Cell Cycle

CELL CYCLE

Cell cycle also known as cell-division is the series of events a cell undertakes to replicate all of its materials into two daughter cells. In this article, we will look at different stages of the cell cycle and what happens in each stage. Specifically discussing the eukaryotic cell cycle.  Cells with nuclei (eukaryotes), (i.e. animals, plant, fungal and protist cells). Cell without nuclei (prokaryotes), (i.e. Achaea, and bacteria).

PHASES OF THE CELL CYCLE

The eukaryotic cell consists of 4-stage process or phases:  Gap 1 (G₁ phase), S phase (synthesis), (G₂ phase) Gap 2 (known collectively as interphase), and M phase (Mitotic and cytokinesis). Participating eukaryotic cells undergo these steps as it grows and divides. Cell undergoes terminal differentiation from G_0. After completing the cycle, the cell either starts the process again from G₁ or exits the cycle through G_0.

·         G₀ or the resting phase

In G_0, a cell is performing its function without actively preparing to divide. At this point, some cell types are at rest and may exit G₁ and enter a resting state. While others may re-start division if they get the right signals.

·         G₁ phase

* Cell increases in size.

* Cellular contents duplicates and ready for DNA synthesis.

·         S phase (synthesis)

* In this phase, DNA replication occurs.

* Each of the 46 chromosomes is replicated by the cell (23pairs).

·         G₂ phase (interphase)

* The cell will begin to grow more during the gap between the S phase and M phase.

* In preparation for cell division, organelles and proteins develop.

·         M phase (mitotic)

* Cell separation occurs

* Formation of two identical daughter cells

REGULATION OF EUKARYOTIC CELL CYCLE

Each cell cycle is ordered and directional in a sequential fashion and it is impossible to “reverse” the cycle. It is controlled by checkpoints at different stages. The key checkpoint is located at G₁ known as the restriction point, it detects if a cell contains damaged DNA and ensures those cells do not replicate. Protein P⁵³ is a tumor suppressor gene that stops the progression of a cell cycle and initiates repair mechanisms for a damaged DNA example retinoblastoma protein (Rb). However, there is an increased protein P⁵³ production if there is a detection of a damaged DNA at any checkpoint. If the DNA cannot be repaired, then it ensures the cell undergoes apoptosis (cell death) and can no longer replicate.