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.