BIOS 1108 - Chemical and Electrical Signals - Principles of Chemical Signaling and Communication by Microbes (1)

Ligand

Chemical signal sent between cells; molecule that binds another specific molecule.

Hormones and neurotransmitters

Examples of ligands

Receptors

A protein in or on the target cell

Direct (Juxtacrine) Signaling

Communication between cells that are in direct contact with each other; often mediated by gap junctions in animal cells and plasmodesmata in plant cells.

Autocrine Signaling

Occurs when a ligand acts on the same cell that releases it.

Paracrine Signaling

Occurs when a ligand diffuses in a small area and only acts on neighboring cells.

Neural Signals

Specialized subset of paracrine signals, diffuses a very short distance within the synaptic cleft between adjacent neurons.

Endocrine Signals

Hormones which are carried throughout the organisms’s body via the vascular system (plants and animals) to act on cells that may be very far away from the cells which released the ligand.

Neuroendocrine Signals

A specialized subcategory of endocrine signals that are released by neurons but travel via the vascular system to act on cells that are far away.

Pheromones

Are released into the environment to act on the cells in a different individual.

Hydrophilic Hormones

Are soluble in water so they cannot cross the cell’s hydrophobic plasma membrane; receptor must be present on cell’s surface to reach it.

Peptide and Amino Acid-derived Hormones

Examples of hydrophilic hormones.

Hydrophobic Hormones

Small non polar molecules that are insoluble in water, can easily cross the cell’s hydrophobic plasma membrane; receptor located within cell’s cytoplasm or nucleus.

Steroid and Gas Hormones

Examples of hydrophobic hormones.

Signal Transduction

Process of converting a signal from one form to another; for hormone signaling, it converts an extracellular signal into an intracellular signal.

Second Messengers

Such as calcium or cyclic AMP which propagate throughout the cell to spread the signal

Phosphorylation Cascade

A series of proteins are activated by having a phosphate group added to them, changing their activity.

Signal Amplification

The signal form the hormone is amplified or magnified via several mechanisms.

Signal Amplification for Hydrophilic Hormones

Can occur via second messengers, thousands of molecules are produced or released in response to hormone signal; or through phosphorylation cascade, where thousands of proteins become activated.

Signal Amplification for Nonpolar Hormones

Can occur during the process of both transcription, where hundreds of copies of mRNA are synthesized from a single gene, and during translation, where hundreds of copies of each protein are synthesized from a single mRNA.

Positive Feedback Loop

Occurs when the response to a hormone causes the original signal to be amplified or increased. (Ex. Rock concert, musicians turn up the music causing the crowd to be more excited, making the musicians play louder, and increasing excitement in crowd. The signal has increased.)

Negative Feedback Loop

Occurs when response to a hormone causes the original signal to be decreased. (Ex. Temperature in room becomes too hot; heat causes thermostat to activate the AC, and the temperature becomes cooler. The signal decreased.)

Signaling Crosstalk

The outcome of a signal can change based on interactions between different signaling pathways. (Ex. When blood glucose is high, insulin causes muscle cells to take up the excess glucose to remove it from the blood; however, when adrenaline is also present, the insulin signaling pathway is blocked and muscle cells don’t take up excess glucose when adrenaline is present, even when insulin is also present.

Quorum Sensing

A phenomenon where individual single cells monitor the density of their population; one the population reaches a specific density, the cells collectively change their gene expression and behavior at the same time.

Autoinducer

What quorum sensing is based on; continuous secretion of a signaling molecule or a bacterial hormone.

Examples of Behaviors Controlled by Quorum Sensing

Symbiosis and bioluminescence, biofilm formation, and virulence.