NEET BIOLOGY

Detailed explanation-1: -Internal regulators-proteins that respond to events inside a cell. External regulators-proteins that respond to events outside the cell.

Detailed explanation-2: -The internal regulators are proteins inside of the cell while external regulators are proteins outside of the cell. Internal regulators will determine if the internal state of the cell is ready for cell division or not. If it is, then it allows division to proceed. If it isn’t, then it blocks cell division.

Detailed explanation-3: -Internal regulators of the cell cycle consist of two formal, well-defined types: positive regulator molecules such as cyclins and cyclin-dependent kinases and negative regulator molecules such as Rb, p53 and p21.

Detailed explanation-4: -Positive Regulation of the Cell Cycle Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints. The levels of the four cyclin proteins fluctuate throughout the cell cycle in a predictable pattern.