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Questions and Answers
What are the key stages of mitosis and meiosis?
Prophase, Metaphase, Anaphase, Telophase
What happens during cytokinesis?
Mitosis ensures each daughter cell receives a haploid complement of chromosomes.
False
What is interphase?
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The cell cycle is described in the sequence: G1 → S → G2 → _____
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What are cyclins?
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Which checkpoint is considered the most important?
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The p53 protein acts as a tumor suppressor.
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What can lead to cancer in relation to the cell cycle?
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How long does mitosis typically take?
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Study Notes
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.
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