3. TedED

4. We study DNA for many reasons, e.g., its central importance to all life on Earth, medical benefits such as cures for diseases, better food crops.

5. DNA double helix Discovery of the DNA double helix A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928) B.Rosalind Franklin - X-ray photo of DNA. (1952) C.Watson and Crick - described the DNA molecule from Franklin’s X-ray. (1953) SEE p. 292-293

6. DNA had specific pairing between the nitrogen bases:DNA had specific pairing between the nitrogen bases: ADENINE – THYMINE CYTOSINE - GUANINE DNA was made of 2 long stands of nucleotides arranged in a specific way called the “Complementary Rule”DNA was made of 2 long stands of nucleotides arranged in a specific way called the “Complementary Rule”

7. Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

8. O O=P-O OPhosphate Group Group N Nitrogenous base (A, G, C, or T) (A, G, C, or T) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose)

9. One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. nucleotide

10. The backbone of the molecule is alternating phosphate and deoxyribose, a sugar, parts. The teeth are nitrogenous bases. phosphate deoxyribose bases

11. DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix.

12. P P P O O O 1 2 3 4 5 5 3 3 5 P P P O O O 1 2 3 4 5 5 3 5 3 G C TA

13. PURINES PURINES Adenine (A) 1.Adenine (A) Guanine (G) 2.Guanine (G) PYRIMIDINES PYRIMIDINES Thymine (T) 3.Thymine (T) Cytosine (C) 4.Cytosine (C) T or C A or G

14. Adenine Thymine Adenine must pair with Thymine GuanineCytosine Guanine must pair with Cytosine about the same Their amounts in a given DNA molecule will be about the same. G C TA

15. CG H-bonds T A

16. Different arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms. Different arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

17. The “code” of the chromosome is the SPECIFIC ORDER that bases occur. The “code” of the chromosome is the SPECIFIC ORDER that bases occur. A T C G T A T G C G G…

18. See p. 297