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NOTES: 12.2 – 12.3 DNA Structure & Replication

Explore the intricate structure of DNA, from its nucleotide composition to the double helix formation. Understand DNA replication process in prokaryotic and eukaryotic cells. Detailed insights on Chromatin, DNA polymerase, and enzymes involved in replication.

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NOTES: 12.2 – 12.3 DNA Structure & Replication

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  1. NOTES: 12.2 – 12.3DNA Structure & Replication

  2. 12.2: DNA Structure ● it was known that DNA was made up of nucleotides joined into long strands by covalent bonds…but HOW were they connected…what was the structure?

  3. DNA Structure ● Made up of nucleotides (monomer) ● Each nucleotide composed of 3 parts: • 5-carbon sugar (DEOXYRIBOSE) • Phosphate group • Nitrogen-containing base ● Adenine (A) ● Thymine (T) ● Guanine (G) ● Cytosine (C)

  4. Chargaff’s Rules What do these data suggest to you?

  5. ● A = T (A pairs with T) ● C = G (C pairs with G)

  6. What DNA Looks Like: ● Rosalind Franklin: used X-ray diffraction patterns to discover that DNA strands twisted around each other like a HELIX

  7. ● Watson & Crick: while trying to build a 3-D model of DNA, Watson saw Franklin’s photograph and measurements and within weeks, he and Crick figured out the structure of DNA

  8. DNA Structure = DOUBLE HELIX (“twisted ladder”) ● Backbone • deoxyribose & phosphate group of each nucleotide ●“Steps of Ladder” • bases (A, G, C, T) ●Any base sequence is possible!

  9. What’s holding the strands together? ●HYDROGEN BONDS!!! ● Hydrogen Bonds form between A and T base pairs as well as between C and G base pairs

  10. 12.3 - DNA Replication Vocabulary: Chromatin Replication DNA polymerase • Key Concept: • What happens during DNA Replication?

  11. The Review ● Prokaryotic cells do not have a nucleus • DNA molecules are located in the cytoplasm • Usually a circular DNA molecule and it is referred to as the cell’s chromosome ● Eukaryotic cells have a nucleus • Can have 1000x more DNA than prokaryotic cells • DNA is located in the form of a number of chromosomes • # of chromosomes varies widely from species to species

  12. DNA molecules are long…how does DNA fit in the nucleus? ● It forms chromosomes! ● DNA coils around proteins called histones and then this chromatin supercoils around itself until chromosomes form

  13. DNA Replication ● before a cell divides, it must copy its DNA so that all cells have a copy of the genetic instructions ● this process involves A LOT of ENZYMES! ● each half of the DNA double helix can serve as a "template" for the replication of another DNA double helix molecule • The strands are said to be complementary

  14. DNA REPLICATION: THE PROCESS 1) An enzyme unwinds & "unzips" DNA (separates the 2 DNA strands) by breaking the hydrogen bonds between base pairs Hydrogen Bonds Breaking!

  15. 2) a complementary base is inserted to each side of the DNA strand with the help of DNA POLYMERASE Why does the “blue” always pair with the “green?”

  16. 3) The sugar-phosphate groups are covalently bonded to the growing DNA chain (new "backbone") 1 nucleotide COVALENT BOND

  17. 4) an enzyme (DNA polymerase) will "proof-read" the order of bases & make corrections

  18. A SIMPLIFIED VERSION…

  19. A Little More Complicated…

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