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Why is there a difference in available energy in saturated vs. unsaturated fatty acids?
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Krishna
Why is there a difference in available energy in saturated vs. unsaturated fatty acids?
Yes, it is a fact that saturated fats contain more gross energy due to higher H+ concentration. However, unsaturated fats are more digestible and have higher absorption rate, and therefore the metabolizable energy that unsaturated fats provide is higher than that provided by saturated fats.
Yes, it is a fact that saturated fats contain more gross energy due to higher H+ concentration. However, unsaturated fats are more digestible and have higher absorption rate, and therefore the metabolizable energy that unsaturated fats provide is higher than that provided by saturated fats.
The total energy stored in macromolecules is commonly quantified by the amount of $\ce{ATP}$ produced, as $\ce{ATP}$ is used throughout the body to couple reactions and make them thermodynamically favorable.
First, as the oxidation of a double bond in an fully saturated fatty acid requires a reducing agent, you here produce $\ce{FADH2}$ from $\ce{FAD+}$ which is equivalent to a $\ce{1.5 ATP}$ gain.[1]
Also, unsaturated fat has double bonds in cis positions that are unfavorable to beta oxidation.[2] An enzyme coupled reaction is needed for the double bond shift. Therefore, an enzyme coupled reaction that requires energy (in the reductant form $\ce{NADPH}$) is needed to make the molecule a trans fat with a shift in bond position in order to continue oxidizing the molecule completely. $\ce{NADPH}$, usually is defined as $\ce{2.5ATP}$ equivalents[1] and this extra energy expenditure in shifting the double bond is why less energy is ultimately produced. Note, this $\ce{NADPH}$ is only used when unsaturated fats have an even numbered bond position.[2] This happens with polyunsaturated fats when the first bond is shifted.
For example:
18:2 linoleic acid will yield $1.5 + 1.5 + 2.5 = 5.5$ less $\ce{ATP}$ than 18:0 stearic acid.
The total energy stored in macromolecules is commonly quantified by the amount of $\ce{ATP}$ produced, as $\ce{ATP}$ is used throughout the body to couple reactions and make them thermodynamically favorable.
First, as the oxidation of a double bond in an fully saturated fatty acid requires a reducing agent, you here produce $\ce{FADH2}$ from $\ce{FAD+}$ which is equivalent to a $\ce{1.5 ATP}$ gain.[1]
Also, unsaturated fat has double bonds in cis positions that are unfavorable to beta oxidation.[2] An enzyme coupled reaction is needed for the double bond shift. Therefore, an enzyme coupled reaction that requires energy (in the reductant form $\ce{NADPH}$) is needed to make the molecule a trans fat with a shift in bond position in order to continue oxidizing the molecule completely. $\ce{NADPH}$, usually is defined as $\ce{2.5ATP}$ equivalents[1] and this extra energy expenditure in shifting the double bond is why less energy is ultimately produced. Note, this $\ce{NADPH}$ is only used when unsaturated fats have an even numbered bond position.[2] This happens with polyunsaturated fats when the first bond is shifted.
For example:
18:2 linoleic acid will yield $1.5 + 1.5 + 2.5 = 5.5$ less $\ce{ATP}$ than 18:0 stearic acid.
Yes, it is a fact that saturated fats contain more gross energy due to higher H+ concentration. However, unsaturated fats are more digestible and have higher absorption rate, and therefore the metabolizable energy that unsaturated fats provide is higher than that provided by saturated fats.
Yes, it is a fact that saturated fats contain more gross energy due to higher H+ concentration. However, unsaturated fats are more digestible and have higher absorption rate, and therefore the metabolizable energy that unsaturated fats provide is higher than that provided by saturated fats.
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The total energy stored in macromolecules is commonly quantified by the amount of $\ce{ATP}$ produced, as $\ce{ATP}$ is used throughout the body to couple reactions and make them thermodynamically favorable.
First, as the oxidation of a double bond in an fully saturated fatty acid requires a reducing agent, you here produce $\ce{FADH2}$ from $\ce{FAD+}$ which is equivalent to a $\ce{1.5 ATP}$ gain.[1]
Also, unsaturated fat has double bonds in cis positions that are unfavorable to beta oxidation.[2] An enzyme coupled reaction is needed for the double bond shift. Therefore, an enzyme coupled reaction that requires energy (in the reductant form $\ce{NADPH}$) is needed to make the molecule a trans fat with a shift in bond position in order to continue oxidizing the molecule completely. $\ce{NADPH}$, usually is defined as $\ce{2.5ATP}$ equivalents[1] and this extra energy expenditure in shifting the double bond is why less energy is ultimately produced. Note, this $\ce{NADPH}$ is only used when unsaturated fats have an even numbered bond position.[2] This happens with polyunsaturated fats when the first bond is shifted.
For example:
18:2 linoleic acid will yield $1.5 + 1.5 + 2.5 = 5.5$ less $\ce{ATP}$ than 18:0 stearic acid.
References:
[1]: http://www.saylor.org/site/wp-content/uploads/2013/04/BIO101A-6.2.3-CellularRespiration.pdf
[2]: https://en.wikipedia.org/wiki/Beta_oxidation
The total energy stored in macromolecules is commonly quantified by the amount of $\ce{ATP}$ produced, as $\ce{ATP}$ is used throughout the body to couple reactions and make them thermodynamically favorable.
First, as the oxidation of a double bond in an fully saturated fatty acid requires a reducing agent, you here produce $\ce{FADH2}$ from $\ce{FAD+}$ which is equivalent to a $\ce{1.5 ATP}$ gain.[1]
Also, unsaturated fat has double bonds in cis positions that are unfavorable to beta oxidation.[2] An enzyme coupled reaction is needed for the double bond shift. Therefore, an enzyme coupled reaction that requires energy (in the reductant form $\ce{NADPH}$) is needed to make the molecule a trans fat with a shift in bond position in order to continue oxidizing the molecule completely. $\ce{NADPH}$, usually is defined as $\ce{2.5ATP}$ equivalents[1] and this extra energy expenditure in shifting the double bond is why less energy is ultimately produced. Note, this $\ce{NADPH}$ is only used when unsaturated fats have an even numbered bond position.[2] This happens with polyunsaturated fats when the first bond is shifted.
For example:
18:2 linoleic acid will yield $1.5 + 1.5 + 2.5 = 5.5$ less $\ce{ATP}$ than 18:0 stearic acid.
References:
[1]: http://www.saylor.org/site/wp-content/uploads/2013/04/BIO101A-6.2.3-CellularRespiration.pdf
[2]: https://en.wikipedia.org/wiki/Beta_oxidation
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