Cyclins are the chemicals that regulate the cell cycle. They are part of the family of proteins. There are various types of cyclins, cyclin A, cyclin D, cylcin T, cyclin E and more.
A cell cycle's progress is generally hampered by two key issues, alternation and completion. Cyclin-dependent kinases or CDKs, which are enzymes, help in the solution of these issues. Cyclins attach themselves to CDKs and make them operative.
A cell's cycle is comprised of four phases, G1 and G2, which are gap phases, M phase and S phase. An example of cyclins' role is during the transition from G1 to S. Here cyclins E and D work on CDKs 4 and 2.