30 Study Notes on Cell Division and Mitosis

Introduction to Cell Division

  • Overview of lecture and primary focus:

    • Discuss cell division with an emphasis on cytoskeleton changes and the cell cycle.

    • Learning outcomes:

    • Clearly describe mitosis and outline the different phases of cell division.

    • Understand cytoskeletal and nuclear envelope changes during cell division.

    • Summary slides available for revision.

Visualizing Mitosis and Cytoskeletal Changes

  • Visual aids:

    • Video depicting metaphase (one phase of mitosis):

    • DNA/chromatin/sister chromatids are marked in blue.

    • Kinetochore highlighted in pink, central to sister chromatids.

    • Microtubules (tubulin) painted green.

  • Cytoskeletal changes during cell division:

    • Focus on microtubules due to their significant role:

    • Interaction with motor proteins: kinesin and dynein.

    • Notable exception: kinesin moving to the minus end instead of the plus end.

    • Intermediate filaments:

    • Emphasis on the nuclear lamina as part of the nuclear envelope.

    • Actin filament: forms a contractile ring in cytokinesis.

Key Proteins Involved in Cell Cycle

  • Important proteins discussed in this lecture:

    • MCDK (M-phase Cyclin-dependent Kinase):

    • Recall from earlier cell cycle lectures.

    • Proteins facilitating mitosis:

    • Condensin: aids in DNA condensation.

    • Kinetochore: assists in sister chromatid movement.

    • APCC (Anaphase-promoting Complex): crucial for cell cycle regulation.

    • Cohesin, securin, separase: proteins governing sister chromatid integrity and separation.

Dynamic Nature of Cell Division

  • Emphasis on dynamic processes during the cell cycle:

    • Continuous progression through various phases:

    • From one cell to two, four, eight, and so forth.

    • Key phase: M phase covers mitosis and cytokinesis.

Cell Cycle Overview

  • Distinction between interphase and M phase:

    • Interphase:

    • Preceding M phase, characterized by low DNA condensation.

    • G2 phase:

    • Preparation for mitosis:

      • Includes duplicated DNA and centrosomes.

      • Intact nuclear envelope for genetic protection.

  • Phases of Mitosis:

    • Prophase:

    • Centrosome separation, mitotic spindle formation.

    • DNA condenses into sister chromatids, kinetochore formation begins.

    • Prometaphase:

    • Breakdown of the nuclear envelope:

      • Microtubules invade, binding to kinetochores.

    • MCDK levels remain elevated, essential for spindle assembly.

    • Metaphase:

    • Alignment of sister chromatids at the spindle equator:

      • Perfect connection and alignment crucial for subsequent steps.

    • Anaphase:

    • Separation of sister chromatids:

      • Driven by shortening of kinetochore microtubules and movement of centrosomes.

    • APCC activation leading to degradation of securin.

      • Allows separase activation, degrading cohesin.

    • Telophase:

    • Reformation of the nuclear envelope:

      • Dephosphorylation of lamins.

      • Formation of the contractile ring begins with actin involvement.

Cytokinesis: The Final Step of Division

  • Cytokinesis defined:

    • Actual division of the cell;

    • The contractile ring created by actin and myosin pinches the cell into two.

  • Importance of protein regulation:

    • RhoA activation leading to actin and myosin enhancement in contractile ring formation:

    • Activation of formin for actin polymerization.

    • RhoA also activates myosin II, facilitating contraction.

Summary of Mitosis and Cytokinesis Phases

  • Full cycle overview:

    • Start in interphase (G2) with:

    • Duplicated DNA, intact nuclear envelope, duplicated centrosomes.

    • Progression through prophase to cytokinesis, with significant protein involvement and regulation at each phase:

    1. Prophase: intact nuclear envelope, condensed DNA.

    2. Prometaphase: fragmentation of nuclear envelope, microtubules connect to kinetochores.

    3. Metaphase: perfect attachment of kinetochore microtubules.

    4. Anaphase: separation of sister chromatids.

    5. Telophase: protection of separated sister chromatids, beginning of contractile ring.

    6. Cytokinesis: division into two daughter cells with intact nuclear envelopes.

Questions and Conclusion

  • Discussion on decondensation of DNA:

    • Occurs in interphase G1 phase, not before completing proper separation.

  • Final remarks and encouragement for revision through provided materials and videos.

  • Wishes for a good weekend with encouragement for engagement with the material in upcoming classes.