Use the fossil evidence shown in Figure 25.6 to determine whether...

Question

Use the fossil evidence shown in Figure 25.6 to determine whether flight evolved earlier in insects or in birds. Is flight an example of homology or convergent evolution? Explain. <IMAGE>

Accepted Answer

Hi everyone. Let's look at our next question. It says identify the model for enzyme substrate interaction. That suggests that the enzyme and the substrate have complementary geometric shapes that fit exactly into one another. So, let's look at our answer choices. We'll notice that we've got three different model choices and then Choice C. Says both A and B. So there's a possibility that more than one could be correct. So, again, the key word here is exactly we wanna imagine sort of like our um our substrate and our enzyme fit together. Here's your substrate, here's your little enzyme and it's got this shape that fits exactly with the substrate. Well, that kind of model, as you can imagine, is called the lock and key model. Just as a key fits exactly into a lock. We have the substrate fitting exactly into the active side of the enzyme. So that is the name of the model that we're looking for. But let's just look at our other two model choices and see why they're not the correct answer here. Choice A says the induced fit model. Well, the induced fit model imagines that um here's our substrate, here's our enzyme and it's got an active site that's not quite the right shape for this. So this binds anyway. But then after binding. So this we have it's it's settled in there but not really fitting exactly. We see a confirmation all change in the enzyme where the active site changes shape to fit the substrate more exactly after binding. So we don't have this exact fit in the induced fit model. Instead, we have a change to the active site of the enzyme. So that's why induced fit is not the correct answer here. And that's also why we wouldn't choose choice C. Because A is not correct. And finally, we have the confirmation selection model that's kind of the reverse idea of the induced fit. That says that we have um I'm sorry, not the reverse idea, but it's it's sort of like induced fit but a little different. It involves here's our enzyme with its active site, here's our substrate. Just put a little box here. So we don't get mixed up and they're not an exact fit. But then prior to their binding this enzyme undergoes a conformational change that then changes the active site so that it combined. And the final step then, is this binding of the substrate into the active site that now fits it. But again, we don't have a perfect fit in the beginning. As with the lock and key model, we have a change to the active site immediately prior to the substrate binding with the active site that's called the confirmation selection model. So that's why that is not the correct answer here. We have sort of this this idea, this rigid lock and key model where the two fit together exactly. So which one um reflects that fitting exactly into one another. Again, that's choice B lock and key model. See you in the next video

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