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Aim:

Aim:. Do Now:. Why must DNA copy itself?. What are some key characteristics of DNA?. Homework:. Castle Learning Assignment #6. Review. What are the four different bases of DNA? Which bases pair up together? What are the substances that make up the back bone of DNA?

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  1. Aim: Do Now: • Why must DNA copy itself? • What are some key characteristics of DNA? Homework: • Castle Learning Assignment #6

  2. Review • What are the four different bases of DNA? • Which bases pair up together? • What are the substances that make up the back bone of DNA? • What bonds hold the two strands of DNA together? • What is the shape of a DNA molecule? • What could a chromosome be described as?

  3. Why does DNA need to be copied? • Genetic information in DNA must be copied exactly and passed on from parent cell to daughter cells • Daughter cells must have the same number of chromosomes (46) as the parent cell (46) • Remember those sister chromatids?

  4. “The Great Understatement” • In their famous paper in 1953 that describes DNA’s structure, Watson and Crick write: • "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." • This quote is called “The Great Understatement” because it hints at how the molecule of life has been copying itself starting with the first cell 5 billion yrs ago

  5. How did studying this model tell Crick and Watson how DNA replicated?

  6. Replicate your DNA • On a slip of paper, write down the sequence of bases – the code -that your piece has (this is the “parent molecule”) • Use the materials provided to figure out how to go from one parent molecule to two IDENTICAL daughter molecules • Compare the code in your daughter molecules to the original code in the parent molecule…how’d you do?

  7. Steps to DNA replication • An enzyme called helicase unwinds the DNA helix • Another enzyme “unzips”, or breaks, the hydrogen bonds that hold the bases together, revealing 2 single strands • These single strands are called “templates” • An enzyme called DNA polymerase attaches new nucleotides to the two templates, following the base pairing rules: • Adenine bonds to Thymine • Cytosine bonds to Guanine • The result are 2 new double stranded pieces of DNA, identical to the original parent strand

  8. Closure • Make a flow map that explains the steps in DNA replication • These must be shown and checked off before the end of the period

  9. Aim: What are some of the key parts of DNAreplication? Do Now: Fill out the printed flow chart. Homework: Text Book Pg 336 – 341 Questions 1-5 on Pg 341

  10. DNA Replication

  11. An In-depth look at DNA replication • DNA replication begins during interphase of the cell cycle • When DNA helicase unwinds the DNA the hydrogen bonds are broken separating the two strands. • Another enzyme appears called RNA primase which adds a short section of RNA to each DNA strand.

  12. DNA Helicase

  13. What is the function of DNA polymerase? • Next the DNA polymerase comes through and attaches the different nucleotides. • This reads the 3 prime end of the DNA. • There are two separate names for the strands of DNA • Leading strand and lagging strand • The leading strand is put together continuously.

  14. DNA Leading and Lagging Strand

  15. What is the difference between the leading and lagging strand? • The lagging strand is put together in pieces. • The small sections are referred to as okazaki fragments 100 – 200 base pairs long. • These fragments are later joined together using an enzyme called DNA ligase (glue)

  16. DNA Replication

  17. Exit Slip • What is the function of DNA Helicase? • Why is DNA ligase so important? • What is the difference between the leading strand and the lagging strand? • Why are hydrogen bonds so important to this? • Where does DNA replication take place?

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