Control of cell growth, division and survival

Extracellular Signals

Required for cells to survive, grow, and divide; signals from other cells, mostly soluble proteins that are either secreted or bound to the surface of other cells.

Mitogens

Secreted signal proteins that bind cell-surface receptors and release the molecular 'brakes' that block progression to the S phase.

Platelet-derived growth factor (PDGF)

An example of a mitogen that binds a receptor tyrosine kinase on undamaged cells to stimulate proliferation for wound healing.

Hepatocyte growth factor

Stimulates liver cells to proliferate if they have been injured.

Growth Factors

Stimulate cell growth (size and mass), promote synthesis of macromolecules, and inhibit degradation of macromolecules.

Apoptosis

Regulates animal cell numbers through programmed cell death, removing cells that are not needed.

Caspases

Proteases made as inactive precursors, activated in response to signals that induce apoptosis.

Initiator caspases

Cleave and activate executioner caspases.

Executioner caspases

Disassemble key proteins in the cell, targeting lamin proteins which form the nuclear lamina.

Bcl2 Proteins

Regulate activation of caspases, promoting or inhibiting caspase activation and cell death.

Cytochrome c Activity

Induces cell death and is involved in the formation of the apoptosome, which recruits and activates the initiator caspase.

Extrinsic Apoptotic Death Program

Involves death receptors that receive apoptotic signals from other cells, triggering a caspase cascade.

Survival Factors

Suppress apoptosis and promote cell survival, ensuring a cell only survives when and where it is needed.

Inhibitory Signals

Extracellular proteins that inhibit cell survival, division, or growth, such as myostatin.

Myostatin

Inhibits growth and proliferation of myoblasts that fuse to form skeletal muscle cells during embryonic development.

Phenobarbital

A drug that stimulates liver cell division, allowing the liver to return to its normal size after tissue loss.

Apoptosome

A large seven-armed, pinwheel-like protein complex that recruits and activates the initiator caspase.

Death receptor

Cell-surface receptor that receives apoptotic signals from other cells, such as the Fas receptor.

Fas ligand

A membrane-bound protein that activates the death receptor Fas, inducing apoptosis in unwanted immune cells.

Bax and Bak proteins

Proteins that promote cell death in response to DNA damage by releasing cytochrome c from the mitochondria.

Webbing between toes

An example of cells removed during development through apoptosis.

Liver cells

Example of cells that proliferate to replace lost tissue when a piece of liver is removed.

Cell cycle control system

The system that regulates the progression of cells through the cell cycle, which growth factors can influence.