Cell Communication and Cell Signaling Student Learning Guide

1. Introducing cyclic AMP, the Second Messenger

Let’s review what we’ve learned so far.

Firstly, we’ve learned that there are three phases involved in cell communication:

  • I. Reception
  • II. Signal transduction
  • III. Cellular response.

The preceding section and quiz examined the events connected with reception. We’ve seen how a polar hormone like epinephrine (“1,” in the diagram to your right) binds with a G-protein coupled receptor (“2”). Binding causes changes in the receptor, which in turn causes changes in a nearby G protein (“3”), allowing it to become activated by binding with GTP (“4”). This activated G-protein can now activate a nearby enzyme (“5”).

The events that follow (which includes “5” through “9”) are now going to be our focus. The movement of activity from the membrane to the cytoplasm involves transduction of the signal: changing the signal into a different form that induces cytoplasmic changes.

In our ongoing story of liver cells converting glycogen to glucose, the enzyme  (shown at “5”) would be adenylyl cyclase. Adenylyl cyclase is widely shared among eukaryotes, and enzymes with similar functions are found among prokaryotes as well. The enzyme’s function is to convert ATP (represented by “6” above) into cyclic AMP (“7” above, and also at right).

Cyclic AMP (cAMP)

Cyclic AMP (adenosine monophosphate) has one phosphate group. Because of the way the the phosphate group is connected to the ribose sugar in the molecule (note the two covalent bonds), it’s called cyclic AMP (which is different in form and function from regular (non-cyclic) AMP). Cyclic AMP acts as a second messenger. Unlike the first messenger (epinephrine), cyclic AMP (or cAMP) goes into the cytoplasm, causing a series of changes that ultimately bring about a cellular response.

Immediately below, you can see another representation that shows the action of adenylyl cyclase (represented by number “2”). ATP (at “1”) acts as adenyl cyclase’s substrate, and two products result: two attached phosphate groups (at “3”) and cyclic AMP (at “4”)

After cAMP is created by adenylyl cyclase (“5” below) cAMP’s role is to activate other proteins (shown at “8”), which then bring about the desired cellular response (“9”). What that means, in the context of our story in the liver, is activating “dormant” enzymes that break down the polysaccharide glycogen into glucose, enabling glucose to be released into the bloodstream to power the flight or flight response.

What this diagram doesn’t communicate, however, is that having second messengers like cAMP relay messages to other proteins allows for amplification of the original signal. Imagine a more complicated diagram in which adenylyl cyclase (“5”) is going to catalyze the production of many cAMPs (“6”), each of which will in turn activate many proteins (“8”), so that by the end of the process, millions of enzymes will have been activated. In the context of epinephrine and the fight or flight response, each liver cell that receives the epinephrine signal will mobilize uncountable numbers of enzymes, so that in seconds glucose is coursing into the blood, on its way to your muscles.

I’ll explain the details of amplification in the next section. The last point for now is that as quickly as cAMP can be released, it can also be deactivated. This happens through an enzyme called phosphodiesterase (shown at “5” below). Phosphodiesterase converts cAMP (“4”) to plain old AMP (“6”). That deactivation of cAMP can shut down a fight or flight reaction almost as quickly as it got started. This can also be essential for survival, because you wouldn’t want to continue to dump glucose into the blood when it’s not necessary. What makes evolutionary sense is to only break down glycogen when you need it.

To consolidate what you’ve learned about signal transduction and cAMP, take the quiz below.

2. Signal Transduction Quiz 1

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Signal Transduction and cAMP (M11)” style=”width: 600px !important;”]

[h] Quiz: Signal Transduction and cAMP

[i]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|6311ae923c7ff” question_number=”1″] In the diagram below, which number represents the ligand?

[textentry single_char=”true”]

[c*] 1

[f] Yes. “1” is the ligand, the molecule that binds with a receptor to set off a cellular response.

[c] *

[f] No. Here’s a hint. A ligand is a molecule that binds to another (usually larger) molecule. In this diagram, what’s about to bind with something larger?
[!!!]+++question 25++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|630c26f5fefff” question_number=”2″] In the diagram below, which number represents the receptor?

[textentry single_char=”true”]

[c*] 2

[f] Yes. “2” is the receptor.

