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Oh my god, this has confused me for months and I finally think I get it, so I hope I can explain it decently. When fatty acids are oxidized, the acetyl-CoA can enter the Krebs cycle, and one would think that the oxaloacetate generated by the Krebs cycle could be converted to acetyl-CoA, which could then be converted to pyruvate for gluconeogenesis. This can't happen, though, because even though oxaloacetate is made, there is no net increase in oxaloacetate (two carbons are lost in the Krebs cycle for every two in the acetyl-CoA coming in). Oxaloacetate can't be taken out of the cycle, then, because then the cycle would be depleted and the only way to replenish it is through one of the anapleoritic reactions, which involve products of glycolysis (PEP and pyruvate). If there is enough PEP or pyruvate around to replenish the oxaloacetate you're taking out to make glucose, chances are you don't need to make glucose in the first place. Pyruvate from glucose or amino acids can be used to make sugars before it is converted to acetyl-CoA, but the pyruvate dehydrogenase complex reaction is irreversible, so once pyruvate is made into acetyl-CoA it cannot be used to make glucose; it is committed to either fatty acid synthesis or the Krebs cycle. Plants can make glucose from fatty acids, but this is only because they are able to use the glyoxlyate cycle instead of the Krebs cycle. The glyoxylate cycle bypasses the step in the Krebs cycle (the alpha-ketoglutarate dehydrogenase step) in which the two carbons are lost as CO2, so when plant acetyl-CoA enters the glyoxylate cycle there IS a net increase in oxaloacetate which can be used to make pyruvate.
Wiki User
∙ 15y ago
Wiki User
∙ 11y agoDuring exercise of fasting, the glucose intake is not sufficient to meed the needs of glucose requiring tissue such as the brain. So, the body must find a way to synthesise glucose from substrates which are available in the body. It would be better if the pyruvate --> glucose reaction was reversible (as it is in plants and so acetyl CoA could be used as a substrate, meaning that through the beta oxidation pathway of fats, fatty acids could be used to generate glucose) but it is not, so gluconeogenesis cannot use acetyl CoA as a subtrate, instead using oxaloacetate from the Kreb's cycle.
It would have been evolutionary beneficial to produce an enzyme which can do the reaction acetyl CoA --> pyruvate ....-->....--> glucose but humans do not have it.
Wiki User
∙ 11y agoEnergy is neither created nor destroyed in ordinary chemical reactions. The energy comes from making and breaking chemical bonds. As glucose goes through glycolysis and onto the TCA cycle, chemical bonds are made and broken thus releasing energy.
Wiki User
∙ 9y agothere is no need for it! because glucose is widely available to the body from diet and the lysis of polysaccharides, to metabolize glucose, our system converts it to pyruvic acid and then acety coA etc...ultimately to earn energy!
There is no enzyme to catalyze such reaction to convert acetyl coA to pyruvate, and it wont be advantageous to our body in anyway.
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What are fatty acids converted to in Beta-oxidation?
Acetyl CoA
Can long-chain fatty acids be absorbed directly into the blood?
no
Glucose molecules are to starch as what are to lipids?
This is an analogy between the molecular components of two different macromolecules. Glucose molecules compose starch, and its correspondent to proteins would be amino acids to solve this question.
Which muscle cells break down glucose to generate ATP under oxygen deficient conditions they will form?
lactid acid, glycogen, glucose, fatty acids
What are the monomers of triglyceride?
1 glycerol and 3 fatty acids so the monomers basically are glycerol and fatty acids
Which of the following compounds cannot be converted to glucose?
Fatty Acids.
Approximately what percentage of triglycerides CANNOT be converted to glucose?
triglycerides consist of 3 fatty acids and glycerol. because fatty acids break down to acetyl CoA they cannot be made into glucose. the glycerol portion of a triglyceride can be converted to pyruvate and thus yield glucose. and glycerol is about 5% of a triglyceride molecule. So the answer is 95% of a triglyceride (fatty acid) cannot be converted to glucose.
Where does glucose go when it leaves the small intestine?
After leaving the gut, the liver is the first tissue to use dietary glucose. In the liver, glucose can be converted to glycogen to be stored or distributed through out the body for energy. It can also be converted to fatty acids. The conversion of glucose to fatty acids usually only happens if energy intake has exceeds energy expenditure.
When needed for a source of energy fatty acids are broken down in glucose?
fat is broken down into fatty acids
What part of a fat molecule CAN be used to make glucose?
The part of a fat molecule that can be used to make glucose is the fatty acids. The daily lipid intake can be produced from fatty acids.
What is the common pathway for oxidation of products of glucose and fatty acids catabolism?
The common pathway for oxidation of products of glucose and fatty acids catabolism is referred to as the b-oxidation pathway.
What are fatty acids converted to in Beta-oxidation?
Acetyl CoA
Can fatty acids be converted to oxaloacetate?
Not directly. Fatty acid β-oxidation results in acetyl CoA, which is then entered to the Citric Acid cycle. The "last" step of the cycle is the formation of oxaloacetate from malate.
Nutrients normally found in plasma?
Glucose amino acids and fatty acids can be metabolized within the cell to liberate?
CO2 CO2
What are the four basic units derived from food?
glucose, amino acids, glycerol, fatty acids.
Can you convert fat to glucose?
yes in fasted states (or when you have used your glycogen stores), glucagon or adrenaline can breakdown stored triglycerides (in adipose tissue) into glycerol and fatty acids. The glycerol goes to the liver when it is involved in gluconeogenesis (synthesis of glucose from non-carb source). This is essentially a reversal of glycolysis: The glycerol molecule is converted to dihydroxyacetone phosphate, which then is converted to fructose 1,6 biphosphate and then after a number of steps, is converted to glucose. I dont think the glycerol molecule is converted to pyruvate, but instead joins in the pathway at the step decribed above.
