Even chain FA vs Odd chain FA

[sephonly]

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So, even chain fatty acids produce Acetyl-CoA, and odd chain fatty acids produce Propionyl-CoA.

Propionyl-CoA can enter the TCA cycle as sucinyl-CoA and undergo gluconeogenesis. So why is it that the Acetyl-CoA produced by even-chain FA's can't enter the TCA cycle at the top and go on to make Citrate and also participate in Gluconeogenesis?

I'm sorry I tried looking at other sources and I don't understand this bit. I'm sure it's something silly...

 

[Phloston]

So, even chain fatty acids produce Acetyl-CoA, and odd chain fatty acids produce Propionyl-CoA.

Propionyl-CoA can enter the TCA cycle as sucinyl-CoA and undergo gluconeogenesis. So why is it that the Acetyl-CoA produced by even-chain FA's can't enter the TCA cycle at the top and go on to make Citrate and also participate in Gluconeogenesis?

I'm sorry I tried looking at other sources and I don't understand this bit. I'm sure it's something silly...

I'm not really sure what you're confused about.

With odd-chain fatty acids, the result is succinyl-CoA (as you've already mentioned), which is forced into the TCA cycle (the exception is its use alongside thiophorase, but that's not important here). With acetyl-CoA, it doesn't have to be used for the TCA cycle, but can also be used for ketone synthesis.

 

[DrTomGr]

So, even chain fatty acids produce Acetyl-CoA, and odd chain fatty acids produce Propionyl-CoA.

Propionyl-CoA can enter the TCA cycle as sucinyl-CoA and undergo gluconeogenesis. So why is it that the Acetyl-CoA produced by even-chain FA's can't enter the TCA cycle at the top and go on to make Citrate and also participate in Gluconeogenesis?

I'm sorry I tried looking at other sources and I don't understand this bit. I'm sure it's something silly...

Propionyl CoA enters the TCA circle as Succinyl CoA and follows the pathway until it forms OAA the actual substrate for Gluconeogenesis

Acetyl CoA enters the TCA circle as citrate but you can't say that it forms OAA because the carbons of Acetyl CoA are gone as CO2 as long as Succinyl CoA is formed. The rest of the reactions recycle the OAA.
So Acetyl CoA doesn't participate in Gluconeogenesis.

Don't forget thought that Aceyl CoA is really important for the process of Gluconeogenesis as it is an obligate activator of Pyruvate Carboxylase.

 

[sephonly]

Ah thanks guys. Last-week cramming, making sure not missing easy concepts from biochem (my 2nd weakest subject after anatomy)

I guess what I was confused about was why Proponyl-CoA was being singled out as being able to enter the TCA cycle (like, why wasn't Acetyl-CoA also going to OAA), but its actually highlighting the fact that its only Acetyl-CoA that can be turned into ketone bodies.