NS230 Unit 3 Glycolysis Problem Set Example

Course	NS230 Macronutrient Metabolism
Unit	Unit 3
Paper type	Glycolysis problem set
Length	About 920 words, 6 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 3

Where ATP Is Spent and Where It Is Made: A Unit 3 Glycolysis Problem Set Worked Through Six Problems

[Student Name]

Purdue University Global

NS230: Macronutrient Metabolism

Unit 3 Glycolysis Problem Set

[Instructor Name]

[Date]

The problems are constructed for illustration; the biochemistry and exercise sources cited are real.

What this part is doingPromising to trace every yield to its reaction in the lead tells the grader the set is graded on reasoning, not recall.

Reference: The Pathway in Brief

Glycolysis converts one glucose molecule to two pyruvate molecules in the cytosol through ten reactions. The first phase spends energy: hexokinase phosphorylates glucose to glucose-6-phosphate, using one ATP; phosphofructokinase-1 phosphorylates fructose-6-phosphate to fructose-1,6-bisphosphate, using a second ATP. Aldolase then splits the six-carbon sugar into two three-carbon molecules. The second phase, run twice for each glucose, makes energy: glyceraldehyde-3-phosphate dehydrogenase produces NADH, phosphoglycerate kinase produces one ATP, and pyruvate kinase produces another ATP. The three regulated, essentially irreversible steps are those catalyzed by hexokinase, phosphofructokinase-1 and pyruvate kinase (Berg et al., 2019).

Problem 1: Net ATP From One Glucose

Question: How much ATP does glycolysis produce, net, from one glucose molecule?

Working. The investment phase spends 2 ATP, one at hexokinase and one at phosphofructokinase-1. The payoff phase runs twice, once for each three-carbon molecule. Each run produces 1 ATP at phosphoglycerate kinase and 1 ATP at pyruvate kinase, so 2 per run and 4 in total.

Answer: 4 produced minus 2 spent equals a net of 2 ATP per glucose, plus 2 NADH.

Problem 2: Starting From Glycogen

Question: In muscle, glucose units come from glycogen as glucose-1-phosphate, which is converted to glucose-6-phosphate without spending ATP. What is the net ATP yield per glucose unit?

Working. The hexokinase step is skipped, because glycogen phosphorylase uses inorganic phosphate rather than ATP to release glucose-1-phosphate. Only the phosphofructokinase-1 step spends ATP. The payoff phase still produces 4 ATP.

Answer: 4 produced minus 1 spent equals a net of 3 ATP per glucose unit from glycogen. This is one reason muscle glycogen is such an efficient fuel for rapid, intense activity.

Problem 3: What Happens to the NADH Without Oxygen

Question: During a sprint, oxygen delivery cannot keep pace with demand. Glycolysis needs NAD+ at the glyceraldehyde-3-phosphate dehydrogenase step. Where does it come from?

Working. Without enough oxygen for the electron transport chain to reoxidize NADH, the cell regenerates NAD+ by reducing pyruvate to lactate through lactate dehydrogenase. Each pyruvate converted to lactate uses one NADH and returns one NAD+.

Answer: Lactate dehydrogenase regenerates the NAD+, so glycolysis can continue, with a net yield of 2 ATP per glucose, or 3 per glucose unit from glycogen. Muscle biopsies taken during ten short all-out cycling bouts found that the opening bout drew roughly half its energy from anaerobic glycolysis (Gaitanos et al., 1993).

The NADH made at one step must be returned as NAD+ at another, so in the absence of oxygen the cell sacrifices pyruvate to lactate not to make energy but to keep the energy-making step supplied.

What this part is doingThe highlighted sentence explains why lactate forms, showing understanding of the redox balance rather than a memorized fact.

Problem 4: With Oxygen

Question: With oxygen, the NADH from glycolysis is reoxidized through the mitochondria. If each cytosolic NADH yields about 1.5 ATP through the glycerol phosphate shuttle or about 2.5 ATP through the malate-aspartate shuttle, how much ATP do the 2 NADH from glycolysis add?

