[NeginMeshkati]

Consider a preparation that contains all the enzymes and cofactors necessary for the biosynthesis of palmitate from
added acetyl-CoA and malonyl-CoA.



(a) If [2-14C-2-3H]acetyl-CoA (see the left figure above) and an excess of unlabeled malonyl-CoA are added as substrates, how many 3H atoms are incorporated into every molecule of palmitate, and what are their locations? How many 14C atoms are incorporated and what are their locations? (b) If unlabeled acetyl-CoA and an excess of [1,3-14C-2-3H]malonyl-CoA (see the right figure above) are added as substrates, how many 3H atoms are incorporated into every molecule of palmitate, and what are their locations? How many 14C atoms are incorporated and what are their locations? (c) Suppose that both of the labeled molecules above were added as substrates, how many 3H atoms are incorporated into every molecule of palmitate, and what are their locations? How many 14C atoms are incorporated and what are their locations?

[Babcock_Hall]

Welcome to the forum.  It is a forum rule that you must show your attempt before we can help you.  A good place to start might be for you to show some of the appropriate reactions.

[NeginMeshkati]

Thank you for letting me know. I wrote down the general Biosynthesis of a Fatty Acid. I attached the file, I just do not understand how I am supposed to find out the location of the H3- atoms.

[Babcock_Hall]

It might be easier to start with carbon.  What happens to the free carboxylate group of malonyl CoA when it condenses with acetyl CoA?  What is its fate, in other words?  You are missing a side product in your scheme.

With respect to tritium, again, I suggest looking at the fate of the atoms, but you will need to think about the chemical mechanism by which acetyl CoA attacks malonyl CoA.  How does acetyl CoA become sufficiently nucleophilic to do so.