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0801 dna rep

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DNA Replication NOt

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0801 dna rep

  1. 1.
  2. 2. Cell Division Cycle <ul><li>New cells are produced by division of existing cells </li></ul><ul><li>If many new cells are needed, cells go through a cycle of events again and again </li></ul><ul><li>This is called the cell division cycle </li></ul>
  3. 3. <ul><li>The longest phase in this cycle is interphase </li></ul><ul><li>During interphase the cell carries out many biochemical reactions and grows larger , increase numbers of organelles </li></ul><ul><li>The DNA molecules in the chromosomes are not coiled up (chromatin) and the genes on them can be transcribed to allow protein synthesis </li></ul><ul><li>If the cell is going to divide again, the DNA is all replicated </li></ul><ul><li>These and other processes make interphase a very active period for a cell </li></ul>DNA replication chromosomes condense cell grows and develops
  4. 4. Interphase: DNA Replication <ul><li>DNA replication is a way of copying DNA to produce new molecules with the same base sequence </li></ul>
  5. 5. antiparallel strands of DNA
  6. 6. Base Pairing during Replication <ul><li>Each old strand serves as the template for complementary new strand </li></ul>
  7. 7. <ul><li>Semiconservative model of DNA replication </li></ul><ul><ul><li>Each molecule formed by replication consists of one new strand and one old strand conserved from the parent DNA molecule thus each new DNA molecule is a combination of one parent strand and one newly replicated strand </li></ul></ul>
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  10. 10. Replication begins at multiple sites at the same time E. Coli
  11. 11. Continuous and Discontinuous Assembly <ul><li>Strands can only be assembled continuously toward the replication fork in the 5’ to 3’ direction </li></ul><ul><li>The discontinuous side must be assembled in chunks called Okazaki fragments </li></ul>
  12. 12.
  13. 13. 1. 2. 3. 4. 5. 6. Summary of DNA replication:
  14. 14. <ul><li>Step 1. Helicase enzyme unwinds the parent double helix. Hydrogen bonds are broken and strands are separated </li></ul><ul><li>Step 2. Binding proteins stabilize unwound DNA </li></ul><ul><li>Step 3. Single strands act as templates for new strands. Free nucleotides are present in large numbers around the replication fork. DNA polymerase synthesizes the continuous 5’  3’ leading strand by forming hydrogen bonds between the complementary bases </li></ul><ul><li>Steps 4. and 5. Primase enzyme and another DNA polymerase enzyme synthesize the lagging strand fragments (Okazaki fragments) </li></ul><ul><li>Step 6. DNA ligase joins the Okazaki fragments together. The daughter DNA molecules each rewind into a double helix </li></ul>DNA Replication Summary
  15. 15. Enzyme Roles and Names
  16. 16. Where does the energy come from for DNA Replication? <ul><li>Deoxynucleoside triphosphates (dNTP) </li></ul><ul><li>Base + deoxyribose + THREE phosphates </li></ul><ul><ul><li>The 2 extra phosphates are lost and this provides the energy to bond one nucleotide to another </li></ul></ul>
  17. 17. histone protein DNA strand DNA wrapped around histones DNA-histone complex folded folding again folding yet again chromosome : very densely packed DNA and proteins structure of chromosome DNA + proteins
  18. 18. DNA gene = a discrete unit of hereditary information (DNA) locus = location of a gene on a chromosome
  19. 19.
  20. 20. <ul><li>At the end of interphase when DNA replication has been completed, the cell begins mitosis </li></ul><ul><li>In mitosis the nucleus divides to form two genetically identical nuclei </li></ul><ul><li>Towards the end of mitosis, cytoplasm of the cell starts to divide, eventually two cells are formed, each containing one nucleus </li></ul><ul><li>The process of dividing the cytoplasm to form two cells is cytokinesis </li></ul><ul><li>The two cells begin interphase when mitosis & cytokinesis have been completed </li></ul>DNA replication chromosomes condense cell grows and develops

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