Working. With the glycerol phosphate shuttle: 2 times 1.5 equals 3 ATP. With the malate-aspartate shuttle: 2 times 2.5 equals 5 ATP.

Answer: The 2 NADH add 3 to 5 ATP depending on the shuttle, bringing glycolysis's contribution to 5 to 7 ATP per glucose before pyruvate enters the mitochondria. These figures follow the modern estimates rather than older whole-number values (Berg et al., 2019).

Problem 5: Regulation at Phosphofructokinase-1

Question: During intense exercise, ATP falls and AMP rises in muscle. What happens to phosphofructokinase-1, and why does it matter?

Working. Phosphofructokinase-1 is the main control point of glycolysis. It is inhibited by high ATP and by citrate, both signals that energy is plentiful, and activated by AMP, a signal that energy is running low. In liver, it is also strongly activated by fructose-2,6-bisphosphate.

Answer: Rising AMP relieves ATP's inhibition and activates phosphofructokinase-1, speeding glycolysis to match the muscle's demand. Because this step commits fructose-6-phosphate to glycolysis, controlling it controls the pathway's overall flow (Hargreaves & Spriet, 2020).

Problem 6: Carbon Bookkeeping

Question: Six carbons enter as glucose. Where are they at the end of glycolysis, and where do they go next with and without oxygen?

Working. Glycolysis conserves all six carbons in two three-carbon pyruvate molecules. With oxygen, pyruvate dehydrogenase converts each pyruvate to acetyl-CoA and carbon dioxide, releasing one carbon per pyruvate; the remaining two carbons per acetyl-CoA enter the citric acid cycle and leave as carbon dioxide. Without oxygen, pyruvate becomes lactate, keeping all three carbons.

Answer: After glycolysis, six carbons are in two pyruvate. With oxygen, all six eventually leave as carbon dioxide. Without oxygen, all six remain in two lactate molecules, which can be carried to the liver and made back into glucose, the subject of the next unit.

Summary of Yields

1. Glucose to pyruvate: net 2 ATP and 2 NADH.

2. Glycogen unit to pyruvate: net 3 ATP and 2 NADH.

3. Glucose to lactate: net 2 ATP, with no net NADH.

4. Cytosolic NADH reoxidized aerobically: about 1.5 or 2.5 ATP each, depending on the shuttle.

Common Errors

The most common error in glycolysis problems is forgetting that the payoff phase runs twice per glucose. The second is counting NADH as ATP without saying which shuttle carries it. The third is assuming glycogen and glucose give the same yield, missing the ATP saved when phosphorylase releases glucose-1-phosphate.

What this part is doingNaming the common errors shows the writer knows where bookkeeping goes wrong.

References

Berg, J. M., Tymoczko, J. L., Gatto, G. J., Jr., & Stryer, L. (2019). Biochemistry (9th ed.). W. H. Freeman.

Gaitanos, G. C., Williams, C., Boobis, L. H., & Brooks, S. (1993). Human muscle metabolism during intermittent maximal exercise. Journal of Applied Physiology, 75(2), 712-719. https://doi.org/10.1152/jappl.1993.75.2.712

Hargreaves, M., & Spriet, L. L. (2020). Skeletal muscle energy metabolism during exercise. Nature Metabolism, 2(9), 817-828. https://doi.org/10.1038/s42255-020-0251-4

NS230 Unit 3 instructions, in plain terms

The problem set unit asks students to calculate energy yields and explain regulation in glycolysis. Prompts usually present several problems: net ATP from glucose, yield from glycogen, the fate of NADH with and without oxygen, regulation at control points and sometimes carbon accounting. Show every step, naming the enzyme where ATP is spent or made. Remember that the payoff phase runs twice per glucose. Say which shuttle you assume when converting NADH to ATP, and use current estimates. Explain regulation by naming the effector and what it signals. Give a short answer after each working. Name common errors. Cite a biochemistry text for values. About four pages is typical.