[c] *

[f] No. Here’s a hint. The receptor receives a signal from outside the cell. If the color blue represents the cell exterior and beige represents the cytoplasm, then what’s the only thing in the membrane that is about to connect with something outside of the cell?
[!!!]+++question 26++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|63067a19033ff” question_number=”3″] In the diagram below, which number represents the G protein?

[textentry single_char=”true”]

[c*] 3

[f] Yes. “3” represents the G protein.

[c] *

[f] No. Here’s a hint. The G protein gets activated by the receptor (which itself has been activated by the ligand). Then the G protein activates a membrane bound enzyme (shown at “5”). Which is the only part of the system above that could be activated by the receptor, and in turn, activate the membrane-bound enzyme at “5?”
[!!!]+++question 27++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|6300f27cc5bff” question_number=”4″] In the diagram below, which number represents adenylyl cyclase (the enzyme that converts ATP to cyclic AMP)?

[textentry single_char=”true”]

[c*] 5

[f] Yes. “5” is adenylyl cyclase.

[c] *

[f] No. Here’s a hint. Adenylyl cyclase is a membrane-bound enzyme that converts ATP to cyclic AMP. What’s the only part of the system above that looks like a membrane-bound enzyme that’s converting one thing into another thing?
[!!!]+++question 29++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|62f69d8801fff” question_number=”5″] In the diagram below, which number represents the second messenger cAMP?

[textentry single_char=”true”]

[c*] 7

[f] Yes. “7” represents cAMP (cyclic AMP) a second messenger.

[c] *

[f] No. Here’s a hint. Cyclic AMP is the second messenger. It takes the initial signal (from the ligand, shown at “1”) and transmits it into the cytoplasm. Which part of the system above is sending information forward from the membrane into the cytoplasm?
[!!!]+++question 31++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|62f115ebc47ff” question_number=”6″] In the diagram below, which number represents the ATP that adenylyl cyclase converts into cAMP?

[textentry single_char=”true”]

[c*] 6

[f] Yes. “6” is the ATP that the adenylyl cyclase enzyme (shown at “5”) converts into cyclic AMP.

[c] *

[f] No. Here’s a hint. Cyclic AMP is the second messenger that transmits a signal received by a receptor in the membrane into the cytoplasm. Cyclic AMP is a modified form of ATP. See if you can identify which molecule in the system above could qualify as a second messenger, and then find its precursor form (which is ATP).
[!!!]+++question 32++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|62ebb390453ff” question_number=”7″] If the diagram below were about a liver cell being stimulated by the hormone epinephrine to produce glucose from glycogen, which number would represent epinephrine?

[textentry single_char=”true”]

[c*] 1

[f] Yes. “1” is epinephrine, the signal that brings about the changes that lead this liver cell to convert its glycogen stores into glucose.

[c] *

[f] No. Here’s a hint. If epinephrine is the signal that is received by the cell, what’s the only part of the system above that could represent this signal?
[!!!]+++question 33++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|62e67675843ff” question_number=”8″] If the diagram below were about a liver cell being stimulated by the hormone epinephrine to produce glucose from glycogen, which number would represent conversion of glycogen into glucose?

[textentry single_char=”true”]

[c*] 9

[f] Yes. “9” is the cellular response, which in this case involves the cell converting its glycogen stores into glucose.

[c] *

[f] No. Here’s a hint. Production of glucose from glycogen is the cellular response. The response is the last thing that happens in this system.
[!!!]+++question 34++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|62e0c998887ff” question_number=”9″] In the diagram below, what number represents cyclic AMP (cAMP)?

[textentry single_char=”true”]

[c*] 4

[f] Yes. “4” is cyclic AMP, the second messenger in many cell communication systems.

[c] *

[f] No. Here’s a hint. Cyclic AMP, the second messenger in many cell communication systems, is made from ATP (adenosine triphosphate). So find ATP (with three phosphates) and follow the diagram to find cAMP.
[!!!]+++question 35++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|62db41fc4afff” question_number=”10″] In the diagram below, what number represents adenylyl cyclase?

[textentry single_char=”true”]

[c*] 2

[f] Yes. “2” is adenyl cyclase, the enzyme that creates the second messenger cyclic AMP from its precursor, ATP.

