PATHOLOGY

Detailed explanation-1: -Cyclins are proteins that regulate the timing of the cell cycle in eukaryotic cells. Regulatory proteins are proteins that control the cell cycle both inside and outside of the cell. Internal regulators allow the cell cycle to proceed when certain events have occurred INSIDE a cell.

Detailed explanation-2: -Proteins that respond to events outside the cell are called external regulators. External regulators direct cells to speed up or slow down the cell cycle.

Detailed explanation-3: -The best-understood inhibitory signal proteins are TGF- and its relatives. TGF- inhibits the proliferation of several cell types, either by blocking cell-cycle progression in G1 or by stimulating apoptosis.

Detailed explanation-4: -Cyclins drive the events of the cell cycle by partnering with a family of enzymes called the cyclin-dependent kinases (Cdks).