Biology Unit 1: Part 4

Cell signals and responses

Cell transduction pathway

sequence of molecular events and reactions that lead to a cellular response

Short-term response changes

enzyme activation, cell movement

Long-term response changes

altered DNA transcription

4 Major types of cell signals

Juxtacrine, autocrine, paracrine, endrocrine

Juxtacrine signals

affect neighboring cells through direct contact (diffusion or gap junctions) (ions in nerve cells)

Autocrine signals

affect the same cells that release them (tumors)

Paracrine signals

signals diffuse to and affect nearby cells (neurotransmitter)

Endocrine signals

signals travel to distant cells (hormones)

Cytoplasmic receptors

have small nonpolar ligands that can diffuse across membrane

Membrane receptors

have large or polar ligands that must bind to a transmembrane receptor at an extracellular site

Receptor classes by activity

Ion channel receptors, protein kinase receptors, G protein-linked receptors

Ion channel receptors (gated ion channels)

change 3D shape when ligand bonds

Acetylcholine receptor

ligand-gated sodium channel in neurotransmitters, allows for muscle contractions

Protein kinase receptors

change 3D shape when ligand bonds → exposes or activates a cytoplasmic domain that has catalytic activity

Insulin

protein kinase that binds to its protein kinase receptor to allow glucose from blood cells into the cell through channel

Reaction that protein kinases catalyze

ATP + protein → ADP + phosphorylated protein

G protein-linked receptors

ligand binding → expose a site that can bind to membrane protein (G protein) → activated G protein-linked receptor exchanges a GDP nucleotide, that’s bound to the G protein, for GTP → activated G protein activates the effector protein → signal amplification

Secondary messenger

intermediary step between receptor and cascade of responses (cAMP in fight-or-flight response

cAMP

secondary messenger important in adrenaline response