1. Categorize chemical signals in terms of the proximity of the communicating cells.
Local signaling –
a. Paracrine signaling – a secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid.
b. Synaptic signaling – a nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.
Long distance signaling-
c. Hormonal signaling – specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells.
2. Describe the three main stages of cell signaling.
a. Reception – target cell’s detection of signaling molecule coming from outside the cell; chemical signal is “detected” when the signaling molecule binds to a receptor protein located at the cell’s surface or inside the cell.
b. Transduction – the signal is converted to a form that can bring about a specific cellular response.
c. Response – transduced signal triggers a specific cellular response. May be any imaginable cellular activity.
3. Describe a ligand-receptor interaction and state how such interactions initiate a signal-transduction system.
Ligand – receptor interaction: when a signaling molecule specifically binds as a ligand to the receptor protein, the gate opens or closes, allowing or blocking the flow of specific ions; protein interaction is a unifying theme of cell regulation at the cellular level.
4. Compare and contrast G-protein-linked receptors, tyrosine-kinase receptors, and ligand-gated ion channels.
G-protein linked receptors are signal receptor proteins in the plasma membrane that respond to the binding of a signaling molecule by activating a G-protein. Tyrosine-kinase receptors are receptor proteins in the plasma membrane, the cytoplasmic (intracellular) part of which can catalyze the transfer of a phosphate group from ATP to a tyrosine on another