Describe the HMP shunt and add a note on its significance.

1. 1 · Open in two lines. The HMP shunt (pentose phosphate pathway) is a side route for glucose-6-phosphate in the cytoplasm. It makes NADPH and ribose-5-phosphate, not ATP.
2. 2 · Say where it happens. Liver, adipose tissue, adrenal cortex, lactating mammary gland and red blood cells.
3. 3 · Draw the pathway. [Diagram: glucose-6-P → 6-phosphogluconolactone → 6-phosphogluconate → ribulose-5-P, then the non-oxidative exchanges back to fructose-6-P and glyceraldehyde-3-P; NADPH, CO2 and TPP marked]
4. 4 · Write the two phases.
   • Oxidative (one-way): G6PD, lactonase, 6-phosphogluconate dehydrogenase; 2 NADPH + 1 CO2 per glucose-6-P.
   • Non-oxidative (reversible): isomerase, epimerase, transketolase (TPP), transaldolase.
5. 5 · Overall balance. 3 glucose-6-P → 6 NADPH + 3 CO2 + 2 fructose-6-P + 1 glyceraldehyde-3-P. No ATP is made.
6. 6 · Significance. NADPH for fatty acid, cholesterol and steroid synthesis and for reduced glutathione; ribose-5-P for nucleotides.
7. 7 · Nutrition link. G6PD deficiency causes haemolysis after fava beans or primaquine; transketolase needs thiamine.
8. 8 · Close in one line. Sum up the shunt as the cell's NADPH factory rather than an energy pathway.

Scoring tip: Write 'No ATP is produced' clearly. Examiners look for it, along with G6PD deficiency.