Cell cycle

Normal Cell Life Cycle

Wilson1900Fig2

File:Reconstitution in 6 phases, of the changes in cell shape (in red) and nucleoid structure (roughly equivalent to the DNA, in green), during the cell cycle of the bacteria D. radiodurans.webm

Cell Cycle 2-2

Plant cell cycle

Cell Cycle

The cell cycle is a complex series of stages that a cell undergoes as it grows and divides. A fundamental process in biology, it ensures that a cell duplicates its contents, including its DNA, and splits to form two daughter cells. The cell cycle is crucial for the growth and development of organisms, tissue repair, and reproduction in unicellular organisms. It is divided into two main phases: interphase and the mitotic phase (M phase).

Phases of the Cell Cycle

Interphase

Interphase is the phase of the cell cycle during which the cell prepares for division. It is subdivided into three phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2).

• G1 Phase: During this phase, the cell grows physically larger, copies organelles, and makes the molecular building blocks it will need in later steps.
• S Phase: In the synthesis phase, the cell synthesizes a complete copy of the DNA in its nucleus. This is a crucial step leading to cell division.
• G2 Phase: During the G2 phase, the cell continues to grow and makes any necessary repairs to the DNA. The cell checks to ensure all the DNA is replicated and repairs any damaged DNA before moving into the mitotic phase.

Mitotic Phase

The mitotic phase is where the cell divides its copied DNA and cytoplasm to make two new cells. This phase can be further divided into two processes: mitosis and cytokinesis.

• Mitosis: Mitosis is the process by which the cell nucleus divides. It is itself divided into stages: prophase, prometaphase, metaphase, anaphase, and telophase. During these stages, the chromosomes condense, align in the middle of the cell, and are pulled apart to opposite ends of the cell.
• Cytokinesis: Cytokinesis is the division of the cell's cytoplasm, resulting in two daughter cells. In animal cells, this involves the formation of a cleavage furrow that pinches the cell in two. In plant cells, a cell plate forms along the center line of the cell, eventually leading to the formation of a new cell wall.

Regulation of the Cell Cycle

The cell cycle is tightly regulated by a complex network of signaling pathways. Central to this regulation are cyclins and cyclin-dependent kinases (CDKs). These molecules ensure that cell cycle events occur in the correct sequence and at the correct time. Malfunctions in cell cycle regulation can lead to uncontrolled cell growth, a hallmark of cancer.

Cell Cycle Checkpoints

Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division. There are several key checkpoints:

• The G1 checkpoint ensures that the cell is ready for DNA synthesis.
• The S checkpoint ensures that DNA replication is complete and has not been damaged.
• The G2 checkpoint ensures that all DNA is replicated and repaired correctly.
• The M checkpoint ensures that all chromosomes are attached to the mitotic spindle before anaphase begins.

Conclusion

The cell cycle is a critical biological process that enables cells to grow, replicate their DNA, and divide. Its regulation is complex and involves numerous checkpoints and molecular signals. Understanding the cell cycle is essential for insights into various biological processes and diseases, including cancer.