Cell Growth & Division

Cell Growth

  • Limiting cell size
    • Why an ant can't be the size of a human: genetics, diffusion distance.

Limitations of Cells

  • Stress of normal functions hurts the cell if it becomes too large.

  • Too much to do for the DNA.

    • The DNA controls the cell.
    • If the cell gets too large, the DNA will be under too much stress to function properly.

  • Exchanging Materials

    • Diffusion and osmosis are controlled by the volume of the cell.
    • If the cell gets too large, the nutrients will not be able to reach the inside/middle of the cell.
    • Exocytosis of wastes will slow with a larger volume.

  • Surface Area-to-Volume Ratio

    • As the surface area of a cell increases, the volume increases faster.

    • Surface Area: Length x width x # of sides.

    • Volume: Length x width x Height.

    • Creates a ratio of surface area to volume.

    • Example:

      • 1 cm cell: Surface Area = 1 \text{ cm} \times 1 \text{ cm} \times 6 = 6 \text{ cm}^2, Volume = 1 \text{ cm} \times 1 \text{ cm} \times 1 \text{ cm} = 1 \text{ cm}^3, Ratio = 6/1 = 6:1
      • 2 cm cell: Surface Area = 2 \text{ cm} \times 2 \text{ cm} \times 6 = 24 \text{ cm}^2, Volume = 2 \text{ cm} \times 2 \text{ cm} \times 2 \text{ cm} = 8 \text{ cm}^3, Ratio = 24/8 = 3:1
      • 3 cm cell: Surface Area = 3 \text{ cm} \times 3 \text{ cm} \times 6 = 54 \text{ cm}^2, Volume = 3 \text{ cm} \times 3 \text{ cm} \times 3 \text{ cm} = 27 \text{ cm}^3, Ratio = 54/27 = 2:1

Division of the Cell

  • Before getting too large, the cell undergoes cell division.
    • Makes two daughter cells.
  • Cell division will solve the cell's problems.
    • DNA is copied and separated into the daughter cells.
    • It reduces overall cell volume.

Cell Division

  • Chromosomes

    • Are made of DNA.
    • Each species has a specific number of chromosomes.
    • Each chromosome is copied before cell division.
      • Chromosomes are made of sister chromatids.
      • Sister chromatids are held together by the centromere.
      • Each new cell receives one chromatid.

  • Cell Reproduction

    • Commonly called Cell Cycle.
      • Cycle of Growth and Reproduction.
    • Made of various phases.
    • 2 main areas:
      • Interphase: Cell Growth
        • 3 stages: G1-phase, S-phase, G2-phase
      • Mitosis: Nuclear Division
        • Prophase: 1st phase
          • Nuclear Envelope dissolves.
          • Chromatin condenses into chromatids.
          • Centrioles migrate to the poles and form spindle.

  • Anaphase:

    • Chromatids separate and are moved to opposite sides of cell

  • Telophase:

    • Prophase in reverse
    • Envelope returns (Nucleus Reforms)
    • Spindle leaves
    • Chromatids decondense into Chromatin

  • Cytokinesis: Cyto: cell, Kinesis: Movement

    • Division of cell
    • All organelles have been duplicated and separated
    • Cell membrane (wall) pinches (cuts) the cell in half

Control of Cell Cycle

  • Normal Control
    • Cells send signals (cyclin protein).
      • This will tell the cells when they need to reproduce.
      • Cells will reproduce until they reach their boundaries.
  • Cancer: Uncontrolled Cell Growth
    • Cancer cells don't respond to normal regulatory signals.
    • Cell cycle is disrupted.
    • Cells grow and divide uncontrollably. Cell cycle is disrupted.