Question

You may choose more than one answer. Which of the following is a mechanism of signal amplification in the cAMP-PKA pathway?

One signal molecule, epinephrine, activates lots of G-proteins.

When activated, adenylyl cyclase synthesizes many cAMP molecules.

cAMP-activated protein kinase A (PKA) can activate a number of target proteins by phosphorylation.

Proteins phosphorylated by PKA can further activate other proteins that make other products

Answer 1

Your answers are

1:When activated, adenylyl cyclase synthesizes many cAMP molecules.

2: cAMP-activated protein kinase A (PKA) can activate a number of target proteins by phosphorylation

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EXPLANATION

As long as epinephrine remains bound to a receptor, the receptor can activate a succession of G proteins.

In addition, each adenylyl cyclase enzyme can convert numerous ATPs into cyclic AMP molecules.

Other activated enzymes in the pathway can also continually catalyze reactions.

The G protein, in contrast, activates just a single adenylyl cyclase enzyme and must remain attached to it in order for adenylyl cyclase to remain activated.

The steps describing the phenomenon are -

1:epinephrine signaling occurs when the hormone binds to an epinephrine receptor on the cell surface. (activates only a type of G protein)

2:The hormone triggers the receptor to change shape, converting the receptor to its active form.

3: activated receptor triggers a cascade of events within the cell, beginning with the activation of a G protein.

4: The G protein binds to the activated receptor, releases GDP, and takes up a molecule of GTP.

5: After taking up GTP, the G protein is released from the receptor and splits into two parts. One of the parts is activated and continues the signaling cascade.

6: Soon, the hormone also leaves the receptor, and the receptor reverts to its inactive form.

7: The G protein then inturn activates an enzyme called adenylyl cyclase. When activated, adenylyl cyclase converts a large number of ATP molecules into signaling molecules, called cyclic AMP or cAMP.

8: After that, in response to a stimulus the G protein soon inactivates itself by cleaving GTP, and the subunits reassociate. With the G protein no longer attached, the adenylyl cyclase turns off and can no longer convert ATP into cAMP.

9: Following that, the cAMP molecules produced by adenylyl cyclase continue the signaling cascade by binding to a type of enzyme called protein kinase A. This binding triggers protein kinase A to separate into subunits, which are enzymatically active.

10: These activated protein kinases A subunits perform certain chemical reactions in which they add phosphate groups to another type of enzyme, called phosphorylase kinase.

11: The addition of the phosphate groups activates phosphorylase kinase.

12: This Phosphorylase kinase, in turn, phosphorylates another enzyme, called glycogen phosphorylase. When phosphorylated, this enzyme also becomes activated.