[c] *

[f] No. Here’s a hint. Find the enzyme that converts ATP (with three phosphates) to cyclic AMP.
[!!!]+++question 36++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Signal Transduction (Cell Communication)|62d5dfa0cbbff” question_number=”11″] In the diagram below, what number represents phosphodiesterase?

[textentry single_char=”true”]

[c*] 5

[f] Yes. “5” is phosphodiesterase, the enzyme that deactivates cAMP (“4”) by converting it into AMP (“6”)

[c] *

[f] No. Here’s a hint. Find the enzyme that converts cyclic AMP to AMP.

[x][restart]

[x]

[restart]

[/qwiz]

3. Signal Transduction through Phosphorylation Cascades Results in Signal Amplification

Now, let’s take a more detailed look at transduction, focusing on generating cytoplasmic responses. In the next tutorial, we’ll look at activation of genes.

A key process that occurs as messages move from the membrane into the cytoplasm is phosphorylation, which is what happens when an enzyme adds a phosphate group to a molecule. You’ve seen phosphorylation before in the context of cellular respiration: it’s what happens when ADP receives a third phosphate group, creating ATP. It also happens (among other places) during the investment phase of glycolysis, when enzymes convert glucose into glucose-6-phosphate.

In the context of cell communication, enzymes called kinases phosphorylate proteins. In the same way as you can think of ATP as being more active than ADP, a phosphorylated protein can be thought of the activated form of that protein.

Just to have an picture of what happens during phosphorylation, consider the image below:

The enzyme at “1” is a kinase. It takes an unphosphorylated protein (at “2”) and adds a phosphate to it, converting it into a phosphorylated form (at “3”). The source of the phosphate is ATP (“4”), which becomes ADP (“5”) as a result of having lost a phosphate group.

In cell communication, often the protein that gets phosphorylated by a kinase enzyme is itself a kinase. So what happens within a cell (like a liver cell) as it transduces a hormone signal into its cytoplasm is what’s called a phosphorylation cascade. cAMP gets the process started by activating the first kinase, and that one phosphorylates a second kinase, which activates a third, and so on. Here’s a diagram depicting the process.

You should already be familiar with 1 through 5 in the diagram, so we’ll start with “a,” which is cAMP. When cAMP contacts protein kinase “b,” that kinase is changed into its activated form, “c.” Because “c” is also a kinase, it will activate “d,” changing it into its active form, “g.” Note the little knob hanging off “g.” It’s a phosphate group. This phosphate group was donated by an ATP molecule, represented by “e.” The ADP that results is represented by “f.”

Because “g” is also a kinase, it will phosphorylate “j,” creating its activated form, “k.” Finally “k” will activate molecule “l,” which becomes “m.” In the case of epinephrine getting liver cells to break down glycogen and release glucose, you can imagine that “m” is exactly the enzyme that does that. Letter “n” represents the cellular response, which is production of glucose, which will diffuse out of these liver cells and into the bloodstream.

You might have noticed that there are still two parts of the diagram that we haven’t dealt with: letters “h” and “i.” Letter “h” represents a type of enzyme called a protein phosphatase: these enzymes remove phosphates from kinases, deactivating them. As they do, they release a phosphate group into the cytoplasm, and that phosphate is represented by letter “i.”

Now we can talk about signal amplification. Look again at the diagram, and imagine that cAMP isn’t just activating one molecule of the protein kinase represented by “b.” It’s converting many. Similarly, kinase “c” is converting many molecules of kinase “d” into “g.” The same is happening with “j” and “k” and with “l” and “m.”

So, when you create a mental image of a phosphorylation cascade, don’t imagine a single row of dominoes falling. Instead, think of an exponentially growing response. In the video below, Professor Chris Bishop has set up 100 ping pong balls on mouse traps. Each one of those traps is the equivalent of the dormant enzymes in a liver cell, waiting to be set off. Watch what happens in response to a small signal…a single ping pong ball.

Here’s an image that’s trying to communicate the same idea:

The hormone (at “1)” binds with a membrane receptor (“2”), which activates a membrane embedded enzyme (“3”) such as adenylyl cyclase. That enzyme activates a few second messengers (at “4”). Each second messenger will activate a few kinases (“5”), and each of these kinases will now activate multiple enzymes at the end of this chain (indicated by “6”).

One signal came in, and 18 enzymes have been activated as part of the cellular response.

