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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.
Fatty acids cannot be converted directly to glucose because they undergo beta-oxidation in the mitochondria to produce acetyl-CoA, which cannot be used as a substrate for gluconeogenesis in the cytoplasm. Acetyl-CoA is a two-carbon molecule and cannot be converted into pyruvate, which is a key intermediate in the gluconeogenic pathway. Therefore, fatty acids are not a direct precursor for glucose synthesis.
During 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.
Energy 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.
there 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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Into what body fluids do glucose fatty acids amino acids pass?
Glucose, fatty acids, and amino acids pass into the bloodstream.
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.
What are the final end products for carbohydrates lipids and proteins?
Carbohydrates: Glucose Lipids: Fatty acids and glycerol Proteins: Amino acids
What are fatty acids converted to in Beta-oxidation?
Fatty acids are converted into acetyl-CoA molecules during beta-oxidation. Acetyl-CoA is a crucial molecule in the citric acid cycle (Krebs cycle) which generates energy through the production of ATP.
Can long-chain fatty acids be absorbed directly into the blood?
No, long-chain fatty acids are broken down into smaller molecules called monoglycerides and free fatty acids in the small intestine before they can be absorbed into the bloodstream. They are then reassembled into triglycerides and packaged into chylomicrons for transport.
Which of the following compounds cannot be converted to glucose?
Fatty Acids.
Into what body fluids do glucose fatty acids amino acids pass?
Glucose, fatty acids, and amino acids pass into the bloodstream.
Approximately what percentage of triglycerides CANNOT be converted to glucose?
Approximately 10-15% of triglycerides cannot be converted to glucose. These triglycerides are primarily stored in adipose tissue and are used for energy production through beta-oxidation in the liver, rather than being converted to glucose.
What cannot be used to form new glucose in the body?
Fatty acids cannot be used to form new glucose in the body because they are molecules made up of carbon and hydrogen, which cannot be converted to glucose through the process of gluconeogenesis. Instead, fatty acids are broken down through beta-oxidation to produce energy in the form of ATP.
When needed for a source of energy fatty acids are broken down in glucose?
fat is broken down into fatty acids
What is the end product of fat and oil?
The end products of fat digestion are fatty acids and glycerol.
Where does glucose go when it leaves the small intestine?
Glucose is absorbed into the bloodstream from the small intestine. It is then transported to cells throughout the body to be used as a source of energy. Some of the glucose may also be stored in the liver and muscles for later use.
Are fatty acids sub-units of carbohydrates?
No, fatty acids are not sub-units of carbohydrates. Fatty acids are components of lipids, while carbohydrates are composed of sugar molecules like glucose.
Can fatty acids and glycerol be used as sources of energy?
Yes, fatty acids and glycerol can be used as sources of energy in the body. Fatty acids can be broken down through beta-oxidation to generate ATP, providing a long-term energy source. Glycerol, after being converted to glucose via gluconeogenesis, can also be used for energy production.
When amino acids are deaminated what source can they be used as?
When amino acids are deaminated, the resulting carbon skeletons can be used as energy sources through processes like glycolysis or the citric acid cycle. They can also be converted into glucose, fatty acids, or ketone bodies for energy production or storage.
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.
What does not serve as a source of acids in the body?
Fats do not serve as a source of acids in the body. Instead, they are broken down into fatty acids and glycerol for energy production, and are not directly involved in acid-base balance.
