Evidence for the role of acetate in fatty-acid biosynthesis...

Evidence for the role of acetate in fatty-acid biosynthesis comes from isotopelabeling experiments. If acetate labeled with $13 \mathrm{C}$ in the methyl group $\left({ }^{13} \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\right)$ were incorporated into fatty acids, at what positions in the fattyacid chain would you expect the ${ }^{13} \mathrm{C}$ label to appear?

Key Concepts

Isotopic Labeling in Metabolic Pathways

Isotopic labeling, such as using 13C-labeled acetate, is a method for tracing the flow of atoms through metabolic pathways. By labeling specific positions in a precursor molecule, researchers can determine how these atoms are incorporated into complex products like fatty acids, thereby elucidating the detailed mechanism of synthesis.

Decarboxylative Condensation Reaction

A key step in fatty acid synthesis involves decarboxylative condensation, where a malonyl unit condenses with the growing fatty acid chain. The loss of the carboxyl carbon (as CO2) during each cycle means that the surviving carbon atoms are incorporated in a regular, periodic manner, which is critical in interpreting isotope labeling patterns.

Fatty Acid Biosynthesis Mechanism

This concept involves the process by which fatty acids are synthesized, where a two?carbon acetyl unit is first attached as a primer and then sequentially elongated by the addition of two?carbon units derived from malonyl-CoA. Each elongation cycle includes a decarboxylation step that removes one carbon, resulting in a predictable pattern of carbon incorporation along the fatty acid chain.

Acetyl-CoA and Malonyl-CoA Building Blocks

Acetate is activated to form acetyl-CoA, which serves as the primer for fatty acid synthesis, while additional two-carbon units are provided by malonyl-CoA. In the condensation reaction, the carboxyl group from malonyl-CoA is lost as CO2, so only the remaining carbons, originally from the methyl group in acetate if labeled, become part of the fatty acid structure.

Transcript

00:02 Okay, so we're going to start off with acetate.

00:05 And acetate is actually going to be a precursor for acetylcoa.

00:14 So we're just going to add a co -a group onto this.

00:18 And let's mark our carbon duncebin isotope labeled.

00:23 So i'm going to put that in red so we can just follow it as we go through this.

00:29 So acetate adding a co -a, which is going to be.

00:32 Going to take some atp, so we're going to be using atp here.

00:39 And that is going to form acetyl -coa.

00:45 So we have our labeled carbon here, h3, and then we have our acetyl, or our coa group, which is attached using a sulfur.

01:02 Oh, and i can't forget our oxygen up here.

01:04 So phony acids synthesis is going to a occur with the addition of melonal co -a.

01:13 So acetyl -coa can be turned into melonal co -a using co2.

01:23 So we're going to add a co2, and this is actually going to take atp as well.

01:28 And this is the rate -determining step of fatty acid synthesis, and it uses the enzyme acetylcoa carboxylase.

01:37 And we can just shorten that to acc.

01:40 So not super important for this question, but just some good things to know.

01:44 So now we are going to have malonal coa, which has our isotope labeled carbon, and we've popped off one of the hydrogens to add our co2, say c -o -o -m minus.

02:10 That's representing our cr2.

02:12 And then again, we have our just drawing it out a little different here...

Please give Ace some feedback