| Course | NS230 Macronutrient Metabolism |
|---|---|
| Unit | Unit 2 |
| Paper type | Macronutrient fate summary |
| Length | About 1,140 words, 7 pages double-spaced |
| Format | APA 7 student paper |
| School | Purdue University Global |
| Program | BS in Nutrition Science |
| Updated | October 2026 |
Free sample paper for NS230 Unit 2
Three Fuels, Short Lists of Destinations: A Unit 2 Macronutrient Fate Summary That Marks the Routes the Body Lacks
[Student Name]
Purdue University Global
NS230: Macronutrient Metabolism
Unit 2 Macronutrient Fate Summary
[Instructor Name]
[Date]
The summary describes human metabolism from the sources cited; no case data are used.
Why Fates Matter
Every absorbed fuel has three broad possible fates: it can be oxidized for energy, stored or converted into something else. Which happens depends on the tissue, the hormonal state and whether the body has an enzyme route for the conversion at all. Some conversions are impossible in humans, and knowing them explains a good deal of nutrition: why fat cannot replace carbohydrate for the brain during a short fast, why protein must be broken down when glucose runs short, and why even-chain fatty acids never become glucose.
Glucose
First stop: the liver, through the portal vein. The liver traps glucose as glucose-6-phosphate and, when insulin is high, stores much of it as glycogen. The liver can hold roughly 100 grams of glycogen in a well-fed adult.
Other destinations: glucose that passes the liver reaches muscle, which stores it as glycogen, up to several hundred grams in total across the body's muscle, and oxidizes it during activity. The brain uses about 120 grams of glucose a day. Red blood cells, which lack mitochondria, depend entirely on glucose and convert it to lactate.
Conversions available: glucose can become fat through de novo lipogenesis in the liver and adipose tissue, though in humans on ordinary diets this route carries modest amounts (Hellerstein, 1999). Glucose can supply the carbon skeletons of the nonessential amino acids, such as alanine, aspartate and glutamate.
Conversions not available: glucose cannot become essential amino acids, since the body cannot make their carbon skeletons. It cannot become the essential fatty acids, linoleic and alpha-linolenic acid, because humans lack the enzymes that insert double bonds at the required positions.
Fatty Acids
First stop: dietary fat leaves the intestine in chylomicrons, enters the lymph and reaches the blood without passing the liver first. In muscle and adipose tissue, lipoprotein lipase on capillary walls releases fatty acids from the chylomicrons.
Other destinations: adipose tissue re-forms most of the fatty acids into triglyceride and stores them, which is the body's largest energy reserve. Muscle oxidizes fatty acids for energy, especially at rest and during moderate activity. Chylomicron remnants, with the remaining fat and cholesterol, go to the liver.
Conversions available: fatty acids are broken down by beta-oxidation to acetyl-CoA, which enters the citric acid cycle. When fatty acid oxidation is high and carbohydrate low, the liver converts acetyl-CoA to ketone bodies, which the brain can use after several days of fasting. The glycerol backbone of triglycerides can become glucose in the liver.
Conversions not available: even-chain fatty acids cannot become glucose. Acetyl-CoA cannot be converted back to pyruvate, because the pyruvate dehydrogenase reaction is irreversible, and the two carbons acetyl-CoA brings into the citric acid cycle are lost as carbon dioxide before oxaloacetate is regenerated. This single missing route is why fat cannot meet the brain's glucose needs in early fasting.
The most consequential gap in human metabolism is the one between acetyl-CoA and pyruvate: because that step runs one way, fatty acids can never become glucose, and every gram of glucose made during a fast must come from glycerol, lactate or amino acids instead.
Amino Acids
First stop: the liver, through the portal vein, which takes up a large share of absorbed amino acids. Branched-chain amino acids, leucine, isoleucine and valine, pass the liver largely untouched and are taken up by muscle.
Other destinations: amino acids are used to build body proteins, enzymes and other nitrogen-containing compounds. Those not needed are broken down; their amino groups are removed and their nitrogen converted to urea in the liver (Morris, 2002).
Conversions available: the carbon skeletons of glucogenic amino acids, such as alanine, can become glucose. Those of ketogenic amino acids, leucine and lysine, can become acetyl-CoA and ketone bodies, and through acetyl-CoA can contribute to fat. Several amino acids are both glucogenic and ketogenic.