The graphic above, however, doesn’t nearly do justice to how amplified a cytoplasmic response can be. Study the diagram to your right. Notice that in each transition, the response might be amplified 10 or 100 times. A single epinephrine molecule might, in the end, be responsible for the release of 100 million glucose molecules…and that’s just one hormone binding to one receptor in one cell. Now think about the fact that there are hundreds of millions of liver cells, each of which has hundreds or thousands of receptors.

And that, of course, is also the reason why the cell needs to able to turn these responses off as quickly as they were started. That’s why the cell has enzymes like phosphodiesterase to deactivate cAMP, and protein phosphatases to deactivate protein kinases.

While there are other systems to generate cytoplasmic responses, we’re going to limit this discussion to just G-protein coupled receptors, and the type of phosphorylation cascades we’ve just studied. In the next tutorial, we’ll address how other hormonal signals can generate longer lasting, more permanent responses in cells by activating genes.

For now, let’s consolidate the learning we’ve done with a quiz.

4. Quiz: Kinases, Phosphorylation Cascades, and Signal Amplification

[qwiz random=”true” qrecord_id=”sciencemusicvideosMeister1961-Kinases, Phosphorylation Cascades, Signal Amplification (M11)”] [h]

Kinases, Phosphorylation Cascades, and Signal Amplification

[i]

[!!!]+++question 37++++++[/!!!!]
[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62c15af8027ff” question_number=”1″] If molecule 2 is a protein, then which number represents a protein kinase?

[textentry single_char=”true”]

[c*] 1

[f] Yes. “1” is a protein kinase. Protein kinases are enzymes that phosphorylate proteins.

[c] *

[f] No. Here’s a hint. Protein kinases are enzymes that phosphorylate proteins (add a phosphate group to them, which alters their activity). In the diagram above, what is converting a protein into its phosphorylated form?
[!!!]+++question 38++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62ba5ed4567ff” question_number=”2″] In the diagram below, which number represents a phosphorylated protein?


[textentry single_char=”true”]

[c*] 3

[f] Yes. “3” is a protein that has been phosphorylated by a protein kinase (shown at “1”). You can tell it’s been phosphorylated because of the attached phosphate group (the “P” inside a yellow circle).

[c] *

[f] No. Here’s a hint. You can tell if a protein has been phosphorylated if it has a phosphate group attached. Take a good look at the diagram above, and find the phosphorylated protein.
[!!!]+++question 39++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62b25deb76bff” question_number=”3″] In the diagram below, which number represents the molecule that provided the phosphate that the protein kinase (1) used to phosphorylate molecule 2 into molecule 3?

[textentry single_char=”true”]

[c*] 4

[f] Yes. “4” represents ATP. Protein kinases take a phosphate from ATP and plant it on another substrate molecule, phosphorylating it.

[c] *

[f] No. Here’s a hint. Protein kinases plant phosphates onto a protein. To do that, they need a phosphate “donor.” Find a molecule that loses a phosphate so that another molecule can gain a phosphate, and you’ll have the answer.
[!!!]+++question 40+++START PHOSPHORYLATION CASCADE+++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62ac668cfe7ff” question_number=”4″] In the diagram below, which letter represents cyclic AMP?

[textentry single_char=”true”]

[c*] a

[f] Yes. Letter “a” represents cyclic AMP.

[c] *

[f] No. Here’s a hint. Cyclic AMP is the second messenger that moves the signal from the membrane into the cytoplasm. In the diagram above, which is the only molecule that could be playing that role?
[!!!]+++question 41++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62a66f2e863ff” question_number=”5″] In the diagram below, which letter represents the inactive form of protein kinase 1?

[textentry single_char=”true”]

[c*] b

[f] Yes. Letter “b” represents the inactive form of protein kinase 1.

[c] *

[f] No. Here’s how to think about this. Letter “a” is cAMP, the second messenger. cAMP binds with an inactive form of protein kinase 1, resulting in a phosphorylated (phosphate containing) version of this molecule (which you can see at “c”). Look at the diagram, and try to figure out what molecule cAMP (at “a”) must be interacting with to bring this about.
[!!!]+++question 42++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62a02d4e917ff” question_number=”6″] In the diagram below, which letter represents the active form of protein kinase 2?

[textentry single_char=”true”]

[c*] g

[f] Yes. Letter “g” represents the active form of protein kinase 2.

