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Cell Communication
CHAPTER 11
What you should know:
 The 3 stages of cell communication: reception, transduction,
and response.
 How G-protein-coupled receptors receive signals and start
transduction.
 How receptor tyrosine kinase receive cell signals and start
transduction.
 How a cell signal is amplified by a phosphorylation cascade.
 How a cell response in the nucleus turns on genes while in
the cytoplasm it activates enzymes.
 What apoptosis means and why it is important to normal
functioning of multicellular organisms.
Cell Signaling
Animal cells communicate by:
 Direct contact (gap junctions)
 Secreting local regulators
(growth factors,
neurotransmitters)
 Long distance (hormones)
Lipid Soluble
Second Animation
3 Stages of Cell Signaling:
1. Reception: Detection of a signal molecule
(ligand) coming from outside the cell
2. Transduction: Convert signal to a form that
can bring about a cellular response
3. Response: Cellular response to the signal
molecule
Reception
Transduction
Response
1. Reception
 Binding between signal molecule (ligand) +
receptor is highly specific.
 Receptors found in:
a) Intracellular receptors (cytoplasm, nucleus)
 hydrophobic or small
 Eg. testosterone or nitric oxide (NO)
b) Plasma membrane receptor
 water-soluble ligands
Plasma Membrane Receptors
G-Protein
Coupled
Tyrosine Kinase
Receptor (GPCR)
7 transmembrane
segments in
membrane
Attaches (P) to
tyrosine
G protein + GTP Activate multiple
activates enzyme cellular responses
 cell response
at once
Ligand-Gated
Ion Channels
Signal on receptor
changes shape
Regulate flow of
specific ions
(Ca2+, Na+)
G-Protein-Coupled Receptor
G-Protein-Coupled Receptor
Receptor Tyrosine Kinase
Ligand-Gated Ion Channel
Animation for G protein ion channel
2. Transduction
 Cascades of molecular interactions relay
signals from receptors  target molecules
 Protein kinase: enzyme that
phosphorylates and activates proteins at
next level
 Phosphorylation cascade: enhance and
amplify signal
Second Messengers
 small, nonprotein molecules/ions that can relay
signal inside cell
 Eg. cyclic AMP (cAMP) and Ca2+
Fig. 11-15
Reception
Binding of epinephrine to G protein-coupled receptor (1 molecule)
Transduction
Amplification
Animation 2
Inactive G protein
Active G protein (102 molecules)
Inactive adenylyl cyclase
Active adenylyl cyclase (102)
ATP
Cyclic AMP (104)
Inactive protein kinase A
Active protein kinase A (104)
Inactive phosphorylase kinase
Active phosphorylase kinase (105)
Inactive glycogen phosphorylase
Active glycogen phosphorylase (106)
Response
Glycogen
Glucose-1-phosphate
(108 molecules)
3. Response
 Regulate protein synthesis
by turning on/off genes in
nucleus (gene expression)
 Regulate activity of proteins
in cytoplasm
An Example of Cell
Communication
Lipid Soluble Example
Cholera
 Toxin modifies G-protein
 Disease acquired by
drinking contaminated
water (w/human feces)
 Bacteria (Vibrio cholerae)
colonizes lining of small
intestine and produces
toxin
involved in regulating salt &
water secretion
 G protein stuck in active
form  intestinal cells
secrete salts, water
 Infected person develops
profuse diarrhea and could
die from loss of water and
salts
Viagra
 Used as treatment for erectile dysfunction
 Inhibits hydrolysis of cGMP  GMP
 Prolongs signal to relax smooth muscle in
artery walls; increase blood flow to penis
Effect of apoptosis during paw
development in the mouse