Page 163 - PG 101-Course notes مذكرة النظري 24-25 with spec

Medicinal plants (PG 101) Level 1 Clinical Pharmacy-PharmD

The C4 Pathway (Hatch-Slack pathway):

(1) The initial carboxylation reaction occurs in the mesophyll cells which contain PEP

carboxylase enzyme that fixes CO 2 into oxaloacetate (4C compound).

CO 2 + PEP (phosphoenolpyruvate, 3C comp) → oxaloacetate (OAA)

(2) Oxaloacetate is then converted into malate (another 4C acid) which exits

Mesophyll cells & enters Bundle sheath cells.

(3) In bundle sheath cells, malate is decarboxylated releasing CO 2 → ↑ CO 2 conc. in

bundle sheath cells where it can be fixed into carbohydrate by Calvin cycle.
Carbohydrate is then moved into the vascular bundle & translocated to the rest of the

plant.

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