Hello you guys,

 

I was just reading about lipids synthesis, triacylglycerol and phospholipids to be more exact, and there's a thing that confuses me a bit.

We all now that triacylglycerol is stored in the adipose tissue and broken down, after which free fatty acids can enter the blood. Now to quote Stryer 7th ed. it is said that

"The liver is the primary stie of triacylglycerol synthesis (okay!). (But but..) From the liver, the triacylglycerol are transported to the muscle for energy conversion (beta-oxidation that would be?) or to the adipose cells for storage"

 

My question is now, why the heck would the liver produce triacylglycerol for the muscle, if the the muscle could've just taken up the free fatty acids in the first place and used them for energy conversion? That is why go from Adipose -> Liver -> muscle and not just Adipose -> muscle?

 

I hope my question isn't too stupid, but we have upcoming exams and I really wanna get it all right!

 

Thanks in advance

Edited December 23, 201213 yr by mntsh

I am not an expert, but I have some ideas that could be explored. Dietary lipids (including fatty acids) might be packaged into chylomicrons (the fatty acids would be first converted into TAGs) for consumption by other tissues. However, if the fatty acids are being synthesized from other carbon sources such as glucose, that would take place in the liver. The the liver would package them as VLDL particles.

Free fatty acids are only free from the glycerol, from what I'd assume. Triglyceride transport would have to assist in this process. Otherwise the blood would be a detergent which is a known carcinogen.

 

And that is not to say there are never free fatty acids. They are just attenuated by a more correct and proper process.

Edited February 2, 201312 yr by vampares

Let me clarify. When the liver produces a VLDL particle, the fatty acids are no longer free, but rather in the form of TAGs.

 

triglyceride [tri-glis´er-īd] a compound consisting of three molecules of fatty acids bound with one molecule of glycerol; a neutral fat that is the usual storage form of lipids in animals.

 

triglycerides are most likely back up fuel which circulate in the blood and are used by cells when needed.

TAG = triacylglycerol = triglyceride. I am not sure whether or not this was clear from my previous comments. The main storage location for TAGs is in droplets within adipose tissue.