Download AP Cell Signaling

Cell Communication
Reception, Transduction,
Response
Local signals
• Cells in a multicellular organism communicate
by chemical messengers
• In local signaling, animal cells may
communicate by direct contact, or cell-cell
recognition
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Local signals cont’d
• local regulators - messenger molecules that travel
short distances
• Paracrine signaling – local regulator released directly
onto one cell by another
• Synaptic signaling – a nerve signal triggers the
release of a local regulator onto a near by cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Long Distance Signaling
• Hormones – chemical messengers that travel
long distance.
• Ex. Through blood vessels
Signal Transduction Pathway
• After a signal is received a signal transduction
pathway is a set of step that trigger a certain response
from a cell.
1 Reception
2 transduction
3 response**
• Ex. Yeast mating
Reception
• Reception – delivery of a signal to a cell
• Signal molecules are called ligands (ex.hormones)
• Water soluble ligands must bind to receptor proteins in
the cell membrane
• Non-polar or small ligands can travel directly in the cell
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G protein-coupled receptor
• G protein-coupled receptor – membrane receptor that
activates a G protein when a ligand is present. (starts
transduction)
• G protein – When activated, uses energy from GDP
becoming GTP to turn on an enzyme.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Receptor Tyrosine Kinase
• Receptor tyrosine kinase - membrane receptors that
attach phosphates to tyrosines.
• When the ligand is present the two kinases form a
dimer and can
trigger multiple
transduction
pathways.
Gated Ion Channels
• ligand-gated ion channel –
receptor opens like a gate
when a ligand is present
to allow ions in.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 11-7d
1 Signaling
molecule
(ligand)
Gate
closed
Ligand-gated
ion channel receptor
2
Ions
Plasma
membrane
Gate open
Cellular
response
3
Gate closed
Intracellular (internal) Receptors
• Small or hydrophobic ligands
travel directly through the cell
membrane.
• They join to an internal receptor
to form a hormone receptor complex
(which begins transduction)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Transduction
• Signal transduction usually involves multiple
steps that includes turning a sequence of
proteins on and off to get a response from
the cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Phosphorylation/Dephosphorylation
• Phosphorylation – add phosphates (turns protein on)
• Dedphosphorylation – removes phosphates (turns
proteins off)
• Protein kinases – does phosphorylation
• Protein phosphatases- does dephosphorylation
Phosphorylation Cascade
Second Messengers
• Second messengers – small molecules that diffuse
throughout the cell to carry the signal during
transduction.
• Second messengers,
cAMP (made from ATP),
IP3, Ca+, DAG**
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 11-13-2
EXTRACELLULAR
FLUID
Signaling molecule
(first messenger)
G protein
DAG
GTP
G protein-coupled
receptor
Phospholipase C
PIP2
IP3
(second messenger)
IP3-gated
calcium channel
Endoplasmic
reticulum (ER)
CYTOSOL
Ca2+
Ca2+
(second
messenger
)
Response
• Cell usually respond by synthesizing enzymes
or proteins, or turning genes on or off.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 11-14
Growth factor
Reception
Receptor
Phosphorylatio
n
cascade
Transduction
CYTOPLASM
Inactive
transcription
factor
Active
transcription
factor
P
Response
DNA
Gene
NUCLEUS
mRNA
Fig. 11-15
Reception
Binding of epinephrine to G protein-coupled 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)
Apoptosis
• Apoptosis – A response that is a programmed or
controlled cell suicide
• A cell is chopped and packaged into vesicles that are
digested to prevent enzymes from leaking out and
damaging other cells
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Triggering Apoptosis
• Apoptosis can be triggered by:
– An extracellular death-signaling ligand
– DNA damage in the nucleus
– Protein misfolding in the endoplasmic reticulum
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
You should now be able to:
1. Describe the nature of a ligand-receptor
interaction and state how such interactions
initiate a signal-transduction system
2. Compare and contrast G protein-coupled
receptors, tyrosine kinase receptors, and
ligand-gated ion channels
3. List two advantages of a multistep pathway in
the transduction stage of cell signaling
4. Explain how an original signal molecule can
produce a cellular response when it may not
even enter the target cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
5. Define the term second messenger; briefly
describe the role of these molecules in
signaling pathways
6. Explain why different types of cells may
respond differently to the same signal
molecule
7. Describe the role of apoptosis in normal
development and degenerative disease in
vertebrates
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings