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3. 2 DNA-Deoxyribonucleic Acid DNA.DNA is often called the ____________. In simple terms, DNA contains the ______ for making ______ within the cell.

4. DNA is like a fingerprint because everyone ’ s is a little different! How would the police look at DNA to figure out who committed a crime? You can tell people apart by their fingerprints……… and their DNA!

5. 4 Watson & Crick’s Model

6. 5 DNA Why do we study DNA? 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.

7. 6 Chromosomes and DNA Our _____ are on our _______. Chromosomes are _____________ _____________ _____________.

8. 7 The Shape of the Molecule DNA is a very long polymer. The basic shape is like a _____________. This is called a _______________.

9. 8 The Double Helix Molecule The DNA double helix has ______ strands twisted together.

10. 9 One Strand of DNA The backbone of the molecule is alternating ________ and ____________ The teeth are _____________ ____________. phosphate deoxyribose bases

11. 10 Nucleotides CC C O Phosphate O C C O -P O O O O O O O One deoxyribose together with its phosphate and base make a nucleotide. Nitrogenous base Deoxyribose

12. 11 One Strand of DNA One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. nucleotide

13. 12 Four nitrogenous bases _________ C _________ T _________ A _________ G DNA has four different bases:

14. 13 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

15. 14 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

16. 15 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

17. 16 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?

18. 17 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 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

19. 18 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

20. 19 Chargraff’s Rule: Adenine and Thymine always join together _________ Cytosine and Guanine always join together _________

21. 20 DNA by the Numbers Each cell has about _________ of DNA. The average human has _________. The average human has enough DNA to go from the earth to the sun _________ times. DNA has a diameter of only 0.000000002 m. The earth is 150 billion m or 93 million miles from the sun.

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