[c] *

[f] No. Here’s how to think about this. Letter “a” is cAMP, the second messenger. cAMP binds with an inactive form of protein kinase 1 (at “b”), resulting in a phosphorylated (phosphate containing) version of this molecule: the active form of protein kinase 1 (which you can see at “c”). Look at the diagram, and try to figure out what molecule must be the activated (phosphorylated) form of protein kinase 2.
[!!!]+++question 43++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|6299c62dde7ff” question_number=”7″] In the diagram below, which letter represents the enzyme that converts the phosphorylated kinases into their inactive forms?

[textentry single_char=”true”]

[c*] h

[f] Yes. “h” represents the enzyme (a protein phosphatase) that transforms phosphorylated kinases (such as those at “g,” and “k,” to their unphosphorylated forms (such as those at “d” and “j.”)

[c] *

[f] No. Here’s how to think about this. Focus on molecule “g.” It’s a phosphorylated kinase. Notice that “g” was made by phosphorylating molecule “d,” and that “g” can be converted back to “d.” Based on what you see in the diagram, what’s the enzyme that converts “g” back to “d” (or “k” back to “h”)?
[!!!]+++question 44++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|6293cecf663ff” question_number=”8″] In the diagram below, which letter represents the inactive form of the target protein that’s going to bring about the cellular response?

[textentry single_char=”true”]

[c*] l

[f] Yes. Letter “l” represents the inactive (unphosphorylated) form of the target protein.

[c] *

[f] No. Here’s how to think about this. The ultimate cellular response is indicated by letter “n.” This cellular response is brought about at the end of this phosphorylation cascade. What molecule needs to be phosphorylated to create “m?”
[!!!]+++question 45++++++[/!!!!]

[c] Enter letter

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|628dd770edfff” question_number=”9″] In the diagram below, which letter represents the ATP that’s used during a phosphorylation cascade?

[textentry single_char=”true”]

[c*] e

[f] Yes. Letter “e” represents ATP, the source of the phosphate used to phosphorylate the protein kinases in this phosphorylation cascade.

[c] *

[f] No. Here’s how to think about this. In phosphorylation cascades like the one represented above, protein kinases activate other proteins (which can also be kinases) by adding phosphates to them. The phosphate group is taken from ATP, which becomes ADP as it loses a phosphate. So look at molecule “d” and “g.” What symbol lies in between? You’ll find the same symbol between “j” and “k,” and even between “l” and “m.”
[!!!]+++question 46++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|6287e01275bff” question_number=”10″] Phosphorylation cascades like the one shown below need to be quickly activated, and also quickly deactivated. Which letter indicates a protein phosphatase, the enzyme that takes activated, phosphorylated molecules and deactivates them by removing a phosphate group?

[textentry single_char=”true”]

[c*] h

[f] Yes. “h” represents a protein phosphatase, the deactivating enzyme in this phosphorylation cascade.

[c] *

[f] No. See if you can find a letter that represents an enzyme that would convert a phosphorylated kinase such as “g” back into its unphosphorylated form at “d.” The same enzyme is at work between “k” and “j” or “m” and “l.”
[!!!]+++question 47++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|6282333579fff” question_number=”11″] In the diagram below, the ligand is represented by which number?

[textentry single_char=”true”]

[c*] 1

[f] Yes. “1” the ligand.

[c] *

[f] No. The ligand is the molecule that binds with the receptor, setting off the reaction that results in a cellular response. If “2” is the receptor, what has to be the ligand?
[!!!]+++question 48++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|627bf155853ff” question_number=”12″] In the diagram below, which number represents the receptor?

[textentry single_char=”true”]

[c*] 2

[f] Yes. “2” is the receptor.

[c] *

[f] No. The receptor is the membrane-bound molecule that binds with the receptor. Find the membrane, and you’ll be able to figure out which part has to be the receptor.
[!!!]+++question 49++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|627564f413fff” question_number=”13″] Assume the diagram below represents how the hormone epinephrine stimulates liver cells to release glucose. Which number would represent adenylyl cyclase?

[textentry single_char=”true”]

[c*] 3

[f] Yes. “3” would represent adenylyl cyclase.

