1. Reception, Transduction, Response
Cell Communication
Reception, Transduction, Response

2. 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. 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

4. Long Distance Signaling
Hormones – chemical messengers that travel long distance.
Ex. Through blood vessels

5. 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

6. 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

7. 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

8. 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.

9. 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

10. 1 Signaling molecule (ligand) Gate closed Ions Plasma membrane
Fig. 11-7d 1
Signaling
molecule
(ligand)
Gate
closed
Ions
Plasma
membrane
Ligand-gated
ion channel receptor 2
Gate open
Cellular
response
Figure 11.7 Membrane receptors—ion channel receptors 3
Gate closed

11. 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

12. 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

13. Phosphorylation/Dephosphorylation
Phosphorylation – add phosphates (turns protein on)
Dedphosphorylation – removes phosphates (turns proteins off)
Protein kinases – does phosphorylation
Protein phosphatases- does dephosphorylation
Phosphorylation Cascade

15. 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

16. EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein
Fig
EXTRA-
CELLULAR
FLUID
Signaling molecule
(first messenger)
G protein
DAG
GTP
G protein-coupled
receptor
PIP2
Phospholipase C
IP3
(second messenger)
IP3-gated
calcium channel
Figure Calcium and IP3 in signaling pathways
Endoplasmic
reticulum (ER)
Ca2+
Ca2+
(second
messenger)
CYTOSOL

17. Response
Cell usually respond by synthesizing enzymes or proteins, or turning genes on or off.
Figure Nuclear responses to a signal: the activation of a specific gene by a growth factor
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

18. Growth factor Reception Receptor Phosphorylation cascade Transduction
Fig
Growth factor
Reception
Receptor
Phosphorylation
cascade
Transduction
CYTOPLASM
Inactive
transcription
factor
Active
transcription
factor
Figure Nuclear responses to a signal: the activation of a specific gene by a growth factor
Response P
DNA
Gene
NUCLEUS
mRNA

19. Glucose-1-phosphate (108 molecules)
Fig
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)
Figure Cytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrine
Inactive phosphorylase kinase
Active phosphorylase kinase (105)
Inactive glycogen phosphorylase
Active glycogen phosphorylase (106)
Response
Glycogen
Glucose-1-phosphate
(108 molecules)

20. 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

21. 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

22. You should now be able to:
Describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction system
Compare and contrast G protein-coupled receptors, tyrosine kinase receptors, and ligand-gated ion channels
List two advantages of a multistep pathway in the transduction stage of cell signaling
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

23. Define the term second messenger; briefly describe the role of these molecules in signaling pathways
Explain why different types of cells may respond differently to the same signal molecule
Describe the role of apoptosis in normal development and degenerative disease in vertebrates
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings