What is Carbohydrate Metabolism?
Carbohydrate metabolism is how the body breaks down, stores, and rebuilds sugars for energy. Glucose can be oxidized immediately through glycolysis or stored as glycogen in the liver and muscles for later use.
Carbohydrate metabolism covers glycolysis (glucose → pyruvate + ATP), glycogenesis (glucose → glycogen storage), and glycogenolysis (glycogen → glucose release), keeping blood glucose stable and supplying cells with energy.
- 1.Glucose Uptake — Dietary glucose enters cells via GLUT transporters, raising blood glucose after a meal.
- 2.Glycogenesis — Excess glucose is linked into branched glycogen chains in the liver and muscle, driven by insulin.
- 3.Glycogenolysis — Between meals, glycogen phosphorylase breaks glycogen back into glucose-1-phosphate, triggered by glucagon or adrenaline.
- 4.Glycolysis — Released glucose is split into pyruvate in the cytoplasm, yielding a net 2 ATP and 2 NADH per glucose.
Step-by-step worked examples
One glucose molecule goes through glycolysis. The investment phase uses 2 ATP and the payoff phase produces 4 ATP. What is the net ATP yield?
ATP produced − ATP invested 4 ATP − 2 ATP = 2 ATP Result: net yield is 2 ATP per glucose (plus 2 NADH)
A liver glycogen granule holds 12,000 glucose units. Glycogen phosphorylase releases one glucose-1-phosphate per residue removed. How many glucose-1-phosphate molecules come from breaking down the whole granule?
Each glucose unit removed yields one glucose-1-phosphate 12,000 units × 1 G1P/unit = 12,000 G1P Result: 12,000 glucose-1-phosphate molecules released
Glycogenesis adds 800 glucose units to a glycogen chain, costing about 1 UTP-equivalent high-energy bond per glucose added. How many high-energy bonds are consumed?
Bonds consumed = glucose units added × 1 bond/unit 800 × 1 = 800 Result: 800 high-energy phosphate bonds are used
Flashcards
Quick quiz
Q1.What is the net ATP yield of glycolysis per glucose molecule?
Q2.Which hormone triggers glycogenolysis when blood sugar is low?
Q3.Where does glycolysis take place in the cell?
Q4.Which organ's glycogen can directly raise blood glucose levels?
The full card deck, worked steps and AI-tutor support for “What is Carbohydrate Metabolism?” are in Notek — study by hand before your exam.
Common mistakes
Glycolysis requires oxygen to occur. — Correct: Glycolysis is anaerobic; oxygen is only needed for the later stages of aerobic respiration (Krebs cycle and electron transport chain).
Muscle glycogen can raise blood glucose like liver glycogen. — Correct: Muscle cells lack glucose-6-phosphatase, so they can only use glycogen for their own energy, not release it into the blood.
Glycogenesis and glycogenolysis are the same process running in reverse with identical enzymes. — Correct: They use different, hormonally-regulated enzyme sets (glycogen synthase for synthesis, glycogen phosphorylase for breakdown) so both can be controlled independently.
Glycolysis fully oxidizes glucose to CO2 and water. — Correct: Glycolysis only converts glucose to pyruvate; full oxidation requires the Krebs cycle and oxidative phosphorylation.
FAQ
What is carbohydrate metabolism?
It's the set of pathways — glycolysis, glycogenesis, and glycogenolysis — that break down, store, and release glucose to supply cellular energy.
What is the formula for the net ATP yield of glycolysis?
Net ATP = ATP produced in payoff phase − ATP invested = 4 − 2 = 2 ATP per glucose.
What are examples of carbohydrate metabolism in the body?
Storing extra glucose as liver glycogen after a meal, and breaking that glycogen down between meals to keep blood sugar stable.
How do you calculate glucose released from glycogen breakdown?
Multiply the number of glucose residues removed by 1 glucose-1-phosphate per residue, since glycogen phosphorylase removes one unit at a time.