Study Notes for Chapter on the Cell Cycle

Biological Science - Chapter 12 Overview

  • Chapter Title: The Cell Cycle

  • Chapter Objectives:

    • Understand the life cycle of a cell culminating in division.

    • Key questions include: "How does cell division take place?"

  • Focus Areas:

    • The four phases of the cell cycle: Mitosis, Cytokinesis, and Cancer (as concerned with uncontrolled division).

Learning Objectives for Chapter 12

  • Key Learning Outcomes:

    • Explain the phases of the cell cycle.

    • Explain the key steps of mitotic cell division.

    • Explain the fate of chromosomes throughout the cell cycle.

    • Understand factors that regulate the cell cycle.

    • Explain the importance of cell cycle control in the context of cancer.

Chromosome Structure and Function

  • Chromosome Definition:

    • A chromosome is defined as a single, long molecule of double-stranded DNA wrapped around proteins known as histones.

  • Gene Definition:

    • A gene is defined as a section of DNA forming a functional unit, with chromosomes containing hundreds to thousands of genes.

  • Discussion Plan:

    • Information on how gene information is utilized will be covered in Chapter 14 and onward.

Overview of the Mitotic Cell Cycle

  • Phases of the Mitotic Cell Cycle:

    1. S (Synthesis) Phase: Copying of the DNA.

    2. M (Mitotic) Phase: Separating the DNA copies.

    3. Cytokinesis: Division of the cytoplasm to form two complete cells.

Structure of Skin and Cell Cycling

  • Epidermis Composition:

    • Consists of various layers and cells:

    • Stratum Corneum: Comprises dead keratinocytes.

    • Stratum Lucidum, Granulosum, Spinosum, and Basale: Include living keratinocytes and stem cells.

  • Role of Cells:

    • Dividing keratinocyte stem cells are located in the Stratum Basale.

M Phase Processes

  • M Phase Components:

    • Mitosis involves five sub-phases:

    1. Prophase: Chromatin condenses.

    2. Prometaphase

    3. Metaphase

    4. Anaphase: Sister chromatids separate into daughter chromosomes.

    5. Telophase: Nuclear envelope re-forms.

    • Cytokinesis: Cytoplasm and new nuclei are separated into two new cells.

Cytokinesis Process

  • Completion of Mitosis: Defined as having two independent nuclei formed, immediately followed by cytokinesis.

  • Mechanism: Plasma membrane begins to pinch in, leading to the division of cytoplasm and nuclei.

  • Outcome: Completion results in the formation of two daughter cells.

Cell Cycle Dynamics

  • Graphical Representation:

    • Y-axis indicates "Amount of DNA" not the number of chromosomes.

    • Cycles of G1, S, G2, and M phases.

Chromosome Movement During Anaphase

  • Mechanics of Movement:

    • Kinetochore microtubules remain stationary while shortening due to the loss of tubulin subunits from their plus ends.

    • Movement is facilitated by motor proteins and the fraying of microtubules and involves kinetochores.

Controls of the Cell Cycle

  • Variations in Cell Cycle Length:

    • Vary significantly among different cell types primarily due to the variability of the G1 phase.

    • Non-dividing cells can remain in G1 phase, entering an arrested state known as G0.

  • Cell Cycle Checkpoints:

    • Utilize positive (e.g., sufficient size, nutrients, growth factors) and negative signals (e.g., DNA damage) to regulate the progression through the cycle.

Quality Control - G2 Checkpoint

  • Cells proceed to the M phase if:

    • Mitosis Promoting Factor (MPF) has accumulated.

    • Inhibitory phosphate on Cdk removed, which is contingent upon:

    • Completion of chromosome replication and undamaged DNA.