Problem 4
Question
Consider this pathway: epinephrine \(\rightarrow\) G protein-coupled receptor \(\rightarrow G\) protein \(\rightarrow\) adenylyl cyclase \(\rightarrow\) cAMP. Identify the second messenger. $$ \begin{array}{ll}{\text { (A) } \operatorname{cAMP}} & {\text { (C) GTP }} \\\ {\text { (B) Grotein }} & {\text { (D) adenylyl cyclase }}\end{array} $$
Step-by-Step Solution
Verified Answer
The second messenger in the pathway is cAMP.
1Step 1 - Understand the Pathway
The pathway provided shows the sequence of molecular interactions starting from epinephrine leading to the production of cAMP.
2Step 2 - Identify the Role of cAMP
In cellular pathways, cAMP often acts as a second messenger. It relays the signal from the receptor to other molecular targets within the cell.
3Step 3 - Verify Second Messenger
By examining the pathway: epinephrine (the first messenger) binds to the receptor, which activates G protein, leading to the activation of adenylyl cyclase, which converts ATP into cAMP. cAMP then propagates the signal within the cell.
4Step 4 - Choose the Correct Option
From the provided choices, (A) cAMP is the correct answer as it matches the role of the second messenger in the pathway.
Key Concepts
G protein-coupled receptoradenylyl cyclasecAMP
G protein-coupled receptor
G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that respond to various external signals.
When a molecule like epinephrine binds to a GPCR, it causes the receptor to change shape.
This shape change allows the receptor to interact with a nearby G protein, specifically activating it.
The activation of the G protein involves swapping GDP for GTP. This step is essential for further signaling inside the cell.
The activated G protein can then affect other molecules inside the cell. In our pathway, it activates adenylyl cyclase.
Understanding how GPCRs work is crucial because they are involved in many physiological processes, from sensory perception to immune responses.
When a molecule like epinephrine binds to a GPCR, it causes the receptor to change shape.
This shape change allows the receptor to interact with a nearby G protein, specifically activating it.
The activation of the G protein involves swapping GDP for GTP. This step is essential for further signaling inside the cell.
The activated G protein can then affect other molecules inside the cell. In our pathway, it activates adenylyl cyclase.
Understanding how GPCRs work is crucial because they are involved in many physiological processes, from sensory perception to immune responses.
adenylyl cyclase
Adenylyl cyclase is an enzyme located on the inner side of the cell membrane.
Its main function is to convert ATP, a molecule that carries energy, into cyclic AMP (cAMP), which acts as a second messenger.
When a GPCR activates a G protein, the G protein can then activate adenylyl cyclase.
Once activated, adenylyl cyclase catalyzes the conversion of ATP to cAMP.
This conversion process is critical because cAMP plays an essential role in propagating the signal within the cell.
This continuation of the signal can influence various cellular processes, including gene expression, enzyme activity, and cell metabolism.
So, adenylyl cyclase acts as a bridge between the initial signal received by the GPCR and the secondary signaling processes inside the cell.
Its main function is to convert ATP, a molecule that carries energy, into cyclic AMP (cAMP), which acts as a second messenger.
When a GPCR activates a G protein, the G protein can then activate adenylyl cyclase.
Once activated, adenylyl cyclase catalyzes the conversion of ATP to cAMP.
This conversion process is critical because cAMP plays an essential role in propagating the signal within the cell.
This continuation of the signal can influence various cellular processes, including gene expression, enzyme activity, and cell metabolism.
So, adenylyl cyclase acts as a bridge between the initial signal received by the GPCR and the secondary signaling processes inside the cell.
cAMP
Cyclic AMP (cAMP) stands for cyclic adenosine monophosphate and is a key second messenger in many biological pathways.
Its role is to relay signals inside the cell, amplifying the original signal received by the cell receptor.
In the pathway shown, once adenylyl cyclase is activated, it converts ATP into cAMP.
The produced cAMP can then activate other proteins within the cell, such as protein kinase A (PKA).
Activation of PKA can lead to the phosphorylation of various target proteins, altering their activity and thus propagating the initial signal started by epinephrine.
This entire cascade ensures that the cell responds appropriately to external stimuli.
In summary, cAMP serves as a crucial intermediary in cellular signaling, translating extracellular messages into appropriate actions within the cell.
Its role is to relay signals inside the cell, amplifying the original signal received by the cell receptor.
In the pathway shown, once adenylyl cyclase is activated, it converts ATP into cAMP.
The produced cAMP can then activate other proteins within the cell, such as protein kinase A (PKA).
Activation of PKA can lead to the phosphorylation of various target proteins, altering their activity and thus propagating the initial signal started by epinephrine.
This entire cascade ensures that the cell responds appropriately to external stimuli.
In summary, cAMP serves as a crucial intermediary in cellular signaling, translating extracellular messages into appropriate actions within the cell.
Other exercises in this chapter
Problem 3
Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because (A) only target cells retain the a
View solution Problem 5
Apoptosis involves all but which of the following? (A) fragmentation of the DNA (B) cell-signaling pathways (C) lysis of the cell (D) digestion of cellular cont
View solution Problem 6
Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? (A) Enzymatic activity was proportional
View solution Problem 7
Protein phosphorylation is commonly involved with all of the following except (A) activation of receptor tyrosine kinases. (B) activation of protein kinase mole
View solution