Reactants and Products of Lipid Catabolism - Biochemistry

One round of beta oxidation of fatty acids removes 2 carbons off the fatty acid chain at a time, yielding acetyl-CoA as well as and (from the 2 oxidation steps). ATP is not a direct product of beta oxidation, however the acetyl-CoA and reduced coenzymes will provide ATP via Krebs cycle and electron transport.

-oxidation of fatty acids yields large quantities of acetyl-CoA, all of which enters the citric acid cycle. The only intermediate in the citric acid cycle that can form back into glucose is oxaloacetate. It can be turned into phosphoenolpyruvate via phosphoenolpyruvate carboxykinase.

In the first step of beta oxidation the enzyme acyl-CoA dehydrogenase forms a trans-double bond between the two carbons at the site that will eventually be cleaved.

First, one must know what the products of one cycle of the beta oxidation pathway are. Each cycle yields , , 1 acetyl-CoA, and a fatty acyl-CoA molecule 2 carbons shorter than the original.

Therefore, an eighteen-carbon fatty acyl-CoA input can go through the beta oxidation cycle 8 times (the last round only a 2 carbon acetyl CoA remains, which cannot enter the beta oxidation pathway again). That means there are molecules, 9 acetyl-CoA molecules, and molecules that can be generated from an eighteen-carbon fatty acyl-CoA.

It may be confusing to understand why there are only and molecules and 9 acetyl-CoA, but if one is solving a problem such as this for the first time, go through and draw out the products following each round of the beta oxidation cycle.

2.5 ATP on average can be formed from each molecule, and 1.5 ATP from each molecule through the electron transport chain. 10 ATP can be formed in total from one acetyl-CoA entering into the Krebs cycle (by the products of and ), along with one GTP molecule.

Therefore:

If taken into consideration, 2 ATP are needed to activate a fatty acid and allow it to enter into the mitochondria via the enzyme acyl-CoA synthetase.

Therefore, the toTal net yield is

For a quick reference, the following equations can be used:

Where is number of carbons of aneven numbered fatty acid chain.

For each round of beta-oxidation, two carbon atoms are removed from the fatty acid chain. These two carbon atoms come off of the chain in the form of acetyl-CoA. Additionally, high energy electron carriers in the form of NADH and are also produced, thus making beta-oxidation a process that liberates a great deal of energy.

Since the fatty acid that we're starting with has a total of carbon atoms, we can expect there to be a total of acetyl-CoA molecules produced, since each of these contains two carbons from the fatty acid.

During beta oxidation of fatty acids, carbons are removed from the fatty acid chain two at a time. So when a fatty acid is composed of an even number of carbons (as most are) 4 carbons will be left at the end. This will be cleaved into two separate 2 carbon molecules - two acetyl-CoA molecules.

During beta-oxidation of fatty acids, carbons are removed from the fatty acid chain two at a time. So when a fatty acid is composed of an odd number of carbons, 5 carbons will be left at the end. This will be cleaved into two separate molecules - one with 3 carbons and one with 2 carbons. This is one acetyl-CoA molecule (2 carbons) and one propionyl-CoA molecule (3 carbons).

Fatty acids with an odd number of carbons are more common in plants and marine organisms than they are in mammals. When humans consume these organisms in their diets, they must metabolize them through beta oxidation. The end product of this reaction is propionyl-CoA rather than acetyl-CoA, which is formed during cleavage of two-carbon segments (fatty acids with an even number of carbons). Before entering the Krebs cycle, the propionyl-CoA must be transformed into succinyl-CoA.

Each round of beta oxidation yields one molecule of acetyl-CoA (along with one molecule of FADH2 and one molecule of NADH). Both electron carriers feed into the electron transport chain, ultimately yielding ATP via chemiosmosis. Since the organic product of beta oxidation (acetyl-CoA) contains two carbons, nine rounds of beta oxidation are required to fully oxidize a fatty acid with a 20-carbon hydrocarbon tail. Recognize that it is NOT 10 rounds because the last round (9th) will cut the now 4-carbon hydrocarbon tail, yielding two acetyl-CoA molecules. As a rule, a fatty acid with a hydrocarbon tail of of carbons undergoes rounds of beta oxidation to be full oxidized.

Overall, for a fatty acid with 20 carbons in its hydrocarbon chain, 9 rounds of beta oxidation yielding 10 molecules of acetyl-CoA constitutes complete oxidation.

