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3. 2 DNA Why do we study DNA? We study DNA for many reasons: its central importance to all life on Earth because it codes for all PROTEINS medical benefits such as cures for diseases, better agricultural crops.

4. 3 What are Nucleic Acids? Organic MACROMOLECULESOrganic MACROMOLECULES DNA.DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins in the cell.

5. 4 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

6. 5 DNA A nucleic acid is made of many MONOMERS joined together nucleotidesNucleic acids are made up of monomers/ subunits called nucleotides copyright cmassengale

7. 6 DNA Nucleotide made of:Nucleotide made of: Phosphate group 1.Phosphate group 5-carbon sugar 2.5-carbon sugar Nitrogenous base 3.Nitrogenous base copyright cmassengale

8. 7 DNA Nucleotide 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) O copyright cmassengale

9. 8 Pentose Sugar Carbons are numbered clockwise 1’ to 5’ CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose) copyright cmassengale

10. 9 DNA Stands for Deoxyribonucleic acid Structure of DNA is a DOUBLE HELIX (2 stranded spiral) copyright cmassengale

11. 10 DNA DEOXYRIBOSE Deoxy means without OXYGEN DEOXYRIBOSE – 5 carbon sugar of DNA copyright cmassengale

12. 11 DNA Structure Rosalind Franklin took diffraction x-ray photographs of DNA crystals In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays copyright cmassengale

13. 12 Rosalind Franklin copyright cmassengale

14. 13 Can DNA leave the nucleus? copyright cmassengale

15. 14 One Strand of DNA One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. nucleotide

16. 15 One Strand of DNA The backbone of the molecule is alternating phosphates and sugar The rungs are nitrogenous bases. phosphate deoxyribose bases

17. 16 DNA Double Helix Nitrogenous Base (A,T,G or C) “Rungs of ladder” “Legs of ladder” Phosphate & Sugar Backbone copyright cmassengale

18. 17 The Double Helix Molecule The DNA double helix has two strands twisted together.

19. 18 DNA 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 copyright cmassengale

20. 19 Four nitrogenous bases Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

21. 20 Two Kinds of Bases in DNA Pyrimidines are single ring bases.Pyrimidines are single ring bases. Purines are double ring bases.Purines are double ring bases. C C C C N N O N C C C C N N N N N C

22. 21 Nitrogenous Bases Double ring PURINESDouble ring PURINES Adenine (A) Guanine (G) Single ring PYRIMIDINESSingle ring PYRIMIDINES Thymine (T) Cytosine (C) T or C A or G copyright cmassengale

23. 22 Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms.Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

24. 23 Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms.Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

25. 24 Chargaff’s Rule Adenine ThymineAdenine must pair with Thymine Guanine CytosineGuanine must pair with Cytosine The bases form weak hydrogen bonds G C TA copyright cmassengale

26. 25 Base-Pairings Purines only pair with Pyrimidines Three hydrogen bonds required to bond Guanine & Cytosine CG 3 H-bonds copyright cmassengale

27. 26 T A Two hydrogen bonds are required to bond Adenine & Thymine copyright cmassengale

28. 27 Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases but why do they stick together?

29. 28 C C C C N N O N C C C C N N O N N N C Hydrogen Bonds The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. The bonds between cytosine and guanine are shown here with dotted lines

30. 29 Hydrogen Bonds, Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine Adenine always pairs up with thymine Adenine is bonded to thymine here C C C C N N N N N C C C C C N N O O C