Practice - Bioenergetics 1 - Online Tutor, Practice Problems & Exam Prep

Signal transduction systems exhibit five key features: specificity, amplification, modularity, adaptation, and integration. Specificity ensures precise interactions, while amplification allows a single signal to produce a large response. Modularity enables proteins to interact with various pathway components. Adaptation involves feedback mechanisms that adjust responses, and integration coordinates multiple signals for appropriate cellular responses. In bioenergetics, a reaction with $\mathrm{\Delta G}<0$ and $K>1$ proceeds spontaneously, while a positive $\mathrm{\Delta G}$ indicates non-spontaneity.

Practice - Bioenergetics 1

If you haven't yet tried question 8, pause the video now and give it a shot. The 5 major features of signal transducing systems are specificity, amplification, modularity, adaptation, and lastly integration. Now, the question asks for just these names, but let's talk about what each one means again. So, specificity is like we've seen with all the proteins we've looked at up to this point. You know, these proteins have specific interactions, and the signals that they're using are generally chemical in nature. Amplification. Remember like, with our example of epinephrine. One molecule of epinephrine binding to a receptor can lead to 100,000 molecules of glucose, right? So that signal can get super amplified, and it gets amplified basically each step of the way on the signal pathway. Modularity. Proteins are able to interact with multiple components of the pathway, right? They can interact with the signal and also then interact with the receptor. Adaptation. Right? These signal pathways are able to attenuate their response, right? So you'll have some sort of feedback from the signaling pathway that for example, will remove, and then, you know, using the example of epinephrine again, you know, where we'll, have feedback that will actually remove epinephrine receptors from the membrane to attenuate that cell's response to the ligand epinephrine. So, these signaling pathways adapt, right? That's the important feature. And then lastly integration. Remember that figure with all the different systems coming and intersecting? Remember talking about crosstalk. There's so many different signal pathways that are all going on all at the same time, and those signals have to integrate together so that the cell comes up with the appropriate responses.

Now, let's flip our attention over to bioenergetics. Taking a look at question 9, if Keq>1 and ΔG is negative for a particular reaction done at standard conditions, in which direction will the reaction proceed? Well, it will proceed forward, and let's just take a look at this. So if Keq>1 that means that remember Keq, we're looking at the rate of formation of products over the rate of disappearance of reactants. So if there's a greater rate of formation of products, that means that our Keq will be greater than 1. However, if our Keq<1, that means that there was more the rate of formation of reactants was greater than the rate of formation of products, meaning that you know, that the sort of the, in terms of the kinetics of that reaction, it's looking in the reverse direction. And lastly, if Keq=1. What do you think that means? What do you think it means if the rate of formation of our products is the same as the rate of formation of our reactants? Well, that means that we're at important to also consider your delta Gs here. So, if Keq>1 and ΔG is negative or just put that out front actually, right? That makes more sense. Negative ΔG. That means that you have a reaction that is going to spontaneously proceed forward. So this is going to go forward. If your Keq=1 and your ΔG is equal to 0, again, you are at equilibrium. And lastly, if your ΔG is positive and your Keq<1, you're going to go the reverse direction. So, in this case, we have these conditions up top meaning our reaction is going to proceed forward. Alright. Let's look at question 10. Which of the following is not correct? The answer here is E, phosphocreatine. Phosphocreatine has a ΔG that's basically negative 43 kilojoules per mole. Meaning, it's actually greater than that of ATP because ATP you might recall is about 30 kilojoules per mole. So phosphocreatine actually is a, a greater ΔG than ATP or a more negative ΔG, I should say. And yeah. A through D, these are all correct value ranges. Now, let's take a look at 11. ΔG on the reaction, studentose 2 protocate is negative 35 kilojoules per mole. This means that under standard conditions, the reaction will What does it mean if we have negative ΔG? What does ΔG tell us about a reaction? It tells us whether or not a reaction will occur spontaneously. It doesn't indicate how fast that reaction is going to proceed though. So, that's a big important difference to keep in mind that ΔG just tells you whether or not it's going to happen spontaneously, meaning whether or not it's going to happen on its own. It doesn't mean it will happen quickly. There are a lot of spontaneous reactions that are incredibly slow. So, our answer here is E, will proceed spontaneously from student host to protagonist. If it was positive, then it would not occur spontaneously. And if it was 0, it would be at equilibrium. So let's move on to question 12. Which of the following has the largest negative value for ΔG of hydrolysis? So this is very similar to question 10, right? Now, we're almost doing the opposite of question 10 here, right? So, what has the largest negative value for hydrolysis and of the molecules listed, it is acid anhydrides. And remember, those range from about negative 30 to 40 kilojoules per mole and that includes ATP. ATP is an acid anhydride. All right. Let's take a look at question 13. So, let's consider the malate dehydrogenase reaction. We have a ΔG in the positive range and this reaction takes malate and NAD+ and turns into oxaloacetate and NADH and we're actually going to take a look at this reaction much more detail in the next unit. We talk about the citric acid cycle but for now, looking at this, what is the answer here? The reaction as written may actually occur at some concentrations of substrates and products, in certain cells. Now, remember back to our glycolysis reactions. We had that one reaction that at these biochemical conditions, ΔG prime not, it had a positive ΔG, right? But at cellular conditions, Its ΔG was closer to 0, right? So bear in mind that the reaction they're showing us, they're saying that ΔG not prime though. That has a positive value but it's possible. We don't know. It's possible that in cells at certain concentrations of substrates and products, this ΔG might actually be closer to 0 or even negative. So, it's we don't know that it can never occur can occur if it's coupled with a positive ΔG prime reaction. And can occur cannot occur at all because of its activation energy and does not even occur in biochemics. No way. So May occur depending on the conditions in the cell and think about that reaction that we we talked about before that had a positive ΔG in these conditions but in cellular conditions actually had ΔG closer to 0. Alright. Let's flip the page.

