Signal Transduction Pathways - DOC

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					Signal Transduction Pathways
Odorant neuron Skeletal muscle cell

Signal molecule (source)

odorant molecule (from air in the nasal passageway) odorant G-protein-linked receptor 1. G-protein (especially α-subunit)

acetylcholine (from motor neuron) acetylcholine-gated Na+ channel 1. voltage-gated Na+ channels (action potential-producing) 2. voltage sensor proteins of T tubules

Receptor

Transduction pathway members (proteins)

2. adenylyl cyclase 3. cAMP-gated Ca2+, Na+ channel 3. Ca2+ release channels 4. Ca -gated Cl channels 4. troponin cAMP (1st) and Ca2+ (2nd) Na+ (?) and especially Ca2+
2+ -

Second messenger(s) in transduction pathway

When the odorant molecule is bound to its receptor, many G-proteins can be activated. How amplification is achieved in transduction pathway (a few sentences) Adenylyl cyclase is an enzyme and can convert many ATP molecules to cAMP. The cAMP-gated Ca2+,Na+ channel is a channel and many Ca2+ and Na+ ions rush in when it’s open. The Ca2+-gated Cl- channel is a channel and many Cl- ions rush out when it’s open.

Both voltage-gated channels are channels and many Na+ or Ca2+ ions rush into the cytosol when they are open.

Response (a few sentences)

The plasma membrane depolarizes (due to the rushing in of Na+ cations through the cAMP-gated Ca2+,Na+ channels and the rushing out of Cl- anions through the Ca2+-gated Cl- channels) past the threshold level and an action potential travels down the axon to the mitral cell.

When troponin binds Ca2+ cations, it moves tropomyosin so it no longer blocks the myosin binding sites on the actin thin filaments, so the thick filaments can move the thin filaments toward the center of the sarcomere. The muscle contracts!

Signal Transduction Pathways
α1-type receptor (liver cell) β-type receptor (liver cell)

Signal molecule (source)

epinephrine (from adrenal medulla) α1-type epinephrine G-protein-linked receptor 1. G-protein (especially α-subunit)

epinephrine (from adrenal medulla) β-type epinephrine G-protein-linked receptor 1. G-protein (especially α-subunit) 2. adenylyl cyclase 3. cAMP-dependent protein kinase A 4. phosphorylase kinase 5. glycogen phosphorylase

Receptor

Transduction pathway members (proteins)

2. phospholipase C 3. IP3-gated Ca2+ channels on the endoplasmic reticulum (IP3 is inositol triphosphate) and DAG-gated Ca2+ channels in the plasma membrane (DAG is diacylglyceride) IP3 and Ca2+ (DAG isn’t usually considered a 2nd messenger since it isn’t water soluble) When epinephrine is bound to its α1-type receptors many G-proteins are activated.

Second messenger(s) in transduction pathway

cAMP

When epinephrine is bound to its β-type receptors many G-proteins are activated. Adenylyl cyclase is an enzyme and so can convert many molecules of ATP to cAMP. Each enzyme in the phosphorylation cascade (3 - 5 above) amplifies the signal because enzymes can convert many molecules of substrate to product.

How amplification is achieved in transduction pathway (a few sentences)

Phospholipase C is an enzyme and so can convert many molecules of PIP2 to IP3 and DAG. The IP3-gated Ca2+ channels and the DAGgated Ca2+ channels are channels and so many Ca2+ cations can enter while they’re open.

Main response is the phosphorolysis of glycogen to glucose and its release into the blood. Response (a few sentences) The enzyme that activates glycogen phosphorylase needs Ca2+ to be fully active and this pathway provides the Ca2+.

Main response is the phosphorolysis of glycogen to glucose and its release into the blood. Glycogen phosphorylase must have a phosphoryl group added to be active and this pathway provides the phosphoryl group.