Actions of the Second Messenger and Protein Kinase A

by Kevin Ahern, PhD

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    So the cyclic AMP as a second messenger has to interact with other molecules to cause that signal to be transmitted because if it doesn’t, then there won’t be a signal. Well it turns out that cyclic AMP goes and interacts with a protein known as protein kinase A. Now protein kinase A as its name suggests is a protein of course, and it’s also an enzyme. But in the normal state, protein kinase A is in the inactive form, meaning it’s not catalyzing any reaction. And that’s because the protein kinase A has its catalytic part of itself having been covered up. The covering up of the catalytic part prevents the catalytic part from catalyzing a reaction. So we can see that in this depiction here. We see that protein kinase A has four subunits associated with it. Two units that are in red with an R in them, indicating that they’re regulatory subunits. And these subunits are covering up that catalytic site. The two C subunits in blue are where the catalytic site is located. Well here comes our four molecules of cyclic AMP that has been produced by the adenylate cyclase in the previous reaction. What happens is, these four cyclic AMPs convert the inactive form of protein kinase A into the active form. And the way they do that is by binding to the regulatory subunits. Now as we’ve seen time and again in these lectures, binding of a molecule to a protein, slightly changes that protein’s shape, in this case the regulatory subunits. And the regulatory subunits with their change in shape can no longer bind to the catalytic subunits. Consequently the catalytic subunits are released and now their catalytic sites are open and exposed to all the molecules in the cell. They can begin...

    About the Lecture

    The lecture Actions of the Second Messenger and Protein Kinase A by Kevin Ahern, PhD is from the course Hormones and Signal Transduction. It contains the following chapters:

    • Actions of the Second Messenger
    • Protein Kinase A

    Included Quiz Questions

    1. None of the answers are true.
    2. Phosphorylation activates all of the enzymes.
    3. Phosphorylation inactivates all of the enzymes.
    4. Glycogen synthesis and breakdown occur simultaneously.
    5. All of the answers are true.
    1. All of the answers are true.
    2. The binding of epinephrine stops glycogen synthesis.
    3. When glycogen synthase is phosphorylated, it is inactive
    4. The production of cAMP activates protein kinase A.
    5. None of the answers are true.

    Author of lecture Actions of the Second Messenger and Protein Kinase A

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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