chemical signalling

Vocabulary flashcards covering chemical signalling molecules, quorum sensing in bacteria, receptor types, neurotransmitter and hormone diversity, GPCR pathways, feedback mechanisms, and intracellular gene activation.

Receptor Protein

A protein that detects and responds to specific signals when bound to a signalling molecule or ligand.

Ligand

A chemical signalling molecule that binds to a specific site on a receptor, causing the receptor to change shape and activate an intracellular response.

Quorum Sensing

A system used by bacteria to coordinate group behaviors through the release and detection of chemical signalling molecules called autoinducers.

Autoinducers

Small chemical signals released by bacteria that diffuse freely in the environment, reaching a concentration threshold as population density increases to trigger changes in gene expression.

Luciferase

An enzyme produced in V. fischeri bacteria through autoinducer-receptor gene activation that causes a chemical reaction emitting light, with $80\%$ of energy released as visible light.

Hormones

Chemical signals secreted by endocrine glands directly into the bloodstream.

Neurotransmitters

Chemical signals used by neurons to communicate across a synapse.

Cytokines

Small proteins that control immune response, inflammation, and cell signalling.

Calcium Ions

Ions that function as secondary messengers in cellular signalling pathways.

Amine Hormones

Water-soluble hormones derived from amino acids that produce rapid, short-term physiological effects.

Steroid Hormones

Lipid-soluble hormones derived from cholesterol that pass through all cell membranes to bind with receptors and exert long-lasting effects.

Nitric Oxide

A gaseous neurotransmitter that diffuses across cell membranes without binding to traditional receptors.

Transmembrane Receptors

Receptors located in the cell membrane that bind to hydrophilic ligands unable to cross the lipid bilayer, inducing conformational changes in the receptor.

Intracellular Receptors

Receptors located inside the cell that feature hydrophilic amino acids on their surface to remain soluble in aqueous solutions while binding hydrophobic ligands that diffuse through the bilayer.

Signal Transduction Pathway

A three-step cascade consisting of Reception (ligand binds receptor), Transduction (signal relayed through intracellular molecules), and Response (cell performs a specific action).

Acetylcholine Receptor

A ligand-gated ion channel transmembrane receptor that changes shape when acetylcholine binds, allowing positively charged $Na^+$ ions to flow into the cell and depolarize the cell membrane.

G-Protein Coupled Receptors (GPCRs)

A family of transmembrane receptors that detect extracellular signals and undergo a conformational change to activate intracellular G-proteins by exchanging GDP for GTP.

Epinephrine

A hormone and neurotransmitter produced by the adrenal glands during stress or excitement (adrenaline) that promotes fight-or-flight responses via adrenergic GPCRs.

Adenylyl Cyclase

An enzyme activated by the $\alpha$ subunit of an activated G-protein that converts ATP into cyclic AMP (cAMP).

Cyclic AMP (cAMP)

A second messenger that relays and amplifies signals from the cell surface to the cell interior, diffusing through the cytoplasm to activate protein kinase A (PKA).

Protein Kinase A (PKA)

An enzyme activated by cAMP that adds phosphate groups to other target proteins within the cell.

Positive Feedback

A control mechanism where a cellular response strengthens the original signal, such as the LH surge and oestradiol release during the menstrual cycle.

Negative Feedback

A control mechanism where a cellular response counteracts the original signal, such as elevated testosterone decreasing LH to reduce testosterone production.

Tyrosine Kinase Receptors

Transmembrane receptors with an enzyme domain capable of phosphorylating tyrosine residues to initiate an intracellular signalling cascade.

Insulin Signalling

A pathway initiated by insulin binding to a plasma membrane receptor, leading to tyrosine phosphorylation and the movement of vesicles containing glucose transporters to the plasma membrane.

Oestradiol

A steroid hormone that diffuses through the plasma membrane of hypothalamic cells and binds to internal receptors that bind DNA to promote gene transcription.

Progesterone

A steroid hormone that thickens the uterine lining and inhibits uterine contractions, forming a hormone-receptor complex that enters the nucleus to act as a transcription factor for mRNA production.