What happens at each of the 3 cell cycle checkpoints.?

Cyclinany of a group of proteins that regulates the cell cycle by forming a complex with kinasesG2 checkpointensures all of the chromosomes have been replicated and that the replicated DNA is not damagedrestriction point(G1 checkpoint) a point in the animal cell cycle at which the cell becomes "committed" to the cell cycle, which is determined by external factors and signalsspindle checkpoint(M checkpoint) prevents separation of the duplicated chromosomes until each chromosome is properly attached to the spindle apparatus

A) 4 amusingb)alpha particle is a helium nucleus. it contains 2 protons and 2 neutrons.c)alpha particle has charge of +2.