Biochemistry : Signal Transduction Pathways
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Example Question #51 : Signal Transduction Pathways
How do diacylglycerol (DAG) and IP3 (inositol triphosphate) act as second messengers?
I. Phospholipase catalyses the formation of DAG and IP3 from PIP2 (phosphatidylinositol-4,5-bisphosphate)
II. IP3 increases intracellular calcium ion levels
III. DAG stimulates protein kinase C
IV. Protein kinase C activates protein kinases known as the MAP kinases
II and III
I, II, III, and IV
II, III, and IV
III and IV
I and II
I, II, III, and IV
Phospholipase C catalyses the formation of DAG (diacylglycerol) and IP3 (inositol triphosphate) from PIP2 (phosphatidylinositol-4,5-bisphosphate). IP3 promotes the influx of calcium ions into the cytoplasm while DAG stimulates protein kinase C.
Example Question #52 : Signal Transduction Pathways
How does nitric oxide act as a second messenger?
I. Nitric oxide activates guanylate cyclase.
II. Nitric oxide promotes formation of the intracellular messenger cyclic guanosine monophosphate (cGMP).
III. An increase of cGMP due to nitric oxide causes vasodilation.
IV. Nitric oxide promotes formation of cyclic adenosine monophosphate (cAMP)
I and IV
I, II, and III
II and III
II, III, and IV
I and II
I, II, and III
Nitric oxide is a gas second messenger.It is also a neurotransmitter in the brain. Nitric oxide is produced by 3 enzymes: endothelial, induced, and neuronal nitric oxide synthases. Nitric oxide synthases require a calcium ions for the enzyme activity. Nitric oxide does act thru the cyclic guanosine monophosphate activation pathway.
Example Question #20 : Second Messengers
Which of the following is not associated with signal transduction pathways?
Activation of protein kinase A
Breakdown of phosphatidylinositol bisphosphate
Synthesis of beta-hydroxybutyrate
Activation of phosphodiesterases
Dissociation of G protein subunits
Synthesis of beta-hydroxybutyrate
In this question, we're asked to identify a statement that is not connected with intracellular signal transduction pathways (STP). To do so, we'll need to look at each answer choice individually.
Upon binding of a ligand to a G protein-coupled receptor (GPCR), the conformational change of this receptor is transmitted to a G-protein that is on the inner leaflet of the plasma membrane. This causes the individual sub-units of the G-protein to dissociate from each other, which then goes on to activate other components of the signal transduction pathway.
Activation of GPCR can also result in a signal transduction pathway in which a particular intracellular enzyme is activated. This enzyme is responsible for cleaving a specific fatty acid off of certain phospholipids from the plasma membrane. The fatty acid cleaved off is called phosphatidylinositol bisphosphate, which acts as a second messenger in STP's.
Another consequence of the activation of certain GPCR's is the activation of an enzyme called protein kinase A (PKA). This enzyme then goes on to phosphorylate other kinase enzymes. The end result is amplification of the entire signal.
One of the common second messengers in STP's is cyclic AMP (cAMP) and cyclic GMP (cGMP). One of the mechanisms in place to turn STP's off is to degrade these cyclic nucleotides. The class of enzymes responsible for this is called phosphodiesterases.
Beta-hydroxybutyrate is a ketone body that forms when excess acetyl-CoA is present. This molecule is not involved in signal transduction pathways.
Example Question #21 : Second Messengers
In a G protein-coupled receptor, the activation of an inhibitory G protein will lead to which of the following?
The decrease in cAMP
Adenyl cyclase hydrolysis of ATP
An inactivated alpha subunit of the G protein
Downstream activation of PKA
The activation of adenylyl cyclase
The decrease in cAMP
With an inhibitory G protein, the binding of a ligand and stimulation of the receptor will activate the alpha subunit of the G protein, however since it is an inhibitory G protein, it will not go on to activate adenyl cyclase. With no activation of Adenyl cyclase it will lead to decrease cAMP and other secondary messengers.
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