Question

The substrate for photorespiration is which of the following?
A. Serine
B. Glycolate
C. Indole acetic acid
D. Malic acid

Answer 1

Hint: Photorespiration is a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, which waste some energy produced by photosynthesis. This process reduces the efficiency of the photosynthesis process by reducing photosynthetic output by 25% in some plants.

Complete answer:
With the addition of the molecular oxygen to ribulose-1, 5-bisphosphate produces 3-phosphoglycerate and 2-phosphoglycolate. Certain enzymes are inhibited by the Phosphoglycolate involved in photosynthetic carbon fixation. Salvaged in a series of reactions in the peroxisome, mitochondria and then again in the peroxisome where it gets converted into glycerate. Glycerate re- enters the chloroplast of the plants by the same transporter that helps in export of glycolate.
Photorespiration leads to the loss of fixed carbon dioxide in some plants by the enzyme called RuBisCO. During the process of photorespiration, this enzyme reacts with the oxygen instead of the carbon dioxide to form ribulose 1, 5 bisphosphate which produces phosphoglycolate as the very first product. The glycolate is generated by dephosphorylation of phosphoglycolate which is the actual product of the photorespiration. There are several reactions occurring along with this pathway which include the production of hydrogen peroxide in the peroxisome. Hydrogen peroxide is a dangerous strong oxidant which should be immediately split into water and oxygen by an enzyme catalase.

Hence, the correct option is B. Glycolate.

Note: Cyanobacteria have three pathways in which they can possibly metabolise 2-phosphoglycolate. If all three pathways are blocked then they are unable to grow despite having carbon concentration mechanisms that should reduce the rate of photorespiration.