How the Cell Cycle Operates
GENETIC ENGINEERING: HOW THE CELL CYCLE OPERATES
A cell is a dynamic system. It is "born," lives, grows, reproduces, and dies. Each cell works like an automated factory, duplicating parts of it. It interacts with its environment, sending and receiving signals—electrical and chemical—to act on or cause action elsewhere, and guarding against invaders or aggressively attacking other cells. A cell changes shape, moves off to another place, and sometimes links up with other cells. There used to be two cell-cycle theories, called "domino" and "clock." The "domino" theory said that each event in the cell cycle was triggered by the event that occurred before it. In turn, it set off the next event, like a series of falling dominoes. The "clock" theory said that each event occurred at a preset time in the cycle. Scientists now know that the cell cycle progresses through a combination of domino and clock triggers. Cell-cycle events appear to take place within a certain time frame. But a chain reaction also occurs, and events are interdependent. The force that drives the cell cycle is a protein partnership between two kinds of chemicals called kinases and cyclins. The entire cell cycle is controlled by a set of genes called cell-division genes or cdc genes. Each cdc gene instructs the cell to produce a kinase needed to operate the cycle. The kinase-cyclin partnership is like a person who directs a movie and also stars in it. The partnership performs some operations itself and also controls the activity of proteins that perform other operations. Other genes are active at cell-cycle decision points, either letting the cycle go on or, if there are signs of a problem, stopping it in its tracks.
• Kinases Cell-cycle kinases are proteins (enzymes) formed by a gene named cdc2. They take phosphate groups from ATP (the cell's energy storehouse) and add them to proteins, activating the proteins for cell-cycle work, such as copying DNA for cell reproduction. The main methods of
A cell is a dynamic system. It is "born," lives, grows, reproduces, and dies. Each cell works like an automated factory, duplicating parts of it. It interacts with its environment, sending and receiving signals—electrical and chemical—to act on or cause action elsewhere, and guarding against invaders or aggressively attacking other cells. A cell changes shape, moves off to another place, and sometimes links up with other cells. There used to be two cell-cycle theories, called "domino" and "clock." The "domino" theory said that each event in the cell cycle was triggered by the event that occurred before it. In turn, it set off the next event, like a series of falling dominoes. The "clock" theory said that each event occurred at a preset time in the cycle. Scientists now know that the cell cycle progresses through a combination of domino and clock triggers. Cell-cycle events appear to take place within a certain time frame. But a chain reaction also occurs, and events are interdependent. The force that drives the cell cycle is a protein partnership between two kinds of chemicals called kinases and cyclins. The entire cell cycle is controlled by a set of genes called cell-division genes or cdc genes. Each cdc gene instructs the cell to produce a kinase needed to operate the cycle. The kinase-cyclin partnership is like a person who directs a movie and also stars in it. The partnership performs some operations itself and also controls the activity of proteins that perform other operations. Other genes are active at cell-cycle decision points, either letting the cycle go on or, if there are signs of a problem, stopping it in its tracks.
• Kinases Cell-cycle kinases are proteins (enzymes) formed by a gene named cdc2. They take phosphate groups from ATP (the cell's energy storehouse) and add them to proteins, activating the proteins for cell-cycle work, such as copying DNA for cell reproduction. The main methods of