Cell Cycle and Mitosis Detailed Notes

Cell Cycle Overview

• Eukaryotic Cell Division

  • Cells move through various phases of the cell cycle during division.

• Phases of the Cell Cycle

  • Interphase
  • Consists of G1 (cell growth), S (DNA synthesis), and G2 (final preparations for mitosis).
  • M Phase (Mitosis)
  • Includes the division of duplicated chromosomes and cytoplasm (cytokinesis).

Observations in Mitosis

• Mitotic Cells

  • Often found in regions like the tips of roots and shoots.
  • Actions observed include cell division, elongation, and differentiation.

• Staining with DNA Stain

  • Helps visualize cells in different phases of the cell cycle.

Detailed Phases of the Cell Cycle

Interphase

• G1 Phase:

  • Cell growth and accumulation of materials for DNA replication.
  • Gathering energy for DNA duplication.
  • Duplicate organelles and assess DNA integrity.

• S Phase:

  • Actual duplication of DNA occurs.
  • Ensure there are no copying errors.

• G2 Phase:

  • Final preparations for mitosis, including additional growth and energy accumulation.

M Phase (Mitosis)

• Division of Duplicated Chromosomes:
  • Mitosis is where the cell divides by separating duplicated chromosomes, followed by cytokinesis.

Cellular Activities in Each Phase

• G1: Cell grows and prepares materials.
• S: DNA replication.
• G2: Checks and prepares for division.
• M: Chromosome alignment and separation.

Mitosis Stages

Prophase

• Chromosomes condense and are visible under a microscope.
• Nuclear envelope still present; cells can look different depending on the stage (early, middle, late).

Prometaphase

• Complete condensation of chromosomes; all are connected to microtubules.
• Nuclear envelope breaks down, making it challenging to distinguish from prophase.

Metaphase

• Chromosomes align at the metaphase plate, defining their position prior to separation.

Anaphase

• Sister chromatids are actively pulled apart towards opposite poles of the cell.

Telophase

• Formation of cleavage furrow in animal cells or cell plate in plant cells.
• Nucleolus reappears; nuclear envelope reforms around chromosomes.

Cell Cycle Checkpoints

• G1 Checkpoint:

  • Ensures sufficient materials and energy to duplicate DNA.

• G2 Checkpoint:

  • Validates that DNA has been duplicated correctly.

• M Checkpoint:

  • Checks alignment of chromosomes before anaphase proceeds.

G0 Phase

• Cell cycle arrest state where cells perform their specialized functions (e.g., liver cells perform liver functions).
• Cells in G0 can re-enter the cell cycle after an injury.

DNA Organization

• Histones:

  • Proteins that assist in DNA packaging by wrapping around DNA to form nucleosomes, allowing for condensation of eukaryotic chromosomes.

• Chromosome States:

  • Chromosomes vary in condensation (more condensed during mitosis, less in interphase).

Cancer and Cell Division

• Differences Between Benign and Malignant Tumors:
  • Benign tumors do not invade nearby tissues or spread, while malignant tumors can metastasize, spreading to other organs through lymphatic or blood systems.
  • Apoptosis (programmed cell death) decreases in malignant cells, promoting uncontrolled growth.