Page 161 - PG 101-Course notes مذكرة النظري 24-25 with spec

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

➢ When it is hot and dry, plants keep their stomata closed to prevent water loss.

At the same time, O 2 (a waste product of the photosynthesis) builds up in the

leaf, and more CO 2 cannot be acquired from the atmosphere (C3 plants)

▪ RuBISCO has two activities: (Ribulose Bisphosphate Carboxylase/Oxidase)

(1) Carobxylase reaction (useful, good):

RuBP (Ribulose 1,5 bisphosphate) + CO 2 → 2 PGA

Stores energy in reduced carbon compounds; anabolic; carbon is fixed.

(2) Oxygenase reaction (wastes energy, Bad):

RuBP (Ribulose 1,5 bisphosphate) + O 2 → 1 PGA + 1 phospho-

glycolate (2C)

only 1 PGA is made instead of 2 & phosphoglycolate must be broken

down or salvaged through a complex set of reactions.

o Photorespiration salvage pathway:

- Needs enzymes in 3 organelles (chloroplasts, peroxisomes & mitochondria).

- Consumes O2 & releases CO2 “respiration”.

- Consumes a lot of energy (ATP, NADPH).

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