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DNA Structure & Function

DNA Structure & Function. Biology 12. Functions of DNA. Controls cellular functions Central Dogma – DNA makes … DNA (replication) RNA (transcription) Protein (translation). DNA. DNA. Central Dogma of molecular biology!. RNA. RNA. Protein. Protein. Structure of DNA.

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DNA Structure & Function

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  1. DNA Structure& Function Biology 12

  2. Functions of DNA • Controls cellular functions • Central Dogma – DNA makes … • DNA (replication) • RNA (transcription) • Protein (translation)

  3. DNA DNA Central Dogma of molecular biology! RNA RNA Protein Protein

  4. Structure of DNA • Made of nucleotides • Double helix • Two parallel strands wound around each other • Like a twisted ladder

  5. What is a Nucleotide? • Each is made up of: • 1 deoxyribose sugar (a 5 carbon sugar) • 1 phosphate group • 1 of 4 nitrogenous bases

  6. Like a Twisted Ladder … • Sides: • Made of alternating sugars & phosphates • “Sugar phosphate backbone” • Rungs: • Made of base pairs

  7. DNA Runs Antiparallel Parallel but in opposite directions 5’ end of one strand of DNA aligns with 3’ end of the other strand

  8. What is a 5` & 3` end? • Carbons of a deoxyribose sugar are numbered 1 to 5 #1 - attaches to nitrogenous base #3 - attaches to phosphate group ENTERING deoxyribose sugar #5 - attaches to phosphate group EXITING deoxyribose sugar

  9. Complimentary Base Pairing • Pairing of nitrogenous base on one strand with the corresponding nitrogenous base • adenine (A) always pairs with thymine (T) • guanine (G) always pairs with cytosine (C)

  10. Hydrogen Bonds • Base pairs held together by weak hydrogen bonds • 2 between A&T • 3 between G&C • Why do they need to be weak?

  11. Pyrimidine Single ring Thymine (T) & Cytosine (C) Purine Double ring Adenine (A) & Guanine (G) Pyrimidine vs. Purine (#5 pg216)

  12. Goldilocks Rule! Why do you think the bases match up this way? Purine + Purine = toobig Pyrimidine + Pyrimidine = toosmall Purine + Pyrimidine = just right!

  13. #2 – Page 216 • Purine & Pyrimidine always bond • Why can’t A-C and G-T form pairs? • Incorrect number of hydrogen bonds required

  14. Rule of Chargaff • Amount of A = T • Amount of G = C • Why was this important to the discovery of DNA?

  15. #6 – Page 216 • 20% = Thymine • Determine % of other bases • 20% = A • 60% remains, so: • 30% = G • 30% = C

  16. How to Read a DNA Strand • Start at the 5` end • CGAT • Start at 3’ end for complimentary strand (opposite strand) • GCTA

  17. #3 – Page 216 • DNA template: • 5’ ATGCCTTA 3’ • Determine complementary strand: • 3’ TACGGAAT 5’

  18. Short Video DNA Structure

  19. 5’ thymine guanine 3’ 5’ end adenine 3’ cytosine 3’ 5’

  20. Reading the DNA 3’ 5’ end DNA Template: 5’ C A G T 3’ Complimentary Strand: 3’ G T C A 5’ 3’ 5’

  21. Any Questions so far?

  22. Draw a DNA Molecule • Create the sequence: • TAC CAG GGC ATC • Show: • Directionality (3’ and 5’ ends) • Hydrogen bonds • Create a legend

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