Question

1. Describe the different steps whereby a molecule of sucrose is oxidized to CO₂ in glycolysis, the pentose phosphate pathway and the citric acid cycle. Indicate in which steps CO₂ is released, and in which steps energy is conserved.

Answer 1

Sucrose is made up of glucose and fructose. Glucose enters the glycolysis cycle in the first step while fructose gets converted to fructose-6-phosphate and then enters the 3rd step of the cycle. Pyruvate is the last step of glycolysis. 2 ATP molecules are formed in the following 2 steps of glycolysis:

• 1, 3 bisphosphoglycerate to 3 phosphoglycerate
• PEP to pyruvate

This pyruvate then enters the TCA cycle. CO2 is released in the conversion of pyruvate to acetyl coA. In the conversion of isocitrate to alpha ketogluterate also one CO