[c] *

[f] No. Here’s a hint. In the scenario described above, adenylyl cyclase is a membrane-bound enzyme that activates the second messenger cAMP. Looking at the diagram, what’s the only component at this system that could be a membrane-bound enzyme?
[!!!]+++question 50++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|626f4854dd7ff” question_number=”14″] Assume the diagram below represents how the hormone epinephrine stimulates liver cells to release glucose. Which number would cyclic AMP?

[textentry single_char=”true”]

[c*] 4

[f] Yes. “4” would represent the second messenger, cyclic AMP.

[c] *

[f] No. Here’s a hint. “1” is the signal, making it the “first messenger.” Cyclic AMP, the second messenger, is released from the membrane to set up reactions inside the cytoplasm. What’s the only part of the system above the could qualify as a “second messenger?”
[!!!]+++question 51++++++[/!!!!]

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|6265d2e48f3ff” question_number=”15″] Assume the diagram below represents how the hormone epinephrine stimulates liver cells to release glucose. If “4” represents cyclic AMP, then what number would have to be protein kinase?

[textentry single_char=”true”]

[c*] 5

[f] Yes. “5” would represent protein kinase.

[c] *

[f] No. Here’s a hint. Protein kinases are activated as part of a phosphorylation cascade that results in a massively amplified cellular response. Find the number that’s in between the second messenger cAMP and the cellular response.

[c] Enter letter

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|626070890ffff” question_number=”16″] In the diagram below, letters c, g, and k represent activated protein[hangman]

[c] kinases

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|625ac3ac143ff” question_number=”17″] If the diagram below was about breakdown of glycogen in liver cells, then letter “n” would represent  [hangman].

[c] glucose

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62541209e4bff” question_number=”18″] The diagram below depicts a phosphorylation [hangman].

[c] cascade

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|624e1aab6c7ff” question_number=”19″] If the diagram below was about breakdown of glycogen in liver cells, then number  1 would represent the hormone [hangman]

[c] epinephrine

[q json=”true” dataset_id=”SMV_Kinases, Phosphorylation Cascades, Signal Amplification (cell communication)|62468984c77ff” question_number=”20″] In the diagram below, letter “a” represents cyclic [hangman]

[c] AMP

[x][restart]

[/qwiz]

5. Conclusion: this is just one example of hormone action…

As we’ve learned about cell communication, I’ve kept the focus on polar hormones like epinephrine, and how epinephrine induces liver cells to convert glycogen into glucose as part of the fight or flight response. Here are a few things to keep in mind, however, before we leave this topic.

  1. Hormones like estrogen, testosterone, and thyroid hormones are lipid-soluble, and work by a different mechanism. We’ll look at this mechanism in the next tutorial.
  2. There are many different mechanisms by which polar hormones bind with membrane receptors, and there’s a similar degree of variety in which the signals brought by these hormones are transduced through second messengers to bring about cytoplasmic changes. If you’re preparing for a test, be sure that you know the mechanism that your instructor is going to teach you about (although, hopefully, it will be the G-protein coupled receptors that we’ve looked at here).
  3. Through their receptors, cells are “tuned” to respond to specific ligands (in much the same way that a radio will pick up a specific station’s signal only when it’s tuned to the right frequency). However, a hormone might have a variety of targets throughout the body, and these targets, depending on the tissues that they’re a part of and their internal structure and chemistry, might respond to the hormone in different ways. To turn back to our example of epinephrine, it has a variety of effects throughout the body.
    1. In the liver (as we’ve seen), epinephrine induces liver cells to break down glycogen into glucose
    2. In the smooth muscle tissue that lines the arteries that supply the intestines and the rest of the digestive system with blood, it induces muscle contraction. This reduces the diameter of these arteries, and slows down the flow of blood to the digestive tract, which frees the body to divert blood away from the digestive system and towards the muscles of the skeletal system. From a survival perspective, the first priority has to be getting away from that predator. You can digest your lunch when you’re safe (or, if you’ve vomited out your lunch because of fear, you can find more food to eat at a later time).
    3. In the smooth muscle surrounding the arteries that supply the muscles with blood, it causes muscle relaxation. This opens up these blood vessels, increasing the amount of blood that flows to the muscles: a useful adaptation if you’re escaping from or fighting off a predator.
  4. SUMMARY: one hormone, different effects. We’ll see this again in our study of steroid hormones in the next tutorial.

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