Cyclin A is a type of protein that plays a crucial role in regulating the cell cycle, particularly during the transition from the G1 phase to the S phase and the G2 phase to the M phase. It activates specific enzymes called cyclin-dependent kinases (CDKs), which are essential for cell division and growth. Cyclin A is involved in various cellular processes, including DNA replication and repair. Its levels fluctuate throughout the cell cycle, rising during the S phase and G2 phase and decreasing as the cell progresses into mitosis. Proper functioning of Cyclin A is vital for maintaining normal cell division and preventing cancerous growth.