I. Introduction

• The cell cycle is the sequence of events that a cell goes through as it grows and divides.
• These events can be broadly divided into two main stages: interphase (G1, S, G2) and the mitotic phase (M).
• The cell cycle is regulated by a complex network of molecular interactions, which ensure proper timing and coordination of the various events.

II. Interphase

A. G1 phase

• The G1 phase is the period of cell growth and metabolic activity.
• During this phase, the cell increases its mass and carries out necessary biosynthetic activities.
• The G1 checkpoint, also known as the restriction point, serves as a checkpoint for the cell to assess the availability of growth factors and nutrients, and to ensure proper DNA repair before proceeding to the S phase.

B. S phase

• The S phase is the period of DNA replication.
• During this phase, the cell replicates its DNA in preparation for cell division.
• The replication is carried out by a complex of proteins called the replisome, which includes helicases, primases, and polymerases.

C. G2 phase

• The G2 phase is the period of final growth and cell cycle checkpoint.
• During this phase, the cell carries out necessary biosynthetic activities and checks the integrity of the replicated DNA before proceeding to the mitotic phase.
• The G2 checkpoint, also known as the mitotic checkpoint, serves as a checkpoint for the cell to assess the proper replication and repair of DNA before initiating cell division.

III. Mitotic Phase

• The mitotic phase is the period of cell division, where the cell physically divides into two daughter cells.
• This phase is controlled by the activity of a variety of proteins, including kinases, phosphatases, and motor proteins.
• Key regulatory proteins include Cyclin-dependent kinases (CDKs) and their regulatory subunits, cyclins, which control the progression through the cell cycle.

IV. Conclusion

• The cell cycle is a complex and highly regulated process that involves a series of molecular interactions, which ensure proper timing and coordination of the various events.
• Understanding the molecular basis of the cell cycle is essential for the development of therapies for various diseases, including cancer, where cell cycle regulation is often disrupted.