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Chemical Signaling - Coggle Diagram
Chemical Signaling
Receptors:
Proteins with specific binding sites for signalling chemicals (
ligands
).
Ligands
Categories of Signalling Chemicals in Animals
Hormones: Long-distance via bloodstream (e.g., insulin).
Neurotransmitters: Short-distance across synapses (e.g., acetylcholine).
Cytokines: Immune signalling proteins (e.g., interleukins).
Calcium ions (Ca²⁺): Secondary messengers in many pathways.
Chemical Diversity of Hormones & Neurotransmitters
Hormone classes
Amines (e.g., epinephrine).
Proteins/peptides (e.g., insulin).
Steroids (e.g., testosterone).
Intracellular Receptors & Gene Expression
Steroid hormones (e.g., oestradiol, progesterone, testosterone) bind cytoplasmic receptors.
Activated receptor binds DNA → Promotes gene transcription.
Hormones travel via blood → affect distant target cells
Effects of Oestradiol & Progesterone
Oestradiol: Acts on hypothalamus → Stimulates GnRH secretion.
Progesterone: Acts on endometrial cells → Prepares uterus for pregnancy.
Neurotransmitters include
Amino acids (e.g., glutamate).
Peptides (e.g., endorphins).
Amines (e.g., dopamine).
Nitrous oxide (NO) (gas neurotransmitter).
Neurotransmitters diffuse across synapses → affect nearby neurons
Receptors
Transmembrane receptors: Bind hydrophilic ligands (e.g., peptide hormones).
Intracellular receptors: Bind hydrophobic ligands (e.g., steroid hormones).
Neurotransmitter Receptors & Membrane Potential
Binding opens Na⁺ channels → Depolarization → Nerve impulse
Acetylcholine receptor
(ligand-gated ion channel)
G Protein-Coupled Receptors (GPCRs)
Ligand binding activates G protein → Signal transmitted inside cell.
Many human receptors are GPCRs (e.g., vision, smell, hormone signalling).
Epinephrine (Adrenaline) Receptor Mechanism
Epinephrine binds GPCR → Activates G protein → cAMP produced.
cAMP acts as second messenger → Triggers cell response (e.g., glycogen breakdown).
Naming difference: “Adrenaline” (Latin), “Epinephrine” (Greek).
Tyrosine Kinase Receptors (Example: Insulin Receptor)
Insulin binds receptor → Tyrosine phosphorylation inside the cell.
Leads to movement of glucose transporter vesicles → Increases glucose uptake.
Signal Transduction Pathways
Ligand binding → Triggers intracellular signalling cascade → Cell response
Quorum Sensing in Bacteria
Bacteria use cell signalling to coordinate behavior based on population density.
Example:
Vibrio fischeri
produces bioluminescence when quorum is reached.
Positive vs. Negative Feedback in Cell Signalling
Positive feedback: Amplifies response (e.g., oxytocin in childbirth).
Negative feedback: Inhibits response to maintain balance (e.g., insulin regulating blood glucose).
Types of Chemical Signaling
