1. DNA: The Genetic Material Chapter 14

2. 2 DNA Structure DNA is a nucleic acid. The building blocks of DNA are nucleotides, each composed of: –a 5-carbon sugar called deoxyribose –a phosphate group (PO 4 ) –a nitrogenous base adenine, thymine, cytosine, guanine

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5. 5 DNA Structure Nucleotides are connected to each other to form a long chain The chain of nucleotides has a 5’ to 3’ orientation.

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7. 7 DNA Structure Determining the 3D structure of DNA involved these scientists: –Erwin Chargaff determined that amount of adenine = amount of thymine amount of cytosine = amount of guanine *Known as Chargaff’s Rules

8. 8 DNA Structure Rosalind Franklin and Maurice Wilkins –performed X-ray diffraction to identify the 3-D structure –discovered that DNA is helical

9. Rosalind Franklin’s X-ray Photo (1951)

10. 10 DNA Structure James Watson and Francis Crick, 1953 –discovred the structure of DNA using evidence from Chargaff, Franklin, and others –proposed a double helix structure

11. 11 DNA Structure The double helix consists of: –2 sugar-phosphate backbones –nitrogen bases face interior of molecule –bases form hydrogen bonds with complementary bases on the opposite sugar-phosphate backbone

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13. 13 DNA Structure The two strands of nucleotides are antiparallel to each other –one is oriented 5’ to 3’, the other 3’ to 5’ Strands wrap around each other to create the helical shape

14. 14 DNA

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16. 16 DNA Replication DNA replication includes: –initiation – replication begins at an origin of replication –elongation – new strands of DNA are synthesized by DNA polymerase –termination – replication is terminated

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18. 18 DNA Replication DNA replication is semidiscontinuous. –can only add nucleotides to the 3’ end of the newly synthesized strand –DNA strands are antiparallel to each other leading strand is synthesized continuously (in the same direction as the replication fork) lagging strand is synthesized discontinuously creating Okazaki fragments

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21. 21 DNA Repair Mistakes during DNA replication can lead to changes in the DNA sequence and DNA damage. DNA can also be damaged by chemical or physical agents called mutagens. Repair mechanisms may be used to correct these problems.

22. 22 DNA Repair DNA repair mechanisms can be: –specific – targeting a particular type of DNA damage photorepair of thymine dimers –non-specific – able to repair many different kinds of DNA damage excision repair to correct damaged or mismatched nitrogenous bases

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25. GENE