BIO 4.3

  • Cell Cycle - all activities that a cell goes through in its life

    • Growth, DNA replication, cellular division (mitosis)

  • Cells need to divide for an organism to grow and replace old cells

  • Interphase - longest phase - prepares cell for division, $G_1/G_0$, S phase, $G_2$

  • Mitosis - cellular division of somatic calls - not sex calls

  • Spends 90% of tre in interphase: working & growing, breaking down sugars, synthesizing macromolecules

    • Preparatory phase for mitosis

    • Visible in cell during phase: nucleus and nuclear membrane, chromosomes in form of threadlike chromatin

    • $G_1$ → growth & normal operation of call

    • $G_0$ → cell not dividing

    • S phase → DNA replication

    • $G_2$ → cell prepares for mitosis

  • DNA replication copies the genetic information of a cell

    • Each cell needs complete set of DNA

    • Before cell can divide, needs to replicate DNA

    • Happens during interphase → S phase → between G1 & G2

  1. DNA molecule with 2 strands begins to unwind in preparation for replication

  2. Helicase - unzips 2 strands of DNA -> replication fork

  3. DNA polymerase - adds free nucleotides to part with original strands

    1. Leading strand - replicated continuously in same direction as moving fork

      1. 3’ to 5’ DNA replicated synthesizing DNA continuously in 5’ to 3’ direction

    2. Lagging strand - replicated in opposite direction in form of short Okazaki fragments

      1. Okazaki fragments added from 5’ end in 5’ to 3’ segments

  4. DNA Ligase - zip new and old strand together

    1. 2 new DNA molecules formed -> each with 1 new and 1 old

  5. DNA polymerase proofreads nucleotides and corrects them

    1. Many forms of DNA damage can lead to cancer

    2. Cells have processes to correct most of these mistakes prior to mitosis

  • Replication semi-conservative - 1 old and 1 new strand