0801 dna rep
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0801 dna rep



DNA Replication NOt

DNA Replication NOt



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0801 dna rep 0801 dna rep Presentation Transcript

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