Chapter 6 - Cell Signaling

Gap junctions

Tunnels called connexons connect neighbouring cells. Ions and small molecules can diffuse from the cytosol of one cell to the cytosol of another cell.

Connexins

Membrane proteins that form tunnels called connexons.

Cell-to-cell binding

A surface molecule on one cell binds to a surface molecule on another cell. Cells look linked

Target cell

Cell that can respond to the extracellular messenger

Signal transduction

Process by which the signal molecule is converted into a response by the target cell,

Signal transduction pathway

Sequence of events that occurs during signal transduction.

Extracellular chemical messenger

Molecule that is released by a cell, enters extracellular fluid (interstitial fluid and blood), and then binds to a receptor on or in its target cell to cause a response.

Hormones

Extracellular chemical messengers that are carried by the blood to distant target cells.

Glucagon

Hormone secreted by certain cells of the pancreas into interstitial fluid.

Endocrine signaling

Cell signaling that is mediated through hormones

Neurotransmitters

Extracellular chemical messengers that are released from a neuron into a synapse in order to reach a nearby target cell.

Synaptic signaling

Cell signalling that is mediated through neurotransmitters

Local mediators

Extracellular chemical messengers that act on nearby target cells without entering the bloodstream.

Paracrines

Local mediators that act on neighbouring cells

Autocrines

Local mediators that act on the same cell that secreted them

Local signaling

Cell signaling that occurs through local mediators.

Cytokines

Group of local mediators that regulate many cell functions like cell growth and differentiation.

Interleukin-2 (IL-2)

Cytokine that is released by helper T cells during immune response.

Nitric oxide (local mediator)

Local mediator that is released by endothelial cells lining blood vessels which causes relaxation of nearby smooth muscle fibres in blood vessels to cause vasodilation.

Eicosanoids

A molecule released by many cels in response to chemical or mechanical stimuli. They act as local mediators on nearby cells.

Arachidonic acid

20 carbon fatty acid that is made from a membrane phospholipid that is cleaved by the enzyme phospholipase A2.

Growth factors

Substances that play important roles in tissue development, growth, and repair.

Water-soluble extracellular messengers

Peptide or protein hormones (oxytocin), amine hormones (norepinephrine), nearly all neurotransmitters, eicosanoids, and growth factors that are soluble in water.

Lipid-soluble extracellular messengers

Steroid hormones (testosterone and estrogens), thyroid hormones, and nitric oxide that are soluble in lipids.

Agonist

Substance that binds to an activates a receptor, in the process mimicking the effect of the endogenous messenger.

Antagonist

Substance that binds to and blocks a receptor, thereby preventing the endogenous messenger from exerting its effect.

Plasma membrane receptors

Receptors that bind to water soluble extracellular messengers that are unable to pass through the interior of the plasma membrane. Present outside the cell.

Intracellular receptors

Receptors that bind to lipid-soluble extracellular messengers that are able to pass through the plasma membrane. Present inside the cell.

Down-regulation

Target-cell receptors decrease do to excess presence of extracellular messengers.

Up-regulation

Target cell increases the number of receptors when a messenger is deficient.

Signal transduction

The process by which a signal molecule (the messenger) is converted into a cellular response.

Signal transduction pathway or signalling pathway

Actions that cause a change in the effector protein of the cell which causes the cellular response

Effector protein

Protein that is changed that causes the cellular response in the signal transduction pathway.

Relay proteins

Proteins that convey the signal between the receptor and the effector protein.

Protein kinase

Enzyme that phosphorylates a target protein which activates or inhibits the target protein.