1. Chapter 11
Cell Communication

3. Concept 11.1: External signals are converted into responses within the cell
Signal-transduction
pathway

4. LE 11-2 Exchange of mating factors a factor Receptor a a a factor
Yeast cell,
mating type a
Yeast cell,
mating type a
Mating a a
New a/a cell
a/a

5. LE 11-3
Plasma membranes
Gap junctions
between animal cells
Plasmodesmata
between plant cells
Cell junctions
Cell-cell recognition

6. Local regulators - short distances Hormones - long-distance signaling
Paracrine signaling
Local regulator
diffuses through
extracellular fluid
Secretory
vesicle
Secreting
cell
Target cell
Local signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Neurotransmitter
diffuses across
synapse
Endocrine cell
Blood
vessel
Long-distance signaling
Hormone travels
in bloodstream
to target cells
Synaptic signaling
is stimulated
Hormonal signaling
Target

7. The Three Stages of Cell Signaling: A Preview
Cells receiving signals go through three processes:
Reception
Transduction
Response
Animation: Overview of Cell Signaling

8. LE 11-5_1 EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception
Transduction
Receptor
Signal
molecule

9. Relay molecules in a signal transduction
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane
Reception
Transduction
Receptor
Relay molecules in a signal transduction
pathway
Signal
molecule

10. Relay molecules in a signal transduction
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane
Reception
Transduction
Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction
pathway
Signal
molecule

11. Concept 11.2: Reception: A signal molecule binds to a receptor protein, causing it to change shape
Ligand
Binding is highly specific
Conformational change

12. LE 11-6 Hormone EXTRACELLULAR (testosterone) FLUID The steroid
hormone testosterone
passes through the
plasma membrane.
Plasma
membrane
Testosterone binds
to a receptor protein
in the cytoplasm,
activating it.
Receptor
protein
Hormone-
receptor
complex
The hormone-
receptor complex
enters the nucleus
and binds to specific
genes.
DNA
mRNA
The bound protein
stimulates the
transcription of
the gene into mRNA.
NUCLEUS
New protein
The mRNA is
translated into a
specific protein.
CYTOPLASM

13. Receptors in the Plasma Membrane
There are three main types of membrane receptors:
G-protein-linked receptors
Receptor tyrosine kinases
Ion channel receptors

14. G-protein-linked receptor
LE 11-7aa
Signal-binding site
Segment that
interacts with
G proteins
G-protein-linked receptor

15. LE 11-7b Signal molecule Signal-binding site a Helix in the membrane
Tyrosines
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
Dimer
CYTOPLASM
Activated relay
proteins
Cellular
response 1
Tyr
Tyr P
Tyr P
Tyr P
Tyr
Tyr P
Tyr
Tyr P
Tyr
Tyr P P P
Tyr
Tyr
Tyr
Tyr P
Tyr
Tyr P P
Tyr
Tyr P
Cellular
response 2 6
ATP
6 ADP
Activated tyrosine-
kinase regions
(unphosphorylated
dimer)
Fully activated receptor
tyrosine-kinase
(phosphorylated
dimer)
Inactive
relay proteins

16. LE 11-7c Signal molecule (ligand) Gate closed Ions Plasma membrane
Ligand-gated
ion channel receptor
Gate open
Cellular
response
Gate closed

17. Transduction usually involves multiple steps Can amplify a signal
Concept 11.3: Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell
Transduction usually involves multiple steps
Can amplify a signal
More opportunities for coordination and regulation

18. LE 11-8 Signal molecule Receptor Activated relay molecule Inactive
protein kinase 1
Active
protein
kinase 1
Inactive
protein kinase 2
ATP
ADP
Active
protein
kinase 2 P
Phosphorylation cascade PP P i
Inactive
protein kinase 3
ATP
ADP
Active
protein
kinase 3 P PP P i
Inactive
protein
ATP
ADP P
Active
protein
Cellular
response PP P i

19. Small Molecules and Ions as Second Messengers
Second messengers are small, nonprotein, water-soluble molecules or ions
Cyclic AMP (cAMP)
cAMP
ATP
Second
messenger
First messenger
(signal molecule
such as epinephrine)
G-protein-linked
receptor
G protein
Adenylyl
cyclase
Protein
kinase A
Cellular responses
GTP

20. LE 11-10 First messenger (signal molecule such as epinephrine)
cAMP
ATP
Second
messenger
First messenger
(signal molecule
such as epinephrine)
G-protein-linked
receptor
G protein
Adenylyl
cyclase
Protein
kinase A
Cellular responses
GTP

21. Calcium ions and Inositol Triphosphate (IP3)
Calcium ions (Ca2+) act as a second messenger in many pathways
ATP
EXTRACELLULAR
FLUID
Mitochondrion
Ca2+
pump
Plasma
membrane
CYTOSOL
Endoplasmic
reticulum (ER)
High [Ca2+]
Key
Nucleus
Low [Ca2+]

22. Concept 11.4: Response: Cell signaling leads to regulation of cytoplasmic activities or transcription
“output response”
cytoplasm
nucleus
Many pathways regulate the activity of enzymes

23. LE 11-13
Reception
Binding of epinephrine to G-protein-linked receptor (1 molecule)
Transduction
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)

24. Transcription factor Growth factor Reception Receptor Phosphorylation
cascade
Transduction
CYTOPLASM
Inactive
transcription
factor
Active P
Response
Gene
mRNA
DNA
NUCLEUS

25. Signaling Efficiency: Scaffolding Proteins and Signaling Complexes
Scaffolding proteins can increase the signal transduction efficiency
Signal
molecule
Plasma
membrane
Receptor
Scaffolding
protein
Three
different
kinases