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DNA Structure and Function

DNA Structure and Function. Nucleic Acids. Monomer = nucleotides Structure = three parts: sugar, phosphate, and nitrogen-containing base. Functions. Function #1: Nucleotide monomers can be used as “energy currency” Examples = ATP / ADP. Functions.

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DNA Structure and Function

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  1. DNA Structure and Function

  2. Nucleic Acids Monomer = nucleotides Structure = three parts: sugar, phosphate, and nitrogen-containing base

  3. Functions Function #1: Nucleotide monomers can be used as “energy currency” Examples = ATP / ADP

  4. Functions Function #2: Stores genetic information (traits and inheritance) Examples = DNA, RNA

  5. Nucleotide Structure • Nucleotides – the building blocks of nucleic acids • Made of: • Phosphate • Sugar • Nitrogenous Base

  6. Sugar-Phosphate Backbone Nucleotides connected together with what type of bond? Alternating sugars and phosphates

  7. Nitrogenous Bases • Four bases: • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G)

  8. Base Pairing PURINE with? PYRIMIDINE with? • Bases form hydrogen bonds with each other • A with T • C with G

  9. DNA C G T A Hydrogen bond T A Base pair T A G C G C G C A T C G C G T A A T A T T A T A G C A T Computer model Ribbon model Partial chemical structure Animation: Campbell Ch 10 – DNA Double Helix

  10. 3-D DNA Structure Based on the angle of the bonds (remember what a C with 4 bonds looks like), DNA forms a DOUBLE HELIX

  11. DNA Structure Hydrogen Bonds occur between Nucleotide Bases the bonds between which 2 bases are stronger? thousands of bases, thousands of bonds, thousands of big twists

  12. Polarity Is DNA polar or non-polar?

  13. Determining that DNA is the Genetic Material GRIFFITH: 1928 "Transforming factor”

  14. Determining that DNA is the Genetic Material HERSHEY – CHASE: 1952 Determined that the heredity material was DNA not protein Studied the bacteriophage T2 Head DNA Tail Tail fiber 300,000

  15. Determining that DNA is the Genetic Material Radioactive protein Empty protein shell Radioactivity in liquid Phage Bacterium Phage DNA DNA Batch 1 Radioactive protein Centrifuge Pellet Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. Measure the radioactivity in the pellet and the liquid. Agitate in a blender to separate phages outside the bacteria from the cells and their contents. Radioactive DNA Batch 2 Radioactive DNA Centrifuge Radioactivity in pellet Pellet

  16. Determining the Structure of DNA CHARGOFF: 1949 Different species have different amounts of A, T, C, G A always equals T C always equals G

  17. Determining the Structure of DNA FRANKLIN and WILKINS: 1950’s X-ray crystalographic determination that DNA is a double helix

  18. Determining the Structure of DNA WATSON and CRICK: 1953 Double helix structure of DNA

  19. Determining the Structure of DNA http://www.pbs.org/wgbh/nova/photo51/

  20. DNA Structure in more detail Two strands run in opposite directions

  21. DNA is ANTIPARALLEL • 3’ and 5’ ends • 3’ has OH group • 5’ has phosphate group

  22. Nucleotide Assembly

  23. Organization of DNA • Prokaryotes • Several million base pairs - one circular piece • Related genes grouped together • Mostly coding DNA • Nucleus? 23

  24. Organization of DNA • Eukaryotes • Billions of base pairs – several linear chromosomes • Genes not grouped • Mostly non-coding DNA • Nucleus? 24

  25. DNA in the cell Humans have 3 billion nucleotide base pairs Roughly 6 feet of DNA in the nucleus of each cell How does it all fit?

  26. DNA is tightly packaged into chromosomes

  27. CHROMATIN - eukaryotes ONLY • Histone proteins: the spools around which DNA winds • 9 Histone proteins + DNA = Nucleosome • core of 8 histone proteins • DNA wrapped around • 1 “H1” histone

  28. Higher Chromatin Organization

  29. And even higher chromatin organization!

  30. And the highest organization!Meet the chromosome

  31. Chromosome Animation http://www.biostudio.com/demo_freeman_dna_coiling.htm

  32. Gene Expression Every cell in your body came from 1 original egg and sperm Every cell has the same DNA and the same genes 32

  33. Gene Expression • Every cell in your body came from 1 original egg and sperm • Every cell has the same DNA and the same genes • Each cell is different, specialized • Differences due to gene expression • Which genes are turned on • When the genes are turned on • How much product they make 33

  34. Gene Expression DNA must be copied when cells divide so that DNA is the same in all cells

  35. DNA Replication T A T A T T T A A A C G C G C G C G G C G C G C G C G C C A T A T T T A A A A T A T T T A A Nucleotides Parental molecule of DNA Both parental strands serve as templates Two identical daughter molecules of DNA • The Watson-Crick model of DNA structure suggested a mechanism for its replication • DNA strands separate • Enzymes use each strand as a template to assemble new nucleotides into complementary strands

  36. DNA Replication Animation: Campbell Ch 10 – 10_04 DNA Replication Overview Animation: Starr Ch 13 – Replicating DNA Detail http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/dna_replication.htm

  37. DNA Replication Summary Helicase breaks hydrogen bonds to separate strands DNA Polymerase pairs new bases and creates two new strands Semi-conservative Leading strand = continuous Lagging strand = segments connected by ligase

  38. DNA Replication in Eukaryotes • Eukaryotic DNA is very long and linear • replication begins at many points

  39. DNA Replication in Prokaryotes prokaryotic DNA is circular replication begins at one point

  40. Repair of Mistakes Error rate during replication: 1 in 100,000 nucleotides = about 3,000 mistakes per replication (human) Error rate in completed daughter DNA molecules: 1 in 10,000,000,000 nucleotides

  41. Repair of Mistakes • Enzymes proofread DNA sequences during DNA replication and repair damaged DNA • Mismatch repair enzymes replace incorrectly paired nucleotides • Nucleotide excision repair enzymes chop out incorrect or damaged bases

  42. Repair of Mistakes When proofreading and repair mechanisms fail, an error becomes a mutation – a permanent change in the DNA sequence

  43. When would the cell replicate DNA? Any time it is going to divide so that new cells have enough DNA

  44. DNA Structure Review Covalent bonds on sides connecting nucleotides Hydrogen bonds between bases A pairs with T C pairs with G 5’ end = phosphate 3’ end = OH on sugar

  45. Cell Division

  46. Cell Division Questions to consider… Where? Why? How?

  47. Cell Division Mitosis in everything else Meiosis in sexual reproduction. • Eukaryotic cells utilize two types of cell division: • mitosis • meiosis

  48. Why Divide? To replace dead or dying cell To produce more cells to enlarge the organism Reproduction

  49. Binary Fission asexual reproduction used by most prokaryotes and protists Results in the reproduction of a livingcellby division into two equal or near-equal parts.

  50. BINARY FISSION

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