Download - AP Biology Cell communication
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Transduction of a Signal is Usually a Multi-Step Pathway
In this case, there are two advantages:1. A small number of extracellular signal
molecules can produce widespread cellular response. 2. Provides more opportunities for
coordination & regulation than in simpler systemsAnalogy:
vs.
On/off switchis like a singlestep pathway Dimmer=
multi-step
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Cell Communication –Signal Transduction
Ch. 5 section
5.6
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Signal Transduction Pathways
•The binding of a specific signal to its receptor triggers a chain reaction that leads to a response.•Relay molecules are the proteins that “carry the message” down a reaction chain
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Ligand doesn’t enter cell
Remember: the Remember: the signal molecule signal molecule itselfitself doesn doesn’’t t physically physically get passed down get passed down the pathway.the pathway.
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2 common transduction events
1. Phosphorylation= the transfer of a phosphate group from ATP to a protein – thereby activating the protein
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Protein kinase is the enzyme that transfers phosphate groups from ATP to proteins
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Protein kinases are numerous and help regulate cell reproduction. Therefore, abnormal kinase activity can contribute to cancer.
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In addition to protein kinases, protein phosphatases also play a role in the cascade
Protein phosphatases are enzymes that dedephosphorylate proteins
phosphatases turn off signal transduction
Phosphatases also make kinases available for re-use
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QUICK THINKQUICK THINKExplain how a phosphorylation cascade gets turned off
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2 common transduction events
2. Second messengers: small, nonprotein, water-soluble molecules or ions; the signal molecule being the “first messenger.”
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2 common second messengers Cyclic AMP (or cAMP)
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Example ofcAMP as a Second Messenger
The binding of epinephrine,the first messenger, activates adenylyl cyclase, which then catalyzes the synthesis of cAMP in a liver cell. The response isthe breakdown of glycogen within the cell.
Boosts your energy!
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cAMP Malfunctioning
Vibrio cholerae produces a toxin that modifies the G protein, which is now stuck in the on position.
G protein is unable to hydrolyze GTP to GDP
Now high concentrations of cAMP cause intestinal cells to secrete water & salts- may lead to death w/in hours
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cAMP’s role in cells1. Caffeine artificially boosts your
energy by blocking the breakdown of cAMP, keeping you alert even without epinephrine
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2 common second messengers•Ca2+ the ER released stored calcium •cause cellular responses including muscle
contraction & cell division.