Here’s what students ask on this topic:

What are the five major features of signal transducing systems?

The five major features of signal transducing systems are specificity, amplification, modularity, adaptation, and integration. Specificity ensures that signals interact precisely with their target proteins. Amplification allows a single signal molecule to produce a large response, as seen with epinephrine leading to the production of many glucose molecules. Modularity refers to the ability of proteins to interact with multiple components within the signaling pathway. Adaptation involves feedback mechanisms that adjust the cell's response to a signal, such as removing receptors from the membrane. Integration coordinates multiple signals to produce an appropriate cellular response, ensuring that the cell can process and respond to complex information.

How does the value of ΔG determine the spontaneity of a reaction?

The value of ΔG (Gibbs free energy change) determines whether a reaction will occur spontaneously. If ΔG is negative (ΔG < 0), the reaction is spontaneous and will proceed without external energy input. If ΔG is positive (ΔG > 0), the reaction is non-spontaneous and requires energy to proceed. When ΔG is zero (ΔG = 0), the reaction is at equilibrium, meaning the rates of the forward and reverse reactions are equal, and there is no net change in the concentrations of reactants and products.

What does it mean if Keq is greater than 1 for a reaction?

If the equilibrium constant (Keq) is greater than 1, it indicates that the rate of formation of products is greater than the rate of formation of reactants. This means that, at equilibrium, the concentration of products is higher than that of reactants. In terms of Gibbs free energy, a Keq greater than 1 typically corresponds to a negative ΔG, suggesting that the reaction proceeds spontaneously in the forward direction under standard conditions.

What is the significance of ΔG in bioenergetics?

In bioenergetics, ΔG (Gibbs free energy change) is crucial for understanding the energy changes associated with biochemical reactions. A negative ΔG indicates that a reaction can occur spontaneously, releasing energy that can be harnessed by the cell. Conversely, a positive ΔG means the reaction is non-spontaneous and requires an input of energy. ΔG helps predict whether a reaction will proceed and is essential for understanding metabolic pathways and energy transfer within cells.

How does the concept of amplification work in signal transduction?

Amplification in signal transduction refers to the process where a single signal molecule triggers a cascade of events, leading to a large cellular response. For example, one molecule of epinephrine binding to its receptor can activate multiple G-proteins, each of which can activate several adenylyl cyclase enzymes. This results in the production of many cAMP molecules, which then activate numerous protein kinase A molecules, ultimately leading to the release of a large number of glucose molecules. This amplification ensures that even a small signal can have a significant impact on the cell.