides hooked together in a chain. True

18. DNA Replication Before a cell divides it must duplicate it’s DNA, so that each new daughter cell will have a complete set of DNA. This process is called replication. During replication, the DNA molecule separates into 2 strands, then produces two new complementary strands following the rules of base pairing.

19. How does it separate? Remember, the bonds that hold the bases together are weak hydrogen bonds. DNA polymerase is the main enzyme involved in replication.

20. DNA Replication Video http://www.youtube.com/watch?v=zdDkiRw1PdU