Energy from fatty acids?

[abiran]

These questions are confusing me?can u please help:
1)I don't understand why fatty acids have 2.5 times the energy as carbohydrates or proteins?
2) do saturated fatty acids have more energy than carbo/proteins or unsaturated fatty acids than carb/prot?

3)I know that saturated fatty acids contain more energy than unsaturated but why though?is it because of they have more London dispersion forces?

thnx alot..a answer to at least one question is greatly appreciated.

[mith]

london disperson forces are in all molecules, plus they're tiny so that's not the answer.

[JackBean]

It's all about the oxidation state of all atoms (the more reduced, the more energy you can gain;) + in 1) FA are hydrophobic, while polysaccharides are hydrophilic and bind about 2-times their weight of water

[abiran]

THnx
So the anount of energy has nothing to do with if it saturated (or) unsaturated?

[JackBean]

Sure it does. The saturation of fatty acids tells you the oxidation state of the carbons

[kolean]

Fatty acids give more energy because they provide ATP by a different pathway (beta oxidation), than say carbohydrates (glycolysis)and protein (proteolysis).

Read the wikipedia article towards the end. It will even tell you why it is harder for the beta oxidation pathway for saturated, unsaturated, and even/odd number fatty acids. And towards the end it will show you the energy conversions. It mostly is about the different enzymes that are used for this specific pathway.

http://en.wikipedia.org/wiki/%CE%92-oxidation

[abiran]

Thanks alot guys...that was really helpful..the wikipedia article..

[JackBean]

Fatty acids give more energy because they provide ATP by a different pathway (beta oxidation), than say carbohydrates (glycolysis)and protein (proteolysis).

Read the wikipedia article towards the end. It will even tell you why it is harder for the beta oxidation pathway for saturated, unsaturated, and even/odd number fatty acids. And towards the end it will show you the energy conversions. It mostly is about the different enzymes that are used for this specific pathway.

http://en.wikipedia.org/wiki/%CE%92-oxidation

The pathway doesn't matter so much, if you had some hydroxyfatty acid with similar oxidation state as Glc, than you would gain similar amount of energy as from Glc, because you just couldn't get more.

[kolean]

It seems to me that the pathway does matter in a Biological System. It is all about how many phosphates you can take from one substrate to the next, which utilizes specific enzymes, and produces the main energy substrate, ATP.

[JackBean]

OK, that can matter, but the thermodynamics laws tell you, that you get always the same energy when going from one substance (read oxidation state) to another, no matter of path.
IMHO, nature is so perfect, it gets every piece of energy, whenever it can and save it in some way. Of course, there is probably some difference in efficiency of both pathways, but I think, it won't be much significant Anyway, that can be easily calculated Of course, that will be influenced by localisation of all parts of the pathways etc.

[kolean]

Well, most biological systems are not efficient. That is why most give off energy in the form of heat. Though, true it is all a form of energy, but when dealing with biological systems, energy efficiency to get the most energy just for processing the organism's metabolism, is not the case.
And a pathway will only go if there is a specific enzyme to catalyze the reaction of a step in the pathway. As is seen when people try to modify the fats they do eat into fats that the body doesn't recognize and they proceed thru the GI tract unhindered (which is the theory of Alli and other fat blockers for weight loss). Thus the oxidation of that fat doesn't count because it will not produce any energy for the biological system.
Which in the case of the post for saturated fats and unsaturated fats, will produce different energy for the biological system because of the different enzymes that recognize the substrates of the fatty acids. Like a trans bond and a cis bond (of an unsaturated fatty acid) make the difference in substrate recognition (and thus a different pathway), as it produces a non-kink and a kink, respectively, in the structure of the fatty acid.

Thermodynamics in a lab is just so wonderfully easy. Sigh, the good ole days (as a chemical engineering major). Biological systems are just so complicated, but very challenging to figure out.