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0801 dna rep

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