Untitled Quiz

Mitosis and Meiosis Overview

• Mitosis is nuclear division, ensuring each daughter cell has a diploid complement of chromosomes identical to the parent cell.
• Cytokinesis follows mitosis, dividing the cytoplasm into two daughter cells.

Key Stages of Mitosis

• Chromosome Duplication: Occurs before nuclear division; DNA replication leads to chromosome duplication.
• Chromosome Separation: Each chromosome divides longitudinally into two identical halves, moving to opposite poles before reaching daughter nuclei.
• Interphase: Non-mitotic cells are in this stage; chromosomes aren’t visible, consisting of G1, S (DNA synthesis), and G2 phases.

Cell Cycle

• The cell cycle includes G1 → S → G2 → M phases; G1 and G2 are intermission phases without DNA replication.
• Cyclins regulate the cell cycle and activate cyclin-dependent kinases; they degrade after fulfilling their function.
• Important checkpoints exist at G1/S and G2/M transitions to ensure proper cell growth and DNA integrity.

Regulation of Cell Cycle

• Checkpoints are crucial for preventing uncontrolled cell division; transition from G1 to S requires adequate cell size and timing since the previous mitosis.
• G2/M checkpoint confirms completion of DNA replication and repair.
• Abnormalities, such as defective p53 (a tumor suppressor), contribute to cancer, allowing rapid cell division.

Role of p53 Gene

• TP53 gene codes for p53 protein, which prevents uncontrolled cell growth.
• p53 acts as a guardian of the genome, inhibiting the cell cycle when abnormalities are detected.

Spindle Assembly Checkpoint (SAC)

• The most critical checkpoint occurs in metaphase, ensuring proper alignment of chromosomes before proceeding with mitosis.

Duration of Cell Cycle

• Cell cycle duration varies by cell type, typically taking 18 to 24 hours; mitosis is relatively short, lasting 0.5 to 2 hours.

Stages of Mitosis Detailed

• Prophase: Chromosomes condense and become visible; the nuclear envelope breaks down, and nucleoli disappear.
• Metaphase: Chromosomes align at the equatorial plane of the cell, preparing for separation.