Chapter 11: Cell Communication

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Chapter 11Cell Communication
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Important Point
If you are having trouble understanding lecture
material Try reading your text before
attending lectures. And take the time to read it
well!
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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 a chemical signal
• We will not dwell on the purpose of the signal
• We also will not dwell on why and how a given
  cell releases a given signal

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Signaling with Direct Contact
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Local Signaling w/o Direct Contact
e.g., interferon release by viral-infected cells
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Long-Distance Signaling
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Long-Distance Diffusion
Note how specificity is determined by
presence/absence of receptor protein
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Signalling, Free-Living Cells
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Cell-Cell Chemical Signaling

• 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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Ligands
e.g., nitric oxide
e.g., steroid hormones
Nothing to memorize on this page
e.g., insulin
e.g., epinephrine
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Signal Transduction
Often turning on or off enzyme activity
In this case the receptor protein is a membrane
protein
Ligand
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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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Intracellular Receptor
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Rapidity of Response
Slower response if requiring protein synthesis
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G-Protein-Linked Receptor
G proteins bind GTP
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G-Protein-Linked Receptor
The more ligand binding, the greater the cellular
response
Note lability of all signals
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Protein Kinase Phosphatase
Therefore, responses tend to continue (or expand)
only so long as signaling continues
This reversibility contributes to the dynamic
nature of cells
Like signal lability, reversibility of
phosphorylation makes signaling reversible
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Tyrosine Kinase Receptor
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Receptor Tyrosine Kinase

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

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Ion-Channel Receptor
Reversibility is assured by pumping ions back out
again (using separate protein)
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Phosphorylation Cascade
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Cyclic AMP (cAMP)
Note reversibility
Second Messenger
Second messengers are not proteins
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2nd Messenger, S.T.P.
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Ca2-mediated Signal Amp.
Releasing Ca2 is a means of greatly amplifying
signal
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Signal Amplification (Cascade)
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Signal Amplification (Cascade)
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Signal Amplification (Cascade)
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Signal-Transduction Cascade
Seek to understand the concept, rather than
memorize the specific protein
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Nuclear 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

• Same ligand gives rise to different responses
• (here same receptor, different relay)
• Cells differ in terms of their proteins
• Different proteins respond differently to the
  same environmental signals

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The End