Conversions not available: the body cannot store amino acids as such; there is no protein reserve comparable to glycogen or fat, so surplus amino acids must be broken down. Leucine and lysine cannot become glucose.
Where the Fates Meet
The three fuels do not run on separate tracks. Their routes converge at a few shared molecules, and those meeting points explain which conversions are possible. Glucose and glycerol meet at the three-carbon stage of glycolysis, which is why glycerol can become glucose. Glucose and several amino acids meet at pyruvate, which is why alanine can become glucose and why glucose can supply alanine's carbon. All three fuels meet at acetyl-CoA, which can enter the citric acid cycle, become fatty acids or become ketone bodies, but cannot go back to pyruvate. The citric acid cycle intermediates themselves, such as oxaloacetate and alpha-ketoglutarate, link amino acid skeletons to both energy production and glucose synthesis. Knowing these meeting points makes the list of possible and impossible conversions predictable rather than something to memorize.
Timing Across the Day
The fates also depend on timing. In the hours after a meal, with insulin high, glucose goes mainly to storage and oxidation, fatty acids to adipose storage and amino acids to protein synthesis. Overnight, with insulin low, the flows reverse: the liver releases glucose from glycogen and from gluconeogenesis, adipose tissue releases fatty acids for muscle and the liver, and some muscle protein is broken down to supply amino acids. A fate that is prominent at one time of day may be nearly absent at another, which is why a complete summary needs to say not only where a fuel can go but when it goes there.
Summary of Routes
1. Glucose to glycogen: yes. Glucose to fat: yes, modest in ordinary diets. Glucose to nonessential amino acids: yes. Glucose to essential amino acids or essential fatty acids: no.
2. Fatty acids to energy: yes. Fatty acids to ketones: yes. Even-chain fatty acids to glucose: no. Glycerol to glucose: yes.
3. Amino acids to protein: yes. Glucogenic amino acids to glucose: yes. Ketogenic amino acids to glucose: no. Amino acids stored as such: no.
How the Routes Shape Nutrition
These routes explain several practical facts. During an overnight fast, the liver keeps blood glucose steady by breaking down glycogen and making new glucose from lactate, glycerol and amino acids. In a longer fast, when liver glycogen is exhausted, gluconeogenesis supplies most glucose (Rothman et al., 1991), and the protein broken down to supply it is why prolonged fasting costs muscle. When dietary carbohydrate exceeds what glycogen can hold, conversion to fat increases (Acheson et al., 1988), but the body's first response to extra carbohydrate is to burn more of it.
References
Acheson, K. J., Schutz, Y., Bessard, T., Anantharaman, K., Flatt, J. P., & Jéquier, E. (1988). Glycogen storage capacity and de novo lipogenesis during massive carbohydrate overfeeding in man. The American Journal of Clinical Nutrition, 48(2), 240-247. https://doi.org/10.1093/ajcn/48.2.240
Hellerstein, M. K. (1999). De novo lipogenesis in humans: Metabolic and regulatory aspects. European Journal of Clinical Nutrition, 53(Suppl. 1), S53-S65. https://doi.org/10.1038/sj.ejcn.1600744
Morris, S. M., Jr. (2002). Regulation of enzymes of the urea cycle and arginine metabolism. Annual Review of Nutrition, 22, 87-105. https://doi.org/10.1146/annurev.nutr.22.110801.140547
Rothman, D. L., Magnusson, I., Katz, L. D., Shulman, R. G., & Shulman, G. I. (1991). Quantitation of hepatic glycogenolysis and gluconeogenesis in fasting humans with 13C NMR. Science, 254(5031), 573-576. https://doi.org/10.1126/science.1948033
Reading the NS 230 Unit 2 instructions
The fate summary unit asks students to describe what happens to each macronutrient after absorption: where it goes, how it is stored or used and what it can be converted into. Prompts usually expect separate treatment of glucose, fatty acids and amino acids, with tissues and key enzymes named. Organize by fuel and, within each, by first stop and later destinations. Mark clearly which conversions the body can make and which it cannot, and explain why for the most important gaps, such as fatty acids to glucose. Include ketone bodies as a fate of fatty acids when carbohydrate is scarce. Note how timing, fed or fasting, changes the fates. Cite a biochemistry text or review. Four to five pages is typical.
