• It applies to ALL the membrane receptors EXCEPT the ligandgated ion channel, because all that does is open
up and let stuff in, which in itself IS the passingon of the signal
o Explain the concept of signal amplification and how cells do it.
• Signal amplification some signal is made larger, or amplified
This happens in the cell when the reception of a single first messenger molecule causes the activation of an
amplifier enzyme which will create SEVERAL more molecules which in turn go and do stuff thus it is NOT a
1:1 ratio between each step…instead everything has been amplified
o State the basic pattern of a biological signal transduction pathway.
See Figure 6.8, pg. 177
• An extracellular SIGNAL MOLECULE binds to and activates a protein/glycoprotein MEMBRANE RECEPTOR
• Then the receptor turns on its associated proteins, which can do a number of things:
Activate PROTEIN KINASES: these guys are enzymes which phosphorylate a protein, which either
activates or inactivates it
Activate AMPLIFIER ENZYMES: these guys create SECOND MESSENGERS which do stuff…
• The second messengers (if they are created) can also do a VARIETY of things:
Alter the open state of ION CHANNELS: as you may expect, this will affect the cell's MEMBRANE
Increase INTRACELLULAR CALCIUM: either calcium will get let in from the OUTSIDE or we will
see its release from INTRACELLULAR STORES…either way calcium can bind to proteins and
change their function
CHANGE ENZYME ACTIVITY: especially of protein kinases (discussed earlier) or protein
phosphatases (REMOVE a phosphate group from a protein)
• And then the ultimate result: the proteins modified by calcium binding and (de)phosphorylation control one or
more of the following:
Motor proteins for muscle contraction/cytoskeletal movement
Regulate gene activity and protein synthesis
Membrane transport and receptor proteins
o Explain the concept of a signal cascade, and how it is applicable here.
The idea is that when a first messenger hits the cell, often there are many steps before the ultimate response.
Each step involves the conversion of something from an inactive form to an active form, which then catalyzes
the conversion of another thing from inactive to active, and so on…hence our CASCADE
• Receptorenzymes have protein kinase or guanylyl cyclase activity
o Don't cheat! What are the enzymes of receptorenzymes? What happens as a result?
• Either we have protein kinases as the enzyme (for example TYROSINE KINASE, in which case a tyrosine
residue of a protein will get phosphorylated)
Or we can have GUANYLYL CYCLASE as the enzyme, which will get activated and convert GTP to cyclic GMP
• Most signal transduction uses G proteins
o OK so explain how the whole Gprotein coupled receptor system works in general.
• Well first we have the RECEPTOR itself, which is generally a MEMBRANESPANNING PROTEIN that crosses
the phospholipid bilayer of the membrane SEVEN times, forward and back
• And then the receptor is linked to a 3part tranducer molecule which is our G PROTEIN. This thing is called a
G protein because they are bound to guanosine nucleotides either GDP or GTP
When it is a GDP, the protein is inactivated but when it gets exchanged for a GTP we get
activation, and the G protein takes further action either by:
• Opening an ion channel in the membrane
• Or altering enzyme activity the most common enzyme is ADENYLYL CYCLASE or
Adenylyl cyclasecAMP is the signal transduction system for many lipophobic hormones
o Explain how the G proteincoupled adenylyl cyclasecAMP system works.
• See Figure 6.11, pg. 180
• G proteinlinked receptors also use lipidderived second messengers
o Just quickly, what is the result of the Gprotein coupled PLC system?