Final answer:
The two signal categories driving the cell division cycle are external growth factors, which bind to cell-surface receptors to initiate cell division, and internal regulatory proteins like cyclins, Cdks, and tumor suppressor genes which govern the cell cycle's checkpoints.
Step-by-step explanation:
The two categories of signals that can drive the cell through the cell division cycle are external growth factors and internal regulatory proteins. External signals include growth factors that bind to cell-surface receptors and initiate a cascade of signaling pathways such as the MAP kinase pathway. Internal signals involve proteins that regulate cell cycle progress, such as cyclins and cyclin-dependent kinases (Cdks), as well as proteins encoded by proto-oncogenes and tumor suppressor genes. Cyclins and Cdks work together to advance the cell cycle at critical checkpoints, ensuring that the cell is ready for processes like DNA replication and mitosis. On the other hand, tumor suppressor proteins can halt the cell cycle if there are issues such as DNA damage or if the cell is in contact with other cells (contact inhibition), thereby preventing the inappropriate proliferation that can lead to cancer.