Cell Communication
Chapter 11
11.1
External signals are converted to responses within a cell
Cells must “talk”
to coordinate
activities
 Evolved in single
and multicellular
organisms

◦ Ex: quorum sensing
in bacteria
◦ Ex: hormones in
plants and animals
Why cell communication?
Cell to cell
contact
 Local

◦ Paracrine
◦ Synaptic

Long distance
◦ Endocrine
Signaling by Distance

Receiving end of cell “conversation”
Signal Transduction Pathways
11.2
Reception: A signaling molecule binds to a receptor protein, causing it to change
shape
Chemical signal is
detected by the target
cell
 Surface proteins or
intracellular receptor
 Ligand

◦ Signaling molecule that
binds specifically to
another molecule
Reception



Ligand binds to G
protein-coupled
receptor on
membrane
G protein becomes
activated
Activated G protein
binds to enzyme,
activating it
G protein receptor is
COUPLED with G protein
Reception: G Protein-Coupled
Receptor

Ligand binds to
receptor tyrosine
kinase protein
monomers
◦ Kinase: enzyme that
transfers phosphate
groups


Activated
monomers form
dimer
Phosphates from
ATP added to
activated dimer
Reception: Receptor Tyrosine
Kinases
Ligand gated ion channel
changes shape when
ligand binds
 Opens “gate” so ions can
cross membrane

Reception: Ion Channel Receptors
Receptor in cytoplasm or
nucleus (NOT cell
membrane)
 Signal is hydrophobic or
small enough to cross
membrane

◦ Ex: steroid hormones, nitric
oxide
Reception: Intracellular Receptors
11.3
Transduction: Cascades of molecular interactions relay signals from receptors to
target molecules in the cell
Converts the signal to a form that the cell
can respond to
 Often involves relay molecules

Transduction
Series of proteins
activated by
addition of
phosphate group
pass signal along
 Like falling
dominoes

Transduction: Phosphorylation
Cascades

Non-protein messengers pass signal along
◦ Ex: cyclic AMP (cAMP), Ca+, or IP3
Transduction: Secondary
Messengers
11.4
Response: Cell signaling leads to regulation of transcription or cytoplasmic
activities
Specific response by
the cell
 Almost any
imaginable cellular
activity turned on or
off, depending on
signal
 Usually regulate
enzyme activity

Response

Genes turned on
to make proteins
◦ Activates
transcription

Genes turned off
to stop making
proteins
◦ Stops
transcription
Response: Nuclear

Proteins made are
modified, amplified,
or terminated
◦ Translation of genes
modified, resulting
proteins modified
Example: stimulation of glycogen
breakdown by epinephrine
Response: Cytoplasmic

Which receptors and secondary
messengers a cell has determines which
signals it will respond to and how
◦ Ex: liver and heart cells respond differently to
epinephrine
Cell Signaling Specificity
11.5
Apoptosis integrates multiple cell-signaling pathways
Programmed cell death
 Part of normal development and
differentiation

◦ Ex: formation of fingers and toes
◦ Ex: cancer cells

Complex cell signaling pathways
Apoptosis