In the liver, the relative activity of ornithine transcarbamylase is high, that of argininosuccinate synthetase is low, and that of arginase is high. Why is it important that ornithine transcarbamylase activity be high in the liver? What might be the consequence if arginase activity is low or defective?

Question

Accepted Answer

Hi, everybody. Welcome back. Let's take a look at our next question in the liver, the relative activity of ornithine, trans caramella and Argena is lower than that of Argen succinate synthetase. Is this statement? True or false? A true or be false? So, we've got a whole mouthful of words here. Let's sort out what these do and think about what this statement would mean true or false. So we have enzymes here that are all involved in the urea cycle. So before this cycle really starts, recall that the whole purpose of this is to go from ammonia to urea, your ammonia is toxic. You want to convert it to urea that can be eliminated from the body. So before the cycle really begins, you have ammonia, you have ammonia and carbonic acid with the help of two A TPS being converted and producing the product of carb oil phosphate. This product will then combine with ornithine and the first step of the cyclical part of this whole process. This step is going to be catalyzed by the enzyme ornithine trans carb amylase, which I'm going to write as OTC. So I don't have to write out that entire giant name. But we can see that that is up here in our problem if we want to refer back to it. So there's our, I'm going to get a highlight so we can sort of match it. So we'll do in pink ornithine trans carmela. And then this step it's in here. So we can kind of keep track as we evaluate the problem at the end. So there is our kind of first step in the cyclical process. So then what this produces is cle and phosphate. I put phosphate in parentheses because then our cle is going to combine with aspartame and at P and this step is going to be catalyzed with the enzyme Argen succinate synthetase, which we will and the highlighting in green of the step here and the enzyme since this is another enzyme mentioned in our question. So after this step, we unsurprisingly have the product and our enzyme is called Argen Suint synthetase. We've synthesized Argen Suint and we have the enzyme Argen Suena, which is going to catalyze the splitting of our product here into arginine and fumarate. This step will also produce water and then the enzyme that's going to catalyze. The next reaction is the last one that our question asks asks about which is our Gena. So we'll get you another highlighting color. Let's go ahead and highlight this one in blue or actually, we'll highlight in yellow. So we've got our reaction here with arginine catalyzed by arginase and arginase is the last enzyme we're asking about here. And in the final step of that cycle that arginine is converted into urea and or a the thus, we see the cyclical nature of this is weve regenerated the or the. So now we want to think about what does this mean for evaluating the statement that in the liver, the activity of ornithine trans carmela. So that very first step and arginase or last step would be lower than arginine nosy thease. So let's I'm going to put a down arrow on our first pink step there, down arrow on the last, yeah, second to last yellow step and an up arrow on the uh geno succinate sympathy. And think about what it would mean if this is how the levels were. Well, the very first step is where we have that product of the conversion of urea. So you've got or excuse me, wrong end of the cycle conversion of ammonia. So, ammonia is converted into carbon oil phosphate and then the OTC will catalyze the next step. So if this activity level is low, we are not going to keep processing that ammonia through the cycle. So that would be a bad thing. If this step is not functioning properly, you'll end up having a build up of ammonia. In addition, our final step is what's leading to the production of urea. Without this step operating efficiently, we won't be producing urea and then the ornithine to go back into the cycle that we need. So both of these steps, one and four are quite important just for maintaining the ammonia being just ticking along, being converted, not building up and then keeping the cycle going by producing the end products. Compared to that, this middle step with the Argen succinate of the taste is not as crucial to have high levels of the enzyme. So the question that's proposed to us about this hypothetical situation with these particular enzyme activities is exactly reverse what you'd expect to see. So our answer choice here is going to be choice B false. So our statement is false since we would expect the reverse of what it proposes to us to you in the next video.

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Key Concepts

Ornithine Transcarbamylase (OTC)

Urea Cycle

Arginase