One round of beta oxidation of fatty acids removes 2 carbons off the fatty acid chain at a time, yielding acetyl-CoA as well as and (from the 2 oxidation steps). ATP is not a direct product of beta oxidation, however the acetyl-CoA and reduced coenzymes will provide ATP via Krebs cycle and electron transport.

-oxidation of fatty acids yields large quantities of acetyl-CoA, all of which enters the citric acid cycle. The only intermediate in the citric acid cycle that can form back into glucose is oxaloacetate. It can be turned into phosphoenolpyruvate via phosphoenolpyruvate carboxykinase.

In the first step of beta oxidation the enzyme acyl-CoA dehydrogenase forms a trans-double bond between the two carbons at the site that will eventually be cleaved.

First, one must know what the products of one cycle of the beta oxidation pathway are. Each cycle yields , , 1 acetyl-CoA, and a fatty acyl-CoA molecule 2 carbons shorter than the original.

Therefore, an eighteen-carbon fatty acyl-CoA input can go through the beta oxidation cycle 8 times (the last round only a 2 carbon acetyl CoA remains, which cannot enter the beta oxidation pathway again). That means there are molecules, 9 acetyl-CoA molecules, and molecules that can be generated from an eighteen-carbon fatty acyl-CoA.

It may be confusing to understand why there are only and molecules and 9 acetyl-CoA, but if one is solving a problem such as this for the first time, go through and draw out the products following each round of the beta oxidation cycle.

2.5 ATP on average can be formed from each molecule, and 1.5 ATP from each molecule through the electron transport chain. 10 ATP can be formed in total from one acetyl-CoA entering into the Krebs cycle (by the products of and ), along with one GTP molecule.

Therefore:

If taken into consideration, 2 ATP are needed to activate a fatty acid and allow it to enter into the mitochondria via the enzyme acyl-CoA synthetase.

Therefore, the toTal net yield is

For a quick reference, the following equations can be used:

Where is number of carbons of aneven numbered fatty acid chain.

For each round of beta-oxidation, two carbon atoms are removed from the fatty acid chain. These two carbon atoms come off of the chain in the form of acetyl-CoA. Additionally, high energy electron carriers in the form of NADH and are also produced, thus making beta-oxidation a process that liberates a great deal of energy.

Since the fatty acid that we're starting with has a total of carbon atoms, we can expect there to be a total of acetyl-CoA molecules produced, since each of these contains two carbons from the fatty acid.

During beta oxidation of fatty acids, carbons are removed from the fatty acid chain two at a time. So when a fatty acid is composed of an even number of carbons (as most are) 4 carbons will be left at the end. This will be cleaved into two separate 2 carbon molecules - two acetyl-CoA molecules.

During beta-oxidation of fatty acids, carbons are removed from the fatty acid chain two at a time. So when a fatty acid is composed of an odd number of carbons, 5 carbons will be left at the end. This will be cleaved into two separate molecules - one with 3 carbons and one with 2 carbons. This is one acetyl-CoA molecule (2 carbons) and one propionyl-CoA molecule (3 carbons).

Fatty acids with an odd number of carbons are more common in plants and marine organisms than they are in mammals. When humans consume these organisms in their diets, they must metabolize them through beta oxidation. The end product of this reaction is propionyl-CoA rather than acetyl-CoA, which is formed during cleavage of two-carbon segments (fatty acids with an even number of carbons). Before entering the Krebs cycle, the propionyl-CoA must be transformed into succinyl-CoA.

Each round of beta oxidation yields one molecule of acetyl-CoA (along with one molecule of FADH2 and one molecule of NADH). Both electron carriers feed into the electron transport chain, ultimately yielding ATP via chemiosmosis. Since the organic product of beta oxidation (acetyl-CoA) contains two carbons, nine rounds of beta oxidation are required to fully oxidize a fatty acid with a 20-carbon hydrocarbon tail. Recognize that it is NOT 10 rounds because the last round (9th) will cut the now 4-carbon hydrocarbon tail, yielding two acetyl-CoA molecules. As a rule, a fatty acid with a hydrocarbon tail of of carbons undergoes rounds of beta oxidation to be full oxidized.

Overall, for a fatty acid with 20 carbons in its hydrocarbon chain, 9 rounds of beta oxidation yielding 10 molecules of acetyl-CoA constitutes complete oxidation.

One round of beta oxidation of fatty acids removes 2 carbons off the fatty acid chain at a time, yielding acetyl-CoA as well as and (from the 2 oxidation steps). ATP is not a direct product of beta oxidation, however the acetyl-CoA and reduced coenzymes will provide ATP via Krebs cycle and electron transport.