Inside the NS230 Unit 3 example

A reference section summarizes the ten reactions and the three regulated steps. Problem one totals the net yield from glucose; problem two shows why glycogen gives one more ATP. Problem three explains lactate formation as a way to regenerate NAD+, citing sprint biopsy data, and the highlighted sentence states why lactate forms. Problem four adds the NADH under two shuttles, problem five explains phosphofructokinase-1 regulation during exercise and problem six tracks carbons with and without oxygen. A four-line summary of yields follows, and a closing section names three common errors. Every answer is boxed after its working, so a grader can find it quickly.

Reading the NS230 Unit 3 grading rubric

NS230 problem set rubrics usually give the most points to correct answers supported by clear working. Each yield should be traced to the specific reactions that produce or use ATP and NADH. Points go to correctly distinguishing glucose from glycogen as a starting point and to explaining the purpose of lactate formation. Regulation answers are scored on naming the right enzyme and effector and explaining what the effector signals. Use of current ATP estimates for NADH, with the shuttle stated, earns credit for accuracy. Organization and a cited source complete the rubric. Answers without working, or that count the payoff phase only once, generally lose points. Stating which shuttle is assumed for NADH is checked closely in most sections.

Common NS230 Unit 3 mistakes, and how to avoid them

Glycolysis problems trip students up most often on counting: the payoff phase happens twice per glucose, and forgetting it halves the yield. Another frequent error is treating NADH as if it were ATP without stating a shuttle or conversion value. Students often give glycogen the same yield as glucose. Lactate formation is commonly explained as a way to make energy rather than to regenerate NAD+. Regulation answers sometimes list effectors without saying what they signal. Older textbook values of 3 ATP per NADH appear in some answers. If you have a problem set and keep losing ATP in the count, write down each reaction that spends or makes ATP, and a writer can help you check the tally.

Get an NS230 Unit 3 example written to your instructions

Attach the Unit 3 problems exactly as your instructor set them, along with the rubric and whatever ATP counting convention the course uses. Every problem is worked on those terms, reaction table and tally shown, and returned in 24-48h. Nothing is charged for the first sample, regulation questions included if your set has them. 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 3 questions, answered

Should NADH be converted to ATP in the answer?

Only if the prompt asks for the complete oxidation of glucose. For glycolysis alone, report two NADH as NADH. If a later part of the set does carry them through, state the shuttle assumed, since the malate-aspartate and glycerol phosphate routes yield different amounts, and cite the figures your text uses. Mixing conventions within one set is a common source of lost points.

Why does starting from glycogen give three ATP?

Because glycogen phosphorylase uses inorganic phosphate, not ATP, to release glucose-1-phosphate, which is then isomerized to glucose-6-phosphate. The hexokinase step, and the ATP it would spend, is skipped. The rest of the pathway is identical, so the net rises from two to three. Show that reasoning in a line; a bare three with no explanation reads as memorized.

How much regulation belongs in a Unit 3 set?

Enough to name the three irreversible steps and the main effector on each: glucose-6-phosphate on hexokinase, ATP, AMP, citrate and fructose-2,6-bisphosphate on phosphofructokinase-1, and fructose-1,6-bisphosphate feeding forward to pyruvate kinase. Hormonal control usually gets its own unit later in the term, so a sentence noting that insulin and glucagon act through these enzymes is enough here.

Where can I find a free NS230 Unit 3 sample paper?

This page holds a complete Unit 3 glycolysis problem set with six worked problems, yields traced to reactions, margin notes and APA references.

Why does glycogen yield three ATP instead of two?

Glycogen phosphorylase releases glucose-1-phosphate using inorganic phosphate, so the hexokinase step that spends ATP is skipped. Only one ATP is spent in the investment phase instead of two.