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The Structure & Replication of DNA

The Structure & Replication of DNA. History of Discovery. F. Griffith discovered a “transforming principle” within cells that directed their activity O. Avery suggested that DNA was the “transforming principle” A. Hershey & M. Chase confirmed that DNA was the genetic material of a cell

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The Structure & Replication of DNA

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  1. The Structure & Replicationof DNA

  2. History of Discovery • F. Griffith discovered a “transforming principle” within cells that directed their activity • O. Avery suggested that DNA was the “transforming principle” • A. Hershey & M. Chase confirmed that DNA was the genetic material of a cell • J. Watson & F. Crick created the first accurate model of DNA

  3. DNA is Made of … • Nucleotides • Sugar (deoxyribose) + phosphate + base • Adenine • Thymine • Guanine • Cytosine • Joined by dehydration reaction • OH (hydroxyl) required

  4. DNA Shape • Double-helix • Like a spiral staircase

  5. How DNA is Built • DNA has two halves held together by hydrogen bonds • Hydrogen bonds are between base pairs • Adenine and Thymine (2 hydrogen bonds) • Guanine and Cytosine (3 hydrogen bonds) • Two strands are anti-parallel • They run in opposite • directions • Each half is complimentary • to the other half

  6. DNA Replication • Watson & Crick came up with the semi-conservative replication model • When DNA is copied, each daughter strand has half original DNA and half new DNA

  7. Details of DNA Replication • Many enzymes are involved with DNA replication, including: • Helicase • Primase • DNA Polymerase III • DNA Polymerase I • Each enzyme has a specific job to do in the process

  8. Questions to Consider … Write these down in your science notebook, along with your answers. • What is the function of each enzyme involved in DNA replication? • What are the steps to DNA replication? • What is required for DNA Polymerase III to begin construction of new DNA? • How does replication of the leading strand differ from that of the lagging strand? • Is the leading strand always the leading strand? Explain. • Where – and why – does a primer-sized gap remain unfilled at the end of replication? • If a gap remains unfilled each time DNA replicates, predict what will eventually happen to a chromosome?

  9. OH P P OH 1. Helicase unwinds and unzips the parent DNA molecule.

  10. OH P primase OH P P OH P OH primase 2. Primase uses RNA (ribonucleic acid) nucleotides to create primers. The primers provide a hydroxyl (OH) for DNA to be built upon.

  11. OH OH OH P P P DNA Polymerase III DNA Polymerase III OH P P P P OH OH OH P OH primase primase primase primase LEADING STRAND LAGGING STRAND 3. DNA Polymerase III can now add DNA nucleotides to the hydroxyl. 4. Primers are repeatedly added to the lagging strand which is replicated in segments in the opposite direction of replication. LAGGING STRAND LEADING STRAND

  12. OH OH OH P P P OH P P P P OH OH OH P OH DNA Polymerase I DNA Polymerase I DNA Polymerase I DNA Polymerase I DNA Polymerase I DNA Polymerase I P OH OH P 5. DNA Polymerase I now removes the RNA primers and fills in the gap left by them using DNA nucleotides. 6. On the phosphate (P) end of each daughter strand, a primer-sized gap remains unfilled.

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