3.01 - Principles of Chemical Signaling and Communication by Microbes

Direct signaling

Communication between adjacent cells via physical cytoplasmic junctions, such as plasmodesmata in plants and gap junctions in animals.

Autocrine signaling

A signaling mode in which a cell secretes chemical messengers that bind to receptors on its own surface, regulating its own activity.

Paracrine signaling

Local signaling in which a released ligand diffuses through extracellular fluid to act on neighboring target cells.

Endocrine signaling

Long-distance signaling where hormones are secreted into the bloodstream or vascular system to reach distant target tissues.

Neuroendocrine signaling

Communication in which specialized neurons convert electrical action potentials into chemical hormones released directly into the circulation.

Pheromones

Chemical signaling molecules released into the external environment that elicit physiological or behavioral responses in individuals of the same species.

Polypeptide hormones

Hydrophilic, polar chains of amino acids that cannot cross the plasma membrane and must bind to cell-surface receptors.

Steroid hormones

Small, hydrophobic, lipid-soluble molecules derived from cholesterol that diffuse across the plasma membrane to bind intracellular receptors.

Amino acid derivative hormones

Signaling molecules synthesized from single amino acids like tyrosine that are mostly hydrophilic and interact with cell-surface receptors.

Signal transduction

The multi-step molecular process through which an extracellular chemical signal is converted into a specific intracellular response.

Steroid hormone amplification mechanism

Signal multiplication achieved via repeated transcription of target genes into numerous mRNA copies and repeated translation of each mRNA into multiple proteins.

G-protein coupled receptor (GPCR) amplification mechanism

Receptor activation causes a G-protein to bind GTP and activate an enzyme, driving the rapid production of abundant second messenger molecules such as cAMP.

Enzyme-linked receptor amplification mechanism

Signal binding triggers receptor autophosphorylation and initiates a kinase cascade where each active enzyme phosphorylates multiple downstream substrates.

Negative feedback loop

A regulatory control system in which the biological response dampens the initial stimulus, restoring physiological parameters to a set-point to maintain homeostasis.

Positive feedback loop

A regulatory mechanism in which the downstream output enhances and reinforces the original stimulus, driving a process rapidly toward completion.

Crosstalk

The inter-pathway communication where components of one signal transduction cascade stimulate or inhibit an independent pathway to integrate multiple inputs.

Primary factors causing cell-specific hormone responses

Differential expression of receptor subtypes across tissues and variations in downstream intracellular relay proteins and target enzymes within distinct cell types.

Quorum sensing

A cell-density-dependent communication mechanism in bacteria where the concentration of secreted autoinducers coordinates group gene expression.

Biofilm

A surface-attached microbial community enclosed within a self-secreted matrix of extracellular polymeric substances, regulated by quorum sensing.