The Cell Cycle and Mitosis

The Cell Cycle: Overview

The cell cycle is the regular sequence of events that occur in a cell leading to its division and duplication.
It consists of four primary phases: G1 (first gap), S (synthesis), G2 (second gap), and M (mitosis).
During the G1 phase, the cell increases in size in preparation for DNA replication.
In the S phase, DNA replication occurs, resulting in two identical sets of chromosomes.
The G2 phase is another period of growth and preparation for cell division.
The M phase involves the separation of the duplicated DNA into two new cells during the process of mitosis.

Mitosis: Stages and Functions

Mitosis is the division of a single cell’s nucleus into two identical daughter nuclei leading to the creation of two genetically identical cells.
Mitosis takes place in a series of steps: prophase, metaphase, anaphase, and telophase.
Prophase begins when the chromosomes condense and the nuclear membrane dissolves. The centrosome replicates and moves to opposite ends of the cell forming a mitotic spindle.
During metaphase, the chromosomes align along the equatorial plate or metaphase plate. Each chromosome connects to spindle fibres at its centromere.
In anaphase, the sister chromatids are separated and drawn to opposite ends of the cell due to the shortening of spindle fibres.
Telophase marks the final stage of mitosis, where each set of chromosomes is enclosed by a new nuclear envelope. The cell then undergoes cytokinesis to form two separate cells.
Mitosis plays a crucial role in growth, repair, and asexual reproduction.

Role of Checkpoints and Regulatory Proteins

The cell cycle is controlled by a series of checkpoints that ensure the process proceeds correctly.
The G1 checkpoint checks for cell size, nutrients, growth factors, and DNA damage.
The G2 checkpoint ensures that DNA replication has correctly occurred in the S phase.
The M checkpoint ensures that the chromosomes are properly aligned for separation.
Regulatory proteins such as cyclins and cdks are crucial for controlling the cell cycle transitions.

Implications of Errors in the Cell Cycle

Errors during the cell cycle can lead to mutations, uncontrolled cell growth, and ultimately cancer.
Cancer originates from a single cell that begins to divide and grow in an uncontrolled manner, bypassing all cell cycle checkpoints.

Appreciating the complexity of cell division allows a deeper understanding of how life continues and proliferates. Recognize the importance of each stage for cellular health and continuity.