Cell signaling (Key Terms)

growth factor

(1) A protein that must be present in the extracellular environment (culture medium or animal body) for the growth and normal development of certain types of cells. (2) A local regulator that acts on nearby cells to stimulate cell proliferation and differentiation.

G protein

A GTP-binding protein that relays signals from a plasma membrane signal receptor

nitric oxide (NO)

A gas produced by many types of cells that functions as a local regulator and as a neurotransmitter. So small that it is able to diffuse through plasma membrane.

ligand

A molecule that binds specifically to another molecule; often first step in cell communication. Water soluble ligands typically do not enter cell. Lipid soluble ligands (such as steroids) do enter the cell.

apoptosis

A program of controlled cell suicide, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die.

ligand-gated ion channel

A protein pore in cellular membranes that opens or closes in response to A signaling chemical (its ligand), allowing or blocking the flow of specific ions.

receptor tyrosine kinase

A receptor protein 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 protein. It often responds to the binding of a signaling molecule by dimerizing and then phosphorylating a tyrosine on the cytoplasmic portion of the other receptor in the dimer. The phosphorylated tyrosines on the receptors then activate other signal transduction proteins within the cell.

transcription factor

A regulatory protein that binds to DNA and affects transcription of specific genes. The hormone-receptor complex becomes a transcription factor in the steroid transduction pathway.

diacylglycerol (DAG)

A second messenger produced by the cleavage of a certain kind of phospholipid in the plasma membrane.

inositol trisphosphate (IP3)

A second messenger that functions as an intermediate between certain nonsteroid hormones and a third messenger, a rise in cytoplasmic Ca2+ concentration.

local regulator

A secreted molecule that influences cells near where it is secreted. Used in paracrine and synaptic signaling.

phosphorylation cascade

A series of enzyme-catalyzed phosphorylation reactions commonly used in signal transduction pathways to amplify and convey a signal inward from the plasma membrane.

signal transduction pathway

A series of steps linking a mechanical or chemical stimulus to a specific cellular response. There are four types that we studied: g-protein linked reception; hormonal reception; receptor tyrosine kinase reception; pathways using second messengers (cAMP; calcium ions).

second messenger

A small, nonprotein, water-soluble molecule or ion, such as a calcium ion (Ca2+) or cyclic AMP, that relays a signal to a cell's interior in response to a signaling molecule bound by a signal receptor protein.

voltage gated ion channel

A specialized ion channel that opens or closes in response to changes in membrane potential

testosterone

A steroid hormone required for development of the male reproductive system, spermatogenesis, and male secondary sex characteristics; the major androgen in mammals. Pathway illustrates the mechanism for all steroid hormones.

gap junction

A type of intercellular junction in animals that allows the passage of materials between cells.

scaffolding protein

A type of large relay protein to which several other relay proteins are simultaneously attached, increasing the efficiency of signal transduction.

first messenger

A water soluble hormone that binds to its receptor at the outer surface of the plasma membrane.

adenylyl cyclase

An enzyme that converts ATP to cyclic AMP in response to a signal.

protein phosphatase

An enzyme that removes phosphate groups from (dephosphorylates) proteins, often functioning to reverse the effect of a protein kinase.

protein kinase

An enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein.

glycogen

An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.

plasmodesmata

An open channel in the cell wall of plants through which strands of cytosol connect from adjacent cells- present inside cell during cell junction type communication.

Hormone

Chemical messengers, mostly those manufactured by the endocrine glands, that are produced in one tissue and affect another

connexins

Gap junction proteins; a family of structurally-related transmembrane proteins that assemble to form gap junctions. Prevent cytoplasmic mixing. Exchange materials and electrical impulses. Somewhat like closely aligned channel proteins.

Reception

In cellular communication, the target cell's detection (by binding to a receptor protein) of a signal molecule from outside the cell.

Paracrine signaling

Local mediator, a secreting cell acts on nearby target cells by discharging molecules of a local regulator into the extracellular fluid

synapse

Location at which a neuron can transfer an impulse to another cell

intracellular receptors

Receptors within the cytosol that bind steroid hormones and some amino acid-derived hormones. Once bound, the hormone-receptor complex enters the nucleus where it alters gene expression.

yeast

Single-celled fungus that reproduces asexually by binary fission or by the pinching of small buds off a parent cell; some species exhibit cell fusion between different mating types.

cytoplasm

The contents of the cell, exclusive of the nucleus and bounded by the plasma membrane.

signal transduction

The linkage of a mechanical, chemical, or electromagnetic stimulus to a specific cellular response.

amplification

The strengthening of stimulus energy during transduction.

cellular response

Third stage of cell signalling; the signal exerts its effects by altering the activity of enzymes, altering the functions of structural proteins, or changing the expression of genes

Dimer

a compound whose molecules are composed of two identical monomers

cyclic AMP

a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells. It is also a regulator of some bacterial operons; cyclic adenosine monophosphate

Phosphodiesterase

an enzyme that breaks a phosphodiester bond in an oligonucleotide.

membrane receptors

bind to insulin and peptides -binds to receptor on membrane that activates enzyme which turns ATP into cyclic AMP - activates "2nd messenger" which leads to "Biochemical Cascade"

synaptic signaling

electrical signal along a nerve cell releases chemical signal in form of neurotransmitters and stimulates a cell across synapse

g-linked protein receptor

receives message for g-linked protein signaling pathway. Consists of seven alpha helices that span the plasma membrane. Changes shape when ligand molecule binds.

three stages of cell communication

reception - receptor responds to binding of ligand molecule; transduction - translation and amplification of message; response - activation of cellular response

epinephrine

water soluble ligand molecule; A catecholamine that, when secreted by the adrenal medulla, mediates "fight-or-flight" responses to short-term stresses; also released by some neurons as a neurotransmitter; also known as adrenaline.