Describe gluconeogenesis. Add a note on the Cori cycle.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open in two lines. Gluconeogenesis is the making of glucose from non-carbohydrate sources. It happens mainly in the liver, and also in the kidney, during fasting.
2 · List the substrates. Lactate, glycerol, glucogenic amino acids and propionate, with where each enters.
3 · Draw the pathway. [Diagram: pyruvate → oxaloacetate → PEP → … → fructose-1,6-bisP → fructose-6-P → glucose-6-P → glucose, with the 4 bypass enzymes boxed and substrate entry points marked]
4 · Explain the three bypass reactions.
Pyruvate → oxaloacetate → PEP: pyruvate carboxylase (biotin, ATP) and PEP carboxykinase (GTP).
5 · Energy cost and Cori cycle. 6 high-energy bonds (4 ATP + 2 GTP) per glucose. Muscle lactate is recycled to glucose in the liver (Cori cycle).
6 · Significance. Keeps blood glucose up in fasting for the brain and red blood cells; clears lactate and glycerol. Glucagon and cortisol switch it on; insulin switches it off.
7 · Nutrition link. Biotin is needed for pyruvate carboxylase; excess gluconeogenesis raises fasting blood sugar in diabetes.
8 · Close in one line. Sum up gluconeogenesis as the body's way of making glucose when food glucose is not available.
Scoring tip: Box the four bypass enzymes on your diagram. Examiners look for these names first.
Write-up practice
The check looks for key words only. It does not grade your answer and never writes it for you.