cAMP Q

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cAMP Q

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Tiff
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04/07/08 - 01:14 PM

In the fasting state, which of the folowing statements about cAMP best describes its mechanism of action?

A. It activates adenylate cyclase when complexed with the alpha-subunit of Gs protein

B. It activates protein kinase A to become a regulator of enzymes by phosphorylation.

C. It binds calcium to activate several cellular enzymes.

D. It binds to receptors on the endoplasmic reticulum, causing calcium to be released into the cytoplasm.

E. It increases the activitiy of membrane-bound protein kinase C.

new_n_lost
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04/07/08 - 01:34 PM

B. It activates protein kinase A to become a regulator of enzymes by phosphorylation.
A very HY question for the exam.

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sigh
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04/07/08 - 01:48 PM

Can somebody explain why it is not A? I know that cAMP will activate adenylate cyclase thr. G-protein and then protein kinase A. does it have something to do with alpha subunit? What is alpha-subunit?

new_n_lost
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04/07/08 - 02:27 PM

I think it goes something like this.

A stimuli attaches to G protein then it activates adenylyl cyclase and then ATP --> AMP --> Protein Kinase A.

This is how i remember it but i will recheck it just to be sure.

Second messengers are very very HY everyone does get a question like that.

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new_n_lost
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04/07/08 - 02:29 PM

The activation of adenylyl cyclase is not dependent on cAMP but on G proteins however it can be mandated by cellular energy levels.

As again Moi 2 cents.

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jean robert
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04/07/08 - 05:46 PM

B

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sigh
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04/08/08 - 06:44 AM

Hi new_n_lost! Check me ...
Gs---->adenylate cyclase A---->c AMP---->protein kinase A----->phosporylation of E-s
If above chain looks ok then why A is not correct?

macintosh
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04/08/08 - 08:47 AM

Isn't this the GLUCAGON World?

Glucagon binds to its receptor (G protein) which activates adenylate cyclase. Adenylate cyclase in turn manufactures cAMP activating protein kinase A, causing phosphorylation of enzymes. Glycogen phosphorylase thus formed breaks down glycogen.

By the way sigh your explanation is correct, and this is why A is incorrect.

sigh
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04/08/08 - 10:06 AM

thanks macintosh

new_n_lost
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04/08/08 - 12:51 PM

#10

@ Sigh A is incorrect becos it says IT ACTIVATES adenylyl cyclase. which it doesnt. G proteins whenever stimulated get adenylyl cyclase activated which leads to ATP to AMP and thus leading to the cascade downwards.

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sigh
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04/08/08 - 01:21 PM

#11

thanks new and lost

Tiff
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04/08/08 - 01:25 PM

#12

new_n_lost wrote:
@ Sigh A is incorrect becos it says IT ACTIVATES adenylyl cyclase. which it doesnt. G proteins whenever stimulated get adenylyl cyclase activated which leads to ATP to AMP and thus leading to the cascade downwards.

B is correct. NNL explains it well why A is incorrect.

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