CHAPTER 11 cell signaling
I. Local regulators
Ex) growth factors – paracrine signaling
and neurotransmitters -synaptic signaling
II. Long distance signaling
- Hormones (insulin, ethylene)
- nervous system as a whole
3 stages of signaling
Earl Sutherland (1971) Epinephrine and
glycogen breakdown
1) Reception – binding to signal receptor
2) Transduction-often a series of changes (signal
transduction pathway)
3) Response-end result – a specific cellular
response
Receptor types
I. Bound to plasma membrane
G protein couple receptors
Receptor Tyrosine Kinases
Ion channel receptors
II. Intracellular
Located in cytosol or nucleus
-require hydrophobic or small messengers
Steroid hormones, thyroid hormones, NO
Membrane receptors up close
• G Protein-Coupled receptors
widespread, very common, involved with
many hormones (epinephrine), and embryonic
development
Involves G protein and GTP
1. G protein (cytoplasmic side) is off when bound
to GDP
2. Ligand binds to extracellular side of receptor
3. Receptor is actived (shape) and binds to G
protein
4. GTP replaces GDP on G protein
5. G protein binds to and activates an enzyme
6. G protein hydrolyzes GTP to GDP (GTPase) and
returns to start
Receptor Tyrosine Kinases
kinases transfer phosphate groups
Involved with enzymatic activity
Ex. Growth hormone binding/response
1. Individual receptor tyrosine kinase proteins
bind a signaling molecule (ligand)
2. Tyrosine kinase proteins form a dimer
3. This activates the kinase region of each, and
each tyrosine kinase phosphorylates its
tyrosines via ATP
4. Once activated, it is recognized by relay
proteins in cell and binds them
5. Often activates multiple pathways
Ion Channel Receptors
Involves gated responses involving ion flow
Ex) neurotransmitters (ligands) and
neurons(action potentials)
Ions flowing across membranes create currents
1. Ligand binds to channel receptor while
receptor is in closed conformation
2. Receptor changes shape to open gate
3. Very specific ion(s) begin to flow down their
electrochemical gradient
4. This flow of ions affects cell function
5. Ligand dissociates, ending the process
Intracellular receptor model
Results in gene expression (ex. Testosterone
effects)
1. Steroid hormone passes through plasma
membrane and binds to receptor protein in
cytoplasm
2. Activated receptor protein enters the nucleus
and acts as a transcription factor for a
particular gene