What citric acid cycle intermediates are precursors to amino a...

Question

What citric acid cycle intermediates are precursors to amino acids?

Accepted Answer

Hi, everybody. Welcome back. Let's look at our next question. Which of the following statements regarding TC A cycle intermediates serving as precursors to amino acids is or are true. And then we have four statements, one through four and then four answer choices A through D with different options about which of these statements are true. So let's work our way through each of these statements thinking about the connection between the TC A cycle and amino acid synthesis. So first off, let's recall that TC A cycle is a less common name for the citric acid cycle or crab cycle. TC A is standing for tr carboxylic acid cycle. So the intermediate of this cycle can indeed act as precursors to amino acid synthesis steps. Along the way, we can help remember this because we know that proteins themselves in cases of, for instance, starvation when there's not a carbohydrate energy source around can be broken down for energy. Although that's, you know, not their most common fate when they're broken down because those amino acids can be changed into citric acid cycle intermediates. So it can go both ways. So let's think about these connections here and what specifically is connected. So we have two citric acid cycle intermediates that are precursors and those two are alpha ketoglutarate and oxalacetate. So let's look at our answer choices and work our way through. So statement one says malate is directly used to synthesize the amino acid aspartate. Well, this statement is incorrect. We'll cross that out. Mallet is the wrong uh precursor for aspartate aspartate comes from the transamination of oxalacetate. Our clue here would be is that as we just reminded ourselves, the cycle intermediates we're looking at are alpha ketoglutarate and oxalacetate. So we could just rule that out seeing malate in there. Statement two says succinate is a precursor for the synthesis of glutamine. Well, succinate isn't one of the two intermediates that we talked about. Number two is incorrect. The priest's rec cursor for the synthesis of glutamine is as you might guess, alpha ketoglutarate. Now this route goes through glutamate. So alpha ketoglutarate is used to synthesize glutamate and then that goes through reaction to be change and to glutamine. But succinate is not the precursor there. Alpha ketoglutarate is the citric acid cycle intermediate. That's the precursor. So we've eliminated one and two. That lets us eliminate choice D 23 and four, but no other choices. Stephen three says oxalacetate is used to synthesize sine. So oxalacetate, that's one of the intermediates we use. But this statement is still incorrect because sine is not one of the amino acids derived from oxalacetate. So, oxalacetate is a precursor for a number of amino acids uh including aspartate as we discussed in statement one, when we were looking at that, but seine is not one of them. So now we've eliminated number three just by elimination, we've got statement four as our true statement. Since we eliminated three, we can cross out choice A which is three only and choice C which is three and four. And we know our answer choice must be choice B four only. So that's just to be thorough. Look at choice four or statement four which is alpha ketoglutarate is a precursor for the synthesis of glutamate. Well, we already discussed that when we looked at statement two, it is indeed a precursor for the synthesis of glutamate. And this glutamate itself is a precursor for the synthesis of a number of other amino acids including glutamine as we mentioned. So once again, the statements regarding the TC A cycle intermediates that serve as precursors to amino acids. The statements that is or are true, there's only one of them. And that's statement four, alpha ketoglutarate is a precursor for the synthesis of glutamate. So our answer is choice B four only hope to see you in the next video.

What citric acid cycle intermediates are precursors to amino acids?

Key Concepts

Citric Acid Cycle (Krebs Cycle)

Amino Acid Biosynthesis

Metabolic Intermediates

Watch next