4-ppt-Ch12-CellCycle&Division

Cell Cycle Overview

  • Encompasses the series of events in a cell that lead to division and duplication.

  • Transmits chromosomes from one generation to the next.

Objectives of Cell Division

  • Genetically Identical Daughter Cells: Explain how cell division ensures that daughter cells are clones of the parent cell.

  • Reproduction, Growth, and Repair: Discuss the roles of cell division in reproduction (asexual), growth of organisms, and tissue repair.

  • Cell Cycle Parts: Describe the cell cycle phases, particularly interphase (G1, S, G2) and M phase (mitosis and cytokinesis).

  • Mitosis and Cytokinesis Events: Summarize the steps of mitosis (prophase, metaphase, anaphase, telophase) and how cytoplasm divides.

  • Identifying Phases: Be able to recognize stages of the cell cycle through diagrams and micrographs.

  • Spindle Fiber Role: Describe how spindle fibers assist in the segregation of chromosomes during mitosis.

  • Cytokinesis Variations: Differentiate between cleavage furrow in animal cells and cell plate formation in plant cells.

  • Binary Fission: Summarize the steps involved in binary fission, the method of cell division in prokaryotes.

Why Do Cells Divide?

  • Reasons for Division:

    • (a) Reproduction: A means to create new organisms through processes like binary fission or mitosis.

    • (b) Growth and Development: Cells divide to enable growth, allowing organisms to increase in size.

    • (c) Tissue Renewal: Replacement of damaged or dead cells within tissues.

Average Lifespan of Different Cells

  • Various cells in the body have specific lifespans:

    • Head Hair: Grows 0.35 mm/day.

    • Wisdom Tooth Enamel: Stops growing at age 12.

    • Liver Cells: Replaced every 300-500 days.

    • Red Blood Cells: Live about 120 days.

    • Skeletal Muscle Cells: Replaced every 15 years.

    • Pancreatic Beta Cells: Stop growing by age 30.

    • Skin Cells: Renewed every 39 days.

Genome Structure

  • Genome Definition: All genetic information (DNA) present in a cell.

    • Prokaryotes: Have a single, circular chromosome.

    • Eukaryotes: Contain multiple linear chromosomes (e.g., humans: 46 chromosomes).

Chromosome Duplication

  • Prior to division, chromosomes must be duplicated.

    • Structure: Duplicated chromosomes consist of two sister chromatids connected at a centromere.

Chromatin Composition

  • Chromatin: Comprised of DNA and protein.

  • Histones: Proteins that DNA wraps around.

    • Differences:

      • Chromatin: Uncoiled DNA and protein.

      • Chromatids: Joined duplicates of the original chromosome.

Spindle Fibers in Mitosis

  • Microtubule Overlap: Spindle fibers, specifically kinetochores, help in aligning and separating sister chromatids during mitosis.

The Cell Cycle Stages

  • Interphase consists of:

    • G1 Phase: Initial cell growth.

    • S Phase: DNA synthesis/replication.

    • G2 Phase: Preparation for mitosis.

  • M Phase: Includes mitosis and cytokinesis.

Why Cell Division is Necessary

  • Cells must divide for growth, repair, and reproduction.

    • Damaged cells and worn-out cells need replacement and proper functioning.

Phases of Mitosis**

  1. Prophase: Chromatin condenses, and spindle fibers form.

  2. Metaphase: Chromatids align at the metaphase plate.

  3. Anaphase: Sister chromatids separate and move to opposite poles.

  4. Telophase: Chromosomes relax, nuclear membranes reform, cytokinesis occurs.

Cytokinesis Process

  • In animals, it involves the formation of a cleavage furrow through a contractile ring of microfilaments.

  • In plants, a cell plate forms from vesicles that merge in the center and develop into a new cell wall.

Prokaryotic Cell Division

  • Binary Fission: A method of asexual reproduction in prokaryotes, where a single cell divides into two identical daughter cells.

Cell Cycle Timing Summary

  • Total time: 24 hours, broken down into different phases (Gap1, Synthesis, Gap2, M phase).

G0 Phase Definitions

  • G0 Phase: Resting phase where cells are not actively dividing.

    • Cells Entering G0: Typically muscle and nerve cells.

Abnormalities in Cell Division

  • Issues such as skipping the G1 phase or improper DNA copying can lead to malfunctioning cells or multi-nucleated cells.

Microscopic Identification of Cell Phases

  • Identification of mitotic phases via microscopy helps distinguish between plant and animal cells during cell division.