1. Ch. 12 DNA and RNA What kind of DNA do clones have? Xeroxyribonucleic Acid What kind of DNA do joggers have? Reeboxyribonucleic Acid What do diarrhea and DNA have in common? They both run in the jeans(genes)!

2. REVIEW QUESTIONS What organelle is known as the “control center” of the cell? Nucleus What can be found in the nucleus? DNA, Chromosomes What are chromosomes made of? DNA How do genes and chromosomes control the activity of a cell?

3. 12-1 DNA Pg. 287

6. The Components and Structure of DNA Scientists discovered that genes were made of DNA. They wondered how DNA could do the 3 critical things that genes were known to do: 1. Genes had to carry info from one generation to the next. 2. Genes put information to work by determining the inheritable characteristics of an organism. 3. Genes have to be easily copied because genes are replicated every time a cell divides

7. For DNA to do all of that, it would have to be a very SPECIAL molecule!

8. DNA is a long molecule made up of units called nucleotides. The 3 basic components of a nucleotide are: 5-carbon sugar (deoxyribose) Phosphate Group Nitrogenous Base The Components and Structure of DNA

9. The Nucleotide 3 individual nucleotides separated The nitrogenous Base The sugar molecule The phosphate group

10. The Bases Phosphate group Deoxyribose Nitrogenous Base

12. En Espanol

13. The Components and Structure of DNA There are four kinds of nitrogenous bases: Adenine (A) Guanine (G) Cytosine (C) Thymine (T) The backbone of a DNA chain is formed by sugar and phosphate groups of each nucleotide.

14. The Bases Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose Nitrogenous Base

15. Backbone of DNA

16. Structure of DNA Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

17. Chargaff’s Rules Erwin Chargaff discovered that the percentages(%) of G’s and C’s are almost equal in any sample of DNA. The same is true for the other two nucleotides, A’s and T’s. A=T and C=G became known as Chargaff’s rules. No one had any idea why this was!

18. Chargaff's Rules

19. X-ray Evidence In the early 1950’s Rosalind Franklin began to study DNA. She used a technique called X-ray diffraction to get information about the structure of the DNA molecule. She discovered that DNA was a double helix.

20. Franklin X-shaped DNA (from X-ray Diffraction

21. The Double Helix Two scientists, Watson and Crick, were trying to understand the structure of DNA by building 3-D models of the molecule. Once given Franklin’s results, they discovered the actual structure of DNA and made a model of it. Watson and Crick’s model of DNA was a double helix, in which two strands were wound around each other. A double helix looks like a twisted ladder or a spiral staircase.

25. Double Helix Twisted Ladder or Spiral staircase = Double Helix

26. They discovered that hydrogen bonds could form between certain nitrogenous bases and provide just enough force to hold the two strands together.

27. Structure of DNA Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

28. Hydrogen bonds can form ONLY between certain base pairs: Adenine and thymine Cytosine and guanine They called this principle, base pairing. **Now there was a reason that A=T and G=C!

30. Structure of DNA Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

31. 3 ways to view DNA