Question

How is the cell cycle regulated?

Answer 1

The process involving replication of all the material present in the cell ultimately leading to the division of cells into two identical cells is known as the cell cycle.

Complete answer:
Various checkpoints present in the cell regulate the cell cycle at different stages. They can detect if there is any damage in the DNA of the cell thus inhibiting the replication of those cells. In the $G1$ stage of the cell cycle, a key checkpoint known as the Restriction point $\left( R \right)$is present. Most of the cells that can cross this restriction point will be able to complete the whole cell cycle. The transitions occurring in between $G1$ and S, and $G2$ and M also contain several other checkpoints.
The respective checkpoints are activated as soon as the damaged DNA is encountered. This increases the production of protein $p53$in the cells which being a tumor suppressor gene inhibits the progress of the cell cycle thus initiating the mechanism of repair in the damaged DNA. The DNA which cannot undergo repair mechanism endures apoptosis.
Cyclins also help in regulating the cell cycle thus controlling the progression of cell through activation of enzyme cyclin-dependent kinase$\left( {CDK} \right)$.

Note: Cell cycle comprises of four stages known as the G1 phase$\left( {Gap1phase} \right)$, S phase$\left( {SynthesisPhase} \right)$ , G2 phase $\left( {Gap2phase} \right)$ and M phase$\left( {MitosisPhase} \right)$. In eukaryotes, cells go through these stages as a part of their growth and division. Once the cycle is completed, the cell can restart its cycle from $G1$ or they exit through the $G0$phase thus undergoing termination.