Chemical Signaling Between Cells

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Chemical Signaling Between Cells

• Three general categories of chemical signaling
• Cytoplasmic connections between cells
• Cell-to-cell contact-mediated signaling
• Free diffusion between cells
• Distant cells (hormones)
• Adjacent cells (within interstitial space)
• All of latter involves the physical movement of
  Ligands
• That is, Ligand Reception by a Protein
• Note that Reception means Molecule-to-Molecule
  Contact

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Chemical Signaling Between Cells
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Long-Distance Diffusion
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Local Diffusion
e.g., Histamine released from damaged cells in
inflammation
e.g., Interferon release by viral-infected cells
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Local Diffusion
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Signal-Transduction Emphasis
This chapters emphasis is on signals that are
released from one cell and allowed to freely
diffuse to a second (or more) recipient
cell(s) These communications are deliberately
initiated, received, and interpreted in order to
increase the physiological coordination of the
cells in multicellular organisms We will consider
in particular those events that follow the
reception of chemical signals We will not dwell
on the purpose of the signal We also will not
dwell on why and how a given cell released a
given signal
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Three Stages of Signal Transduction

• Reception of extracellular signal by cell
• Transduction of signal from outside of cell to
  inside of celloften multi-stepped
• Note not necessarily transduction of ligand
• Cellular Response
• Response is inititiated and/or occurs
  entirely within receiving cell

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Three Stages of Signal Transduction
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Three Stages
2a. Transduction
2b. Transduction
2c. Transduction
2d. Transduction
Responses usually involve increasing or
decreasing some Proteins Function
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Three Stages
1. Reception
2a. Transduction
2b. Transduction
3. Response
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Various Responses
Note that more than one response can result from
the reception of a single ligand
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Various Responses
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Ligands
e.g., nitric oxide
e.g., steroid hormones
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Intracellular Reception
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Extracellular Reception
e.g., insulin
e.g., epinephrine
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Examples of Surface Receptors
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G Protein-Linked Receptors
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G Protein-Linked Receptors
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G Protein-Linked Receptors
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G Protein-Linked Receptors
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G Protein-Linked Receptors
the more ligand binding, the greater the cellular
response
note how activation is reversible
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G Protein-Linked Receptors
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G Protein-Linked Receptors
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G Protein-Linked Receptors
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G Protein-Linked Receptors
note how activation is reversible
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G Protein-Linked Receptors
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Protein Kinase Phosphatase
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Tyrosine Kinase Receptors

• Note steps involved
• Ligand Reception
• Receptor Dimerization
• Catalysis (Phosphorylization)
• Subsequent Protein Activation
• Further Transduction
• Response

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Tyrosine Kinase Receptors
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Ion-Channel Receptors
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Signal Amplification (Cascade)
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Phosphorylation Cascade

• This reversibility contributes to the dynamic
  nature of cells
• A protein that is activated by a Protein Kinase
  in turn is inactivated by a Protein Phosphatase
• This means that the effect of signals cant last
  forever
• For the cellular response to continue, more
  signal must be received

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Phosphorylation Cascade
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Epinephrine ? Glycogen Breakdown
100 molecules 102 molecules 104 molecules 104
molecules 105 molecules 106 molecules
108 mol Glu-1-Phosphate
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Second Messengers
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Cyclic AMP (cAMP) 2nd Messenger
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Inositol Triphosphate 2nd Messenger
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Transduction Pathway Cross-Talk
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Specificity of Cell Signaling

• Note how same ligand gives rise to different
  responses
• Cells differ in terms of their proteins
• Different proteins respond differently to the
  same environental signals
• (note, though, same receptors, different relay)
• Different cells behave differently because some,
  but not all proteins can differ between cell types

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Link to Next Presentation
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Acknowledgements
biology.ucf.edu/courses/bsc2010/08-2010C-02.PPT ww
w.aw.com/bc/ppt/marieb_ap/chap03c.ppt http//zeus.
uwindsor.ca/courses/biology/zielinski/204/comm1.pp
t http//vaccine.chonbuk.ac.kr/images/cell/Chapter
201520Cell.ppt http//faculty.uca.edu/jmurray/B
IOL1440/lec/lec15.ppt \http//www.rpi.edu/dept/bcb
p/molbiochem/MBWeb/mb1/part2/7-signal.ppt http//w
ww.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/9-
glycogen.ppt http//homepage.smc.edu/chen_thomas/B
io21/Chpt201120Cell20Comm.ppt
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G Protein-Linked Receptors
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G Protein-Linked Receptors