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DNA Structure PowerPoint


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DNA Structure PowerPoint

  1. 1. IB Topics 3 and 7
  2. 2. #1. DNA Structure (an overview) <ul><li>DNA has three main components </li></ul><ul><ul><li>1. deoxyribose (a pentose sugar) </li></ul></ul><ul><ul><li>2. base (there are four different ones) </li></ul></ul><ul><ul><li>3. phosphate </li></ul></ul>
  3. 3. #2. The Bases <ul><li>They are divided into two groups </li></ul><ul><ul><li>Pyrimidines and purines </li></ul></ul><ul><li>Pyrimidines (made of one 6 member ring) </li></ul><ul><ul><li>Thymine </li></ul></ul><ul><ul><li>Cytosine </li></ul></ul><ul><li>Purines (made of a 6 member ring, fused to a 5 member ring) </li></ul><ul><ul><li>Adenine </li></ul></ul><ul><ul><li>Guanine </li></ul></ul><ul><li>The rings are not only made of carbon (specific formulas and structures are not required for IB) </li></ul>
  4. 4. #3. Nucleotide Structure <ul><li>Nucleotides are formed by the condensation of a pentose sugar, phosphate and one of the 4 bases </li></ul><ul><li>The following illustration represents one nucleotide </li></ul>
  5. 5. <ul><li>Nucleotides are linked together by covalent bonds called phosphodiester linkage </li></ul>#3. Nucleotide Structure
  6. 6. #4. DNA Double Helix and Hydrogen Bonding <ul><li>Made of two strands of nucleotides that are joined together by hydrogen bonding </li></ul><ul><li>Hydrogen bonding occurs as a result of complimentary base pairing </li></ul><ul><ul><li>Adenine and thymine pair up </li></ul></ul><ul><ul><li>Cytosine and guanine pair up </li></ul></ul><ul><ul><li>Each pair is connected through hydrogen bonding </li></ul></ul><ul><ul><li>Hydrogen bonding always occurs between one pyrimidine and one purine </li></ul></ul>
  7. 7. <ul><li>Complimentary base pairing of pyrimidines and purines </li></ul>#4. DNA Double Helix and Hydrogen Bonding
  8. 8. #4. DNA Double Helix and Hydrogen Bonding
  9. 9. <ul><li>Adenine always pairs with thymine because they form two H bonds with each other </li></ul><ul><li>Cytosine always pairs with guanine because they form three hydrogen bonds with each other </li></ul>#4. DNA Double Helix and Hydrogen Bonding
  10. 10. <ul><li>The ‘backbones’ of DNA molecules are made of alternating sugar and phosphates </li></ul><ul><li>The ‘rungs on the ladder’ are made of bases that are hydrogen bonded to each other </li></ul>#5. DNA Double Helix
  11. 11. #6. Antiparallel strands The strands run opposite of each other. The 5’ end always has the phosphate attached. 5’ 3’ 3’ 5’
  12. 12. Assignment (in your notebook) <ul><li>1. Draw the structure of ribose and number the carbons </li></ul><ul><li>2. Draw a schematic representation of a nucleotide. Label the sugar, base and phosphate. </li></ul><ul><li>3. What are the complimentary base pairs to a DNA strand that has the following order A T A C C T G A A T? </li></ul><ul><li>4. Draw a schematic representation of an unwound DNA double helix using the base pairs from your answer in question 3. </li></ul><ul><ul><li>Include the number of hydrogen bonds between each base pair. Be sure to label all of the bases and the 5’ and 3’ ends of the structure. </li></ul></ul>
  13. 14. #6. When phosphodiester links are formed . . . <ul><li>A. When the covalent bonds are formed between nucleotides the attach in the direction of 5’ ->3 ’ </li></ul><ul><li>B. The 5’ end of one nucleotide attaches to the 3’ end of the previous nucleotide </li></ul>
  14. 15. #7. Nucleosome structure <ul><li>Nucleosome are the basic unit of chromatin organization </li></ul><ul><li>In eukaryotes DNA is associated with proteins </li></ul><ul><ul><li>(in prokaryotes the DNA is naked) </li></ul></ul><ul><li>Nucleosomes = basic beadlike unit of DNA packing </li></ul><ul><ul><li>Made of a segment of DNA wound around a protein core that is composed of 2 copies of each of 4 types of histones </li></ul></ul>
  15. 16. <ul><li>Nucleosomes have: </li></ul><ul><ul><li>8 histones in the core </li></ul></ul><ul><ul><li>DNA wrapped twice around the core </li></ul></ul><ul><ul><li>One histone holding the nucleosome together </li></ul></ul><ul><ul><li>A DNA ‘linker’ continuing towards the next nucleosome </li></ul></ul>#7. Nucleosome structure
  16. 17. <ul><li>The DNA has a negatively charged backbone (because of the phosphate groups) </li></ul><ul><li>The proteins (the histones) are positively charged </li></ul><ul><li>The DNA and proteins are electromagnetically attracted to each other to form chromatin </li></ul>#7. Nucleosome structure
  17. 18. #8. Genes <ul><li>Genes=units of genetic information (hereditary information) </li></ul><ul><li>Order of nucleotides make up the genetic code </li></ul><ul><li>Genes can contain the information for one polypeptide </li></ul><ul><li>Genes can also regulate how other genes are expressed </li></ul><ul><li>All cells of an organism contain the same genetic information but they do not all express the same genes </li></ul><ul><ul><li>THIS IS CELL DIFFERENTIATION </li></ul></ul><ul><ul><li>Cells differentiate by genes that are activated </li></ul></ul>
  18. 19. <ul><li>Repetitive sequences-part of the non-coding section of DNA </li></ul><ul><ul><li>Function-unknown </li></ul></ul><ul><ul><li>Can be used in DNA profiling (DNA fingerprinting) </li></ul></ul>#8. Genes