Instant Notes: Plant Biology

The chief carbohydrate storage products from photosynthesis are sugarsand

starch. These are respired by plant cells to provide ATP. Respirationoccurs in

all cells, whether photosynthetic or not. Starch is made up of glucose polymers,

either as long, straight chain molecules, amylose, or in highly branched form,

amylopectin. Starch is mostly deposited in plastids. Fig. 1shows the two major

pathways for starch breakdown, either involving hydrolytic enzymes,

Starch
degradation

J4 – Respiration and carbohydrate metabolism 149

Starch

phosphorolytic

glucose-1-P

Starch Sucrose

fructose

hydrolytic

glucose

glucose-6-P

fructose-6-P

fructose-1,6-bisphosphate

dihydroxyacetone-P glyceraldehyde-3-P

1,3-bisphosphoglycerate

3-phosphoglycerate

2-phosphoglycerate

phosphoenolpyruvate

pyruvate

AT P

ADP

AT P

ADP

ADP

AT P

ADP

AT P

NAD+

NADH

AT P

ADP

Pi

Instant Notes

Fig. 1. The major pathways of starch degradation in a plant cell, involving either hydrolytic or

phosphorylytic enzymes. All pathways lead into glycolysis.