ap biology cell communication
TRANSCRIPT
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
Cell Communication –Signal Transduction
Ch. 5 section
5.6
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
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.
2 common transduction events
1. Phosphorylation= the transfer of a phosphate group from ATP to a protein – thereby activating the protein
Protein kinase is the enzyme that transfers phosphate groups from ATP to proteins
Protein kinases are numerous and help regulate cell reproduction. Therefore, abnormal kinase activity can contribute to cancer.
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
QUICK THINKQUICK THINKExplain how a phosphorylation cascade gets turned off
2 common transduction events
2. Second messengers: small, nonprotein, water-soluble molecules or ions; the signal molecule being the “first messenger.”
2 common second messengers Cyclic AMP (or cAMP)
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!
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
cAMP’s role in cells1. Caffeine artificially boosts your
energy by blocking the breakdown of cAMP, keeping you alert even without epinephrine
2 common second messengers•Ca2+ the ER released stored calcium •cause cellular responses including muscle
contraction & cell division.