phases of mitosis

Overview: The discussion focuses on the phases of cell division (mitosis) and the processes involved in eukaryotic cells.
Purpose: Understand the key differences and mechanisms during different phases of mitosis, including prophase, prometaphase, metaphase, anaphase, telephase, and cytokinesis.

Reminder for Students:
- Circle 12 PM as it aligns with the class schedule.
- Leave completed sheets on the designated table for attendance tracking.

Definition: Prophase is the first stage of mitosis where chromatin condenses into visible chromosomes.
Changes during Prophase:
- The nucleolus disappears.
- The spindle apparatus begins to form from microtubules.
- Different types of microtubules are assembled.
Types of Microtubules:
- Aster microtubules: Supporting the centrosome and centrioles.
- Polar microtubules: Push the two poles apart.
- Kinetochore microtubules: Not yet functional in this phase, they're just being synthesized.
Key Differences from Prometaphase:
- Kinetochore microtubules in prophase are in the process of assembly, while in prometaphase they attach to the kinetochore around the centromere.

Definition: The second stage of mitosis where the nuclear membrane is completely disassembled.
Changes:
- The nuclear envelope disappears and is converted into vesicles.
- Kinetochore microtubules attach to the kinetochore surrounding the centromere, making them functional.
- Each pair of sister chromatids is connected to both poles, a critical feature differentiating mitosis from meiosis.

Definition: The stage of mitosis where chromosomes align at the cell's equator (metaphase plate).
Key Features:
- Arrangements of sister chromatids occur randomly, without a specific order (e.g., an X chromosome next to a paternal chromosome).
- Each pair of sister chromatids is connected to both poles, ensuring equal distribution during separation.

Definition: The pivotal stage of mitosis responsible for maintaining the chromosome number.
Changes:
- Polar microtubules elongate (polymerize) to push the centrosomes further apart.
- Kinetochore microtubules shorten (depolymerize) pulling sister chromatids apart into individual chromosomes.
Importance:
- Ensures that chromosome number remains constant by creating individual chromosomes from sister chromatids.
- Cohesin proteins are digested to facilitate separation of chromatids.
Example Numbers:
- Start with 2n = 20 in the G1 phase.
- S phase doubles chromosomes to 40 (as sister chromatids).
- Anaphase results in quantifiable separation: 20 chromosomes on each side (20 + 20).

Definition: The final phase of mitosis characterized by the decompacting of chromosomes.
Changes:
- Chromosomes become thread-like and extend.
- Nucleolus reappears, indicating RNA synthesis resumes.
- Nuclear envelope reforms around each set of chromosomes.
- Spindle apparatus disassembles, marking the end of nuclear division (mitosis).

Definition: The division of the cytoplasm following mitosis, resulting in two daughter cells.
Mechanism in Animal Cells:
- Actin filaments polymerize beneath the plasma membrane, forming a cleavage furrow that pinches the cell apart.
- Myosin motor proteins help in the contraction and pinching off of cells.
Mechanism in Plant Cells:
- Vesicles from the Golgi complex transport carbohydrates to the middle of the cell to assemble a cell plate.
- The cell plate extends until it fuses with the plasma membrane.
- Formation of the middle lamella and the primary cell wall, composed primarily of pectin and cellulose, follows.
Key Points:
- Cytokinesis differs between animal (cleavage furrow) and plant cells (cell plate).

Overview of the importance of each mitotic phase in cell division and the maintenance of chromosome number.
Discussion of how understanding these processes can inform studies in genetics, cancer research, and developmental biology.
Real-world applications include targeted cancer therapies that disrupt the cell cycle.