Reduction of Fatty Acids

[MedGrl@2022]

Hi everyone. This might be a silly question but I need to ask it to make sure I know what is going on. My EK book says "Fatty acids are highly reduced, which allows them to store more than twice the energy (about 9 kcal/gram) of carbohydrates or proteins (about 4 kcal/gram)."

In what sense does it mean that fatty acids are "reduced"? Like redox reaction, addition of hydrogens...

Thank you once again for all your help.

Verónica

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[Postictal Raiden]

Hi everyone. This might be a silly question but I need to ask it to make sure I know what is going on. My EK book says "Fatty acids are highly reduced, which allows them to store more than twice the energy (about 9 kcal/gram) of carbohydrates or proteins (about 4 kcal/gram)."

In what sense does it mean that fatty acids are "reduced"? Like redox reaction, addition of hydrogens...

Thank you once again for all your help.

Verónica

Reduced means possessing more electrons. Remember, electrons are the driving force of the ETC, which eventually produces ATP. Electrons (energy) is stored in the C-H bond of the alkyl chain of the fatty acid. Compare a fatty acid chain to glucose, for example. You'll find that glucose is much more oxidized than the Fatty acid. Each single carbon is bonded to an oxygen, even on carbon is double bonded to oxygen; while the alkyl chain of the fatty acid is free of oxygen (except for the carboxylic acid end of the chain).

 

[MedGrl@2022]

Reduced means possessing more electrons. Remember, electrons are the driving force of the ETC, which eventually produces ATP. Electrons (energy) is stored in the C-H bond of the alkyl chain of the fatty acid. Compare a fatty acid chain to glucose, for example. You'll find that glucose is much more oxidized than the Fatty acid. Each single carbon is bonded to an oxygen, even on carbon is double bonded to oxygen; while the alkyl chain of the fatty acid is free of oxygen (except for the carboxylic acid end of the chain).

Wow thanks! That makes sense! Also fatty acids are essentially long CH chains with COOH at the end which allows them to store more energy per gram when compared to carbohydrates or proteins, right?

Is it the electrons which are stored in the C-H bond that produce the NADH, FADH2 and acetyl coA which also contribute to fatty acids producing more energy? This seems to be the major difference with glucose because glucose goes through glycolysis to produce 2 pyruvate which then produces an NADH each. However, glycolysis also produces a net 2 ATP, 2 NADH.

However, is it the fact that fatty acids are longer and since 2 carbons make up acetyl coA therefore more NADH, FADH2 and acetyl coA are produced when compared to the ATPs and NADH of glycolysis?

Also, the reason that proteins only produce about 4 kcal/gram is because they are deaminated and need to undergo chemical conversions (which probably uses up energy) and enters the glycolysis or the Kreb cycle at various stages depending on the amino acid (or fat for storage)?

I just want to make sure that I understand all of this. Thank you for your help.

Also, why isn't the C-O bond useful for energy storage? Is it because O is very electronegative and will "take/absorb" the electron?

Thank you once again for all your help.

Best,

Verónica

 

[MedGrl@2022]

Wow thanks! That makes sense! Also fatty acids are essentially long CH chains with COOH at the end which allows them to store more energy per gram when compared to carbohydrates or proteins, right?

Is it the electrons which are stored in the C-H bond that produce the NADH, FADH2 and acetyl coA which also contribute to fatty acids producing more energy? This seems to be the major difference with glucose because glucose goes through glycolysis to produce 2 pyruvate which then produces an NADH each. However, glycolysis also produces a net 2 ATP, 2 NADH.

However, is it the fact that fatty acids are longer and since 2 carbons make up acetyl coA therefore more NADH, FADH2 and acetyl coA are produced when compared to the ATPs and NADH of glycolysis?

Also, the reason that proteins only produce about 4 kcal/gram is because they are deaminated and need to undergo chemical conversions (which probably uses up energy) and enters the glycolysis or the Kreb cycle at various stages depending on the amino acid (or fat for storage)?

I just want to make sure that I understand all of this. Thank you for your help.

Also, why isn't the C-O bond useful for energy storage? Is it because O is very electronegative and will "take/absorb" the electron?

Thank you once again for all your help.

Best,

Verónica

Anyone have any insight into my questions above or am I completely wrong... ?!

Thank you for all your help.

Sincerely,

Verónica

 

[Endure]

I only skimmed your question briefly, so I apologize if I'm repeating what's already been said.

Wow thanks! That makes sense! Also fatty acids are essentially long CH chains with COOH at the end which allows them to store more energy per gram when compared to carbohydrates or proteins, right?

Is it the electrons which are stored in the C-H bond that produce the NADH, FADH2 and acetyl coA which also contribute to fatty acids producing more energy? This seems to be the major difference with glucose because glucose goes through glycolysis to produce 2 pyruvate which then produces an NADH each. However, glycolysis also produces a net 2 ATP, 2 NADH.

What is principally responsible for the high energy yield of fatty acids is the extended hydrocarbon chain, which is capable of producing several-fold greater acetyl CoA molecules than glucose.

If you're interested, you should look at the complete pathway for fatty acid metabolism. The only way I intuitively understand the big picture is if I understand what happens in the small picture. Each time a two carbon fragment from a fatty acid chain is oxidized, NAD and FAD are reduced. This contributes to the energy generated at the conclusion of the pathway during oxidative phosphorylation. Glycolysis involves the reduction of NAD and FAD as well, only to a much lesser degree than in beta-oxidation.

However, is it the fact that fatty acids are longer and since 2 carbons make up acetyl coA therefore more NADH, FADH2 and acetyl coA are produced when compared to the ATPs and NADH of glycolysis?

Correct. The hydrocarbon chain of fatty acids undergoes beta-oxidation to form acetyl-CoA fragments. These fragments can then enter the TCA cycle, reduce FAD and NAD and generate ATP. The reason why this produces more energy is because each C-C bond present in the hydrocarbon chain of the fatty acid can be used to produce acetyl CoA, whereas each molecule of glucose only yields two acetyl CoA.