How this NS230 Unit 2 example is built
An opening explains why fates matter. The glucose section follows the portal vein to liver glycogen, then muscle, brain and red blood cells, lists available conversions and names two that are impossible. The fatty acid section follows chylomicrons, lipoprotein lipase, adipose storage, beta-oxidation and ketone formation, and explains why acetyl-CoA cannot return to pyruvate, which the highlighted sentence identifies as the most consequential gap. The amino acid section covers liver uptake, branched-chain amino acids, protein use and urea. A section on shared intermediates and another on timing across the day lead to a summary of routes and a fasting example. Each fuel's section ends by listing what that fuel can never become.
Reading the NS230 Unit 2 grading rubric
NS230 fate summaries tend to be scored on accuracy and completeness first: correct tissues, storage forms and conversions for all three fuels. Points go to marking impossible conversions and explaining the reason for the key ones, which shows understanding beyond memorization. Organization that lets a reader follow each fuel is credited under clarity. Linking fates to the fed and fasting states earns credit for integration. Use of a credible text or review, cited correctly, counts under evidence. A summary that states fatty acids can become glucose, or omits the absence of a protein store, usually loses significant accuracy points. Linking each impossible conversion to the enzyme step that blocks it is often what separates strong work from adequate work.
NS230 Unit 2 help: mistakes that cost points
Fate summaries often list pathways for each fuel without saying where they happen or when. Another common error is stating that fat can be converted to glucose, missing the irreversible pyruvate dehydrogenase step. Students sometimes forget the glycerol backbone, which can become glucose. Amino acids are frequently described as stored, though the body has no protein reserve. Ketone bodies are either omitted or given too much space. Impossible conversions are rarely marked. If you are building a summary and losing track of which routes exist, draw the three fuels meeting at pyruvate and acetyl-CoA, and a writer can help you mark each route from that sketch.
Get an NS230 Unit 2 example written to your instructions
Tell us which foods or which fuel your Unit 2 prompt emphasizes, and paste in its instructions and grading criteria. The summary is built fuel by fuel in the same destination-first layout, tables included where your section expects them. It reaches you inside 24-48h, and you pay nothing for the first. The paper above is an original model document written by our desk, not a submitted student paper and not an official Purdue University Global document.
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- NS230 Unit 5: Lipid Metabolism Case Study
- NS230 Unit 6: Seminar Reflection
- NS230 Unit 7: Protein Turnover Analysis
- NS230 Unit 8: Hormonal Regulation Summary
- NS230 Unit 9: Fed and Fasted Comparison
- NS230 Unit 10: Integrated Metabolism Paper
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NS230 Unit 2 questions, answered
How much detail does each pathway need here?
Less than later units will ask for. The fate summary names each destination, the tissue, and the one enzyme that marks the route, glycogen synthase, lipoprotein lipase, an aminotransferase, without walking every step. Later units in many sections take single pathways apart in detail, so a fate summary that tries to do their job runs long and loses its comparison.
Can fatty acids really never become glucose?
Not in net terms for the even-chain fatty acids that dominate the diet. Their carbons enter the citric acid cycle as acetyl-CoA, and two carbons leave as carbon dioxide on each turn, so nothing is left over to build glucose. The glycerol backbone of a triglyceride can become glucose, and odd-chain fatty acids contribute a small amount through propionyl-CoA.
Should ketone bodies appear in a fate summary?
Briefly, as a fate of fatty acids in the liver when carbohydrate is scarce. One or two sentences naming their production in liver mitochondria and their use by muscle, heart and, after some days of fasting, the brain are usually enough. The detailed regulation belongs to later units on fasting, and your summary can say so rather than borrowing it early.
Where can I find a free NS230 Unit 2 sample paper?
This page presents a complete Unit 2 macronutrient fate summary following glucose, fatty acids and amino acids, with impossible conversions marked and APA references.
Why can't fatty acids become glucose?
Even-chain fatty acids are broken down to acetyl-CoA, and pyruvate dehydrogenase cannot run backward to turn acetyl-CoA into pyruvate. The carbons acetyl-CoA brings into the citric acid cycle are lost as carbon dioxide.