M Phase of the Cell Cycle

Summary

This lesson covers the M phase of the cell cycle, focusing on mitosis and cytokinesis. It reviews the cell cycle phases: G1, S, G2 (interphase), and M (cell division). Mitosis is divided into four stages: prophase (chromosomes form, nuclear membrane disappears), metaphase (chromosomes align at the cell equator), anaphase (sister chromatids separate and move to poles), and telophase (nuclear membranes reform). Cytokinesis follows, dividing the cytoplasm to form two identical daughter cells. In animal cells, this occurs by pinching the cell membrane; in plant cells, a cell plate forms. The M phase results in two identical daughter cells.

Takeaways

• 🔬 The M phase of the cell cycle includes mitosis and cytokinesis, representing cell division.
• 📅 The G1, S, and G2 phases make up interphase, while the M phase follows as the final phase.
• 🔄 Mitosis, the division of the nucleus, is broken down into four phases: prophase, metaphase, anaphase, and telophase.
• 🧬 During prophase, chromatin condenses into chromosomes, and the nucleolus and nuclear membrane disappear.
• 📏 In metaphase, spindle fibers align the chromosomes along the cell's equator, creating an end-to-end alignment.
• 🔗 Anaphase involves spindle fibers separating sister chromatids at their centromeres, pulling them to opposite poles.
• 🎯 Telophase sees the reformation of the nuclear membrane around each set of chromosomes and the nucleolus becoming visible again.
• 🧩 Cytokinesis, the division of the cytoplasm, completes the M phase, resulting in two identical daughter cells.
• 🌱 In animal cells, cytokinesis occurs through the inward pinching of the cell membrane, while in plant cells, a cell plate forms due to the rigid cell wall.
• 📚 Key points: The M phase ends with two daughter cells identical to each other and the original cell, comprising mitosis (nucleus division) and cytokinesis (cytoplasm division).

Q & A

What are the phases of the cell cycle mentioned in the script?

The phases of the cell cycle mentioned are G1, S, G2 (collectively known as interphase), and the M phase (mitosis and cytokinesis).

What occurs during the M phase of the cell cycle?

During the M phase, cell division occurs through two processes: mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

What happens during prophase in mitosis?

During prophase, chromatin condenses into chromosomes, the nucleolus disappears, spindle fibers begin to form, and the nuclear membrane dissolves.

How are chromosomes arranged during metaphase?

During metaphase, spindle fibers align the chromosomes along the equator of the cell, with each sister chromatid on opposite sides.

What is the role of spindle fibers in anaphase?

In anaphase, spindle fibers shorten and separate the sister chromatids at their centromeres, pulling them toward opposite poles of the cell.

How does telophase differ from the other phases of mitosis?

In telophase, a nuclear membrane reforms around each set of chromosomes, which then disperse into chromatin. The nucleolus also becomes visible again, marking the end of mitosis.

What is cytokinesis, and how does it differ between animal and plant cells?

Cytokinesis is the division of the cytoplasm. In animal cells, it occurs through the inward pinching of the cell membrane, while in plant cells, a cell plate forms along the equator, eventually developing into a new cell wall.

Why can't plant cells undergo cytokinesis through the same mechanism as animal cells?

Plant cells have a rigid cell wall that prevents the inward pinching of the cell membrane, so they form a cell plate to divide the cytoplasm.

What are centrioles, and how do they differ from centromeres?

Centrioles are structures at the poles of the cell where spindle fibers originate. Centromeres are the regions on chromosomes where sister chromatids are attached.

What is the end result of the M phase of the cell cycle?

The M phase results in the formation of two identical daughter cells, each with a complete set of chromosomes, identical to the original cell.