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Chapter 11 notes
Cell Communication
The Cellular Internet
Trillions of cells in a multicellular
organism must communicate together
to enable growth, survival, and
reproduction
The same cell-signaling mechanisms tend
to show up again and again
Concept 11.1
Yeast cells use cell signaling to identify
mates
- two sexes, type a and type a
- cells secrete a chemical signal that
binds to receptors on the opposite cell
- causes the two cells to grow toward
each other so they can fuse and mate
Concept 11.1
Signal transduction pathway: process
by which a signal on a cell’s surface is
converted into a specific cellular
response
Concept 11.1
a factor
Receptor
1
Exchange
of mating
factors
2
Mating
3
New a/a
cell
a
a
a factor
Yeast cell,
Yeast cell,
mating type a
mating type a
a
a
a/a
Concept 11.1
Some cells communicate through direct
contact
- use of cell junctions
- animal cells use membrane-bound cell
surface molecules
Concept 11.1
Plasma membranes
Gap junctions
between animal cells
(a) Cell junctions
(b) Cell-cell recognition
Plasmodesmata
between plant cells
Concept 11.1
Some molecules only travel a short
distance
- local regulators (ex. growth factors)
Synaptic signaling is found in the
nervous system
- electrical signal triggers the release of
neurotransmitters across a synapse
Concept 11.1
Hormones are used for long-distance
signaling
- specialized cells release hormones into
the circulatory system to travel to other
parts of the body
Concept 11.1
Long-distance signaling
Local signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid
(a) Paracrine signaling
Endocrine cell
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Target cell
is stimulated
Blood
vessel
Hormone travels
in bloodstream
to target cells
Target
cell
(b) Synaptic signaling
(c) Hormonal signaling
Concept 11.1
The receiving end of a signal can be
organized into three stages:
Reception
- a chemical signal is bound to a
receptor protein at the cell’s surface
Transduction
- converts the signal to a form that can
produce a cellular response
Concept 11.1
Response
- any cellular activity that the cell is
directed to accomplish
Concept 11.1
Concept 11.1
Concept 11.1
Concept 11.2
Reception
- the receptor protein on a target cell
allows the cell to “hear” the message
from a signal
- the signal is complementary in shape
and attaches to the protein
- the receptor protein changes shape,
and thus is activated
Concept 11.2
Receptors can be intracellular or plasma
membrane bound
To reach the intracellular receptors,
messengers must be able to pass
through the plasma membrane (either
small or hydrophobic)
- ex. steroid hormones or NO (nitric
oxide)
Concept 11.2
Most water soluble molecules are going to
bind to plasma membrane receptors
- receptor transmits information from
the outside environment to the inside of
the cell
Concept 11.2
Plasma
membrane
G protein-coupled
receptor
Activated
receptor
Signaling molecule
GDP
CYTOPLASM
GDP
Enzyme
G protein
(inactive)
GTP
2
1
Activated
enzyme
GTP
GDP
Pi
Cellular response
3
4
Inactive
enzyme
Concept 11.3
Transduction
- usually a multi-step process
- benefit in that it greatly amplifies a
signal
Protein kinase: an enzyme that
transfers phosphate groups from ATP to
a protein
Concept 11.3
Signaling
molecule
Recepto
r
Activated relay
molecule
Inactive
protein kinase
1
Active
protein
kinase
1
Inactive
protein kinase
2
ATP
Pi
ADP
PP
Inactive
protein kinase
3
Pi
P
Active
protein
kinase
2
ATP
ADP
Active
protein
kinase
3
PP
Inactive
protein
ATP
Pi
PP
ADP
P
P
Active
protein
Cellular
respons
e
Concept 11.3
Many signaling pathways also involve
small, nonprotein molecules called
second messengers
- ex. cyclic AMP (cAMP) carries a
signal initiated by epinephrine from the
plasma membrane of a liver cell into the
cell’s interior
Concept 11.3
- the binding of epinephrine to a liver cell
activates adenlyl cyclase, which in
turn can synthesize many molecules of
cAMP
Concept 11.3
First messenger
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Second
messenger
Protein
kinase A
Cellular responses
Concept 11.4
Response
In the liver cells, the final step activates
the enzyme that catalyzes the
breakdown of glycogen into glucose
Many other signaling pathways regulate
the synthesis of an enzyme by turning
genes on and off
Concept 11.4
Signal Amplification
- at each step in the cascade, the
number of activated products is much
greater than the preceding steps
- b/c the proteins persist in an active
form long enough to process numerous
molecules
Concept 11.4
Specificity of Cell Signaling
- ex. heart cells vs. liver cells
- respond to some signals but ignore
others
- different responses to the same
signal (ex. epinephrine)