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The Structure of DNA

The Structure of DNA. Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA. Chromosomes and DNA. DNA. DNA is “the blueprint of life” DNA contains the instructions for making proteins within the cell. What does DNA look like? Watson & Crick’s Model.

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The Structure of DNA

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  1. The Structure of DNA

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

  3. DNA • DNA is “the blueprint of life” • DNA contains the instructions for making proteins within the cell.

  4. What does DNA look like?Watson & Crick’s Model • Double Helix • Twisted Ladder

  5. Sugar (deoxyribose) Phosphate Group Nitrogenous Base Made of nucleotides:3 Components

  6. S S P P S S P P S S The two sides of the ladder The sugar and phosphate make the sides of the ladder

  7. The rungs are the bases

  8. There are 4 bases • Adenine Thymine • Guanine Cytosine • A always pairs with T (sticks) • C always pairs with G (curves)

  9. A T C A-T and C-G T A G

  10. A T C Complimentary Base Pairing T Hydrogen bonds hold bases together A G

  11. Why do we study DNA? • medical reasons • better food crops • forensics

  12. The earth is 150 billion m or 93 million miles from the sun. DNA by the Numbers • Each cell has about 2 m of DNA. • The average human has 75 trillion cells. • The average human has enough DNA to go from the earth to the sun more than 400 times. • DNA has a diameter of only 0.000000002 m.

  13. C T A G Chargaff’s Rule • Adeninemust pair with Thymine • Guanine must pair with Cytosine • Their amounts in a given DNA molecule will be about the same.

  14. Question: • If there is 30%Adenine, how much Cytosine is present?

  15. Question: • When and where does DNA Replication take place?

  16. S phase DNA replication takes place in the S phase. G1 G2 interphase Mitosis -prophase -metaphase -anaphase -telophase Synthesis Phase (S phase) • S phase in interphase of the cell cycle. • Nucleus of eukaryotes

  17. Replication • DNA copies itself before division • Steps: • Unwinds • Unzips • Copies using the old strands as templates • Uses complementary base pairing • Semiconservative: end up with one old strand and one new strand

  18. 3’ Parental DNA Molecule 5’ Replication Fork 3’ 5’ DNA Replication Replication Forks: hundreds of Y-shaped regions of replicating DNA molecules where new strands are growing.

  19. Bubbles Bubbles DNA Replication Replication Bubbles:

  20. DNA Template Parental DNA New DNA DNA Replication • Semiconservative Model: Old strands serve as templates New molecules have one old, one new strand

  21. Question: • What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’

  22. Answer: DNA 5’-GCGTATG-3’ DNA 3’-CGCATAC-5’

  23. You Try it! • http://www.pbs.org/wgbh/aso/tryit/dna/shockwave-nojs.html

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