Regulating the Cell Cycle

10-3

Controls on Cell Division

If we look at cells dividing in a petri dish we can see that they will divide until they cover the bottom of the dish

Controls on Cell Division

If we take out all of the cells in the middle of the dish, the other cells will divide until the plate is covered again, at which point cell division will stop occuring

Controls on Cell Division

This is similar to how the body heals

When the body is cut, broken, or bruised, cells at the edge of the injury are stimulated to divide rapidly

Controls on Cell Division

This stimulation is what creates the healing of the injury and restoration of the body

Cell Cycle RegulatorsIn the 1980’s two scientists, Tim Hunt of the UK and Mark Kirschner of the USA discovered that cells in mitosis contain a specific protein that stimulates Mitosis to occur

Cell Cycle RegulatorsThis protein is called Cyclin because it controls the cell cycle

They did an experiment where they injected cyclin which was found to stimulate the growth of spindles, causing mitosis to occur

CyclinThere are many different types of Cyclin proteins that are found in mitotic cells

Some are known as internal regulators while others are external regulators

Internal RegulatorsCyclin proteins that are internal regulators respond to events that are inside the cell

Examples would be cyclin that prevents a cell from entering anaphase until all its chromosomes are attached to spindles

External RegulatorsExternal Regulators are cyclin proteins that respond to events that are outside the cell

They direct cells to speed up or slow down the cell cycle

CancerCell growth and reproduction must be monitored carefully

If it is uncontrolled, cancer will form

Cancer cells do not respond to the signals that regulate most cells

Cancer

When a cancer replicates uncontrollably it will form a tumor which can harm surrounding tissue