Ch 9 - cell signaling

Steps in cell signaling

1. Receptor activation

2. Signal transduction

3. Cellular response

4. Termination

Receptor activation def

signal binds to a receptor - which is then activated

Water soluble signal

Binds to receptor on membrane surface (polar so can’t get through nonpolar tails)

Lipid soluble signal

Can go inside cytoplasm - binds to receptor in the cell

Endocrine signaling

• for long distance traveling

• hormones = very stable

• specialized endocrine cell releases hormones —> go into blood stream —> travel through circulatory system to reach target cells

Paracrine signaling

• local signaling

• signaling molecules move from one cell to another through diffusion

• signals usually small & water soluble

Growth factor

• example of paracrine signaling molecules

• causes responding cell to grow, divide, or differentiate

Kohler and Lipton experiment hypothesis

since cells grow better in serum (clotted blood), growth factors come from platelets

Kohler & Lipton experiment 1 explain

• two dishes of fibroblasts cells —> one grown in plasma (unclotted) and one grown in serum (clotted)

  • result = fibroblasts in serum divided more rapidly

Kohler & Lipton experiment 2 explain

• fibroblasts grown in presence of platelet PROTEINS divided more rapidly than those grown in plasma

Kohler & Lipton Conclusion ****

Growth promoting factor = protein released by platelets on clot formation

• normally present in serum but not plasma

Synaptic signaling

• nerve cell releases neurotransmitters —> diffuse through synapse —> stimulate target cell (muscle or another nerve cell)

Autocrine signaling

• signaling and responding cell are one & same

• important for development of multicell embryo - developmental decision

Contact dependent signaling

• transmembrane protein in one cell acts as a signal —> binds to receptor protein on adjacent cell

Explain the process of ligand binding to receptor

• ligand binds to ligand-binding site

  • highly specific

• binding of ligand usually results in shape conformation of the receptor

  • this activates the receptor - how message is passed

Cell surface receptor

• for polar signaling molecule (water soluble)

• receptor has extracellular, transmembrane & cytoplasmic domain (transmembrane protein)

• when signal binds = entire molecule shape change

Intracellular receptor

• for small, non polar signals (lipid soluble)

• receptor inside cell

• ex) hormones - endocrine signaling

3 types of cell surface receptors

1. G protein coupled receptors

2. Receptor kinases

3. Ligand gated ion channel