The Cell Cycle and The Regulators Controlling Process

The cell cycle is the process in which a cell goes through leading to the duplication of its DNA and division to produce two daughter cells. It is a series of events that include interphase and mitosis. The interphase is composed of three sub sets, and is where the cell duplicates its DNA and grows in preparation for mitosis. Mitosis is the process where cell division occurs. To promote the cell cycle, phosphorylated cyclin and cyclin-dependent kinase complexes are used. They regulate the cell cycle and phosphorylate other proteins that furtherly promote the cycle.

The first interphase is gap phase one (G1 phase). During this phase the cell grows and prepares for DNA synthesis. The mitochondria respiration provides the energy for the growth.

After the G1 phase the cell goes through the first checkpoint, the restriction point. At this checkpoint, if there is damage to the DNA or other external factors it does not progress to the next phase. The negative regulator molecules (retinoblastoma protein, p53, and p21) are responsible for preventing the cell from moving to the next phase until the damaged DNA is repaired.

The second interphase is the synthesis phase (G2 phase). This is where the DNA duplication occurs, and all the chromosomes are replicated. DNA polymerase are used to synthesise the DNA molecules which are essential for duplication.

After synthesis, the cell goes through the S checkpoint. This checkpoint ensures that all the chromosomes and DNA that have been replicated are not damaged, so the cell can go further to the third interphase.

The final interphase is the gap two phase (G2 phase). During this phase the cell goes through further growth and preparation for mitosis. Biosynthesis occurs which involves the production of microtubules, which are required for the mitosis stage.

After going through the final interphase, the cell goes through the G2 checkpoint. This point verifies that the replicated DNA is not damaged and that all the chromosomes have been replicated. The cell is then suitable to go through the mitosis stage.

The mitosis stage is made up of three sub-stages, the prophase stage, the metaphase stage, the anaphase stage, and the telophase stage.

During prophase, mediated by condensin complex, the chromatin condenses into the structure of chromosomes. This process is called chromatin condensation. The condensed and coiled chromosomes then move onto the metaphase, where they align in the middle of the cell then separate into two daughter cells. The cell then goes through the M checkpoint, at this point whether the sister chromatids are correctly attached to the spindle microtubules is determined, if they are attached correctly the cell can then enter the anaphase. In the anaphase all the chromatids separate and align with the spindle fibres. Then in the telophase, the cell membrane forms, nucleoli appear, and all the other organelles. The two daughter cells are fully formed. The cycle continuously repeats.

There is an additional stage to the cell cycle called the G0 stage. This is known as the resting phase and some cells are resting in this phase which may be quiescence if they get a signal to divide or senescence. The cells in this stage are alive and carrying out their functions but are not preparing for division, they divide slowly or do not divide at all.