What is Glycolysis?
Glycolysis is the universal first step of glucose breakdown, splitting one glucose molecule into two pyruvate molecules while producing ATP and NADH. When oxygen is absent, fermentation regenerates NAD+ so glycolysis can continue.
Glycolysis converts one glucose (C6H12O6) into two pyruvate molecules, netting 2 ATP and 2 NADH; without oxygen, fermentation recycles NADH back to NAD+ via lactic acid or alcoholic pathways.
- •Occurs in muscle cells and some bacteria
- •Pyruvate is reduced directly to lactate
- •Regenerates NAD+ without releasing CO2
- •Causes the muscle burn felt during intense exercise
- •Occurs in yeast and some bacteria
- •Pyruvate is converted to ethanol + CO2 in two steps
- •Regenerates NAD+ while releasing CO2
- •Used in brewing, baking and winemaking
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Step-by-step worked examples
A cell processes 5 glucose molecules through glycolysis. How much net ATP is produced?
Net ATP per glucose = 2 Total = 5 × 2 = 10 ATP
Glycolysis invests 2 ATP and produces 4 ATP in the payoff phase for one glucose. What is the net gain?
Net ATP = produced − invested Net ATP = 4 − 2 = 2 ATP
A muscle cell ferments 8 pyruvate molecules to lactate during sprinting (1 NADH oxidized per pyruvate reduced). How many NAD+ are regenerated?
NAD+ regenerated = number of pyruvate molecules reduced NAD+ regenerated = 8
Flashcards
Quick quiz
Q1.Glycolysis splits one glucose molecule into:
Q2.What is the net ATP yield of glycolysis?
Q3.Why does fermentation occur when oxygen is absent?
Q4.Which fermentation pathway produces ethanol and CO2?
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Common mistakes
Glycolysis requires oxygen. — Correct: Glycolysis is anaerobic — it happens in the cytoplasm regardless of oxygen availability.
Fermentation produces a lot of extra ATP. — Correct: Fermentation itself produces no additional ATP; its role is regenerating NAD+ so glycolysis can keep making its 2 ATP.
Lactic acid and alcoholic fermentation are the same process. — Correct: Lactic acid fermentation reduces pyruvate to lactate directly; alcoholic fermentation converts it to ethanol and CO2 in two steps.
Glycolysis only happens in humans. — Correct: Glycolysis is nearly universal — it occurs in bacteria, plants, fungi and animals.
FAQ
What is glycolysis?
The metabolic pathway that splits glucose into two pyruvate molecules, producing net 2 ATP and 2 NADH.
What is the formula for glycolysis?
C6H12O6 + 2NAD+ + 2ADP + 2Pi → 2 Pyruvate + 2NADH + 2ATP + 2H2O.
What are examples of fermentation?
Lactic acid fermentation in muscle cells, and alcoholic fermentation by yeast in brewing and baking.
How is glycolysis ATP yield calculated?
Subtract the 2 ATP invested in the investment phase from the 4 ATP produced in the payoff phase, giving a net of 2 ATP.