C2.1 Chemical Signaling

Receptors

Proteins with binding sites for specific signaling chemicals.

Quorum Sensing

A process where cells secrete signaling molecules until a threshold concentration is reached, leading to changes in gene expression.

Ligand

Small molecules that transmit signals between or within cells.

Hormones

Signaling chemicals transported by bloodstream secreted by endocrine glands.

Neurotransmitters

Chemicals that transmit signals across synapses in the nervous system.

Cytokines

Small proteins that act as signaling chemicals, usually acting on the cell that produced them or nearby cells.

Calcium Ions

Used in cell signaling to trigger muscle contraction by binding to proteins after a nerve impulse opens calcium ion channels.

Localized vs Distant effects

Neurotransmitters are transported short distances, while hormones are transported through the bloodstream all over the body.

G-Protein Coupled Receptor (GPCR) Pathway

A signaling pathway where a ligand binds to GPCR, activates a G-protein, leading to a signaling cascade.

Subunits of G-Protein

Alpha, beta, gamma

Inactive G-Protein

GDP bound to alpha subunit

Active G-Protein

After Ligand binds to the receptor, GDP is replaced by GTP at alpha subunit to activate the G-protein

How does GPCR respond to signal?

G-protein separates into its 3 susbunits and dissociates from the receptor → triggers signaling cascade/cell response

What is the mechanism of Epinephrine receptors?

G-Protein Coupled Receptors

Adenylyl Cyclase (Epinephrine action)

Enzyme activated by active G-protein that converts ATP to cyclic AMP (cAMP)

Cyclic AMP (cAMP) (Epinephrine action)

Secondary messenger that amplifies the signal in the target cell

Kinase

Enzyme that adds phosphate from an ATP to a specific molecule (phosphorylation)

Receptor Tyrosine Kinases (RTK) Pathway

A signaling pathway activated when a ligand binds to RTK, leading to receptor dimerization and autophosphorylation.

What is the mechanism of Insulin receptors?

Receptor Tyrosine Kinase (RTK)

Insulin Action

Insulin binds to receptors leading to dimer formation and phosphorylation, triggering signal transduction.

Dimerization

The process where two receptor proteins bind together after ligand binding.

Second Messenger

Small molecules like cAMP that transmit signals inside the cell following receptor activation.

Transmembrane Receptors

Proteins that span the plasma membrane and are involved in signaling by binding ligands.

Signal Transduction Pathway (Hydrophobic Ligand)

Ligand directly passes through the membrane, binding to an intracellular receptor, and regulating gene expression.

How does the ligand-receptor complex regulate gene expression?

The Ligand-Receptor complex moves into the nucleus of the cell, attaching to a DNA strand and acting as a transcription factor.

Transcription Factor

A protein that binds to specific DNA sequences, regulating gene expression.

Testosterone

A steroid hormone that binds with androgen receptor to activate production of FADS1 gene.