A. If the biosynthesis of palmitic acid were carried out...

Key Concepts

Fatty Acid Biosynthesis

Fatty acid biosynthesis is the metabolic process by which organisms generate fatty acids such as palmitic acid through a series of iterative condensation reactions. In these reactions, a starter unit (usually acetyl-CoA) is first combined with an extender unit (usually malonyl-CoA) to progressively build the carbon chain through repeated cycles of condensation, reduction, dehydration, and reduction steps.

Chain Elongation Mechanism

The chain elongation mechanism in fatty acid synthesis involves the sequential addition of two-carbon units from malonyl thioesters. Each elongation cycle involves a decarboxylation step that contributes to the formation of a carbon–carbon bond, followed by a series of modifications that convert the intermediate into a fully saturated fatty acid structure. This mechanism is key to determining how isotopic labels from the extender units are retained or lost during synthesis.

Isotopic Labeling

Isotopic labeling is a technique in which atoms in a molecule are replaced with their isotopic forms, such as deuterium in place of hydrogen, to trace the incorporation and transformation of these atoms during chemical reactions. In biosynthetic pathways, this method helps reveal the fate of specific atoms from precursor molecules as they are transported through various enzymatic steps.

Deuterium Incorporation Analysis

Deuterium incorporation analysis involves examining how deuterium atoms from a labeled substrate are integrated into the final product during biosynthesis. This analysis is particularly important in tracking which steps of the biosynthetic pathway maintain the labeled atoms and which steps, such as decarboxylation or exchange reactions, may result in the loss of deuterium. Understanding this allows for detailed mapping of reaction mechanisms and substrate transformations.

Transcript

00:01 Okay, this problem is composed of two questions.

00:02 The first one is asking us if we wanted to synthesize palmatic acid, which is composed of 16 carbons from melanothelester and a deuterated acetyl thylester.

00:11 How many deuterium atoms would we get in our final product of palmitic acid? okay, so that's the first one, and the second one is asking us, same question, except with acetyl thylester and a deuterated malanol thylester.

00:23 Okay, so again, how many deuterium atoms are going to be incorporated into this eventual product of palmitic acid? okay, so let's go ahead and try this out.

00:31 So first up, i know that melanothioster and my so -called duterated acetyl thyloster are going to go ahead and react.

00:38 Okay, that is going to react like this, in which i'll do this in red.

00:42 I'm going to have the electrons from this single bond, stemming from this carbon.

00:47 They're going to go ahead and attack this carbonyl.

00:51 Okay, when they attack that carbonyl, i'm going to have to move the electrons up to this oxygen to form this product in which i have my melanothiolester right here.

01:01 So as we have this, we're going to have to get rid of my co2, because i'm going to move the electrons down from that oxygen to form my co2, and that releases as gas.

01:11 Okay, so this is the carbon that i have the connection to of my duiterated acetyl thyloster.

01:16 Okay, so connected to this carbon, which again is this carbon, i'm going to have the connection to this carbon, which is this carbon.

01:23 Okay, so connected to that carbon is my oxygen with a negative charge, and then we have the three deuterium atoms on this.

01:31 Last carbon, just like that.

01:34 Okay, so eventually the electrons are going to come back down onto this, onto the single bond to create a double bonded oxygen.

01:41 Okay, so that is going to be looking like this, in which you just have the movement of those electrons back down onto here.

01:49 Okay, so that is actually going to undergo a reduction in which we transform this specific carbonyl into an alcohol, and that is because ketones are easier to reduce than thio esters.

02:00 Okay, so after that we should get to this, in which we have an alcohol there.

02:04 Okay, and then we have the carbonyl here slash thioester, and then we have the three deuterium atoms over here, which i'll just represent as cd3.

02:13 Okay, next up is going to be a dehydration in which we essentially get rid of this alcohol, and in the process of doing that, we're going to have to make an alken right here.

02:21 So we're also going to deprotate one of these hydrogens.

02:23 Okay, so that is going to look like this, in which i have the formation of my alken.

02:29 Okay, so i have my thioester over here, sr, i again lost this alcohol, so i don't have that any longer, and i have an alken here with again my cd3.

02:39 Okay, so the very next step is the reduction of this alken into just a straight chain.

02:45 Okay, so it's just going to be a single bond.

02:47 So i'm going to have my cd3, my no longer alken, just an alken, and then i'm going to have my carbonyl slash thiawester.

02:57 Okay, just like that.

02:59 Okay, so again, this is the synthesis of pommantic acid.

03:01 So we have to have 16 carbons total, and so far we only have four.

03:05 But the question is, how many deuterium atoms are going to add to pulmetic acid acid, if we just have the started material of this duiterated acetyl thyloster and my maladal thyloster.

03:16 Okay, so if we identify what our product is after that first round of fatty acid synthesis, i'm going to have only three carbons, or only three deuterium atoms.

03:26 Okay, and then what's going to be next to my synthesis is the incorporation of my melanotheloster.

03:30 Okay, and that melanothioster is going to be incorporated onto this carbonyl.

03:34 Okay, so we're ending up with this.

03:36 This is the start of my extension of my fatty acid, and then we're adding these two more carbons to this side of my molecule.

03:43 So that means that we're not going to be adding any more deuterium atoms, simply because we don't have any deuterium atoms incorporated into melanothioester.

03:51 Right, we only incorporate my deuterated acetyl thioester one time, and that one time is already incorporated right here.

03:58 So that means we're only going to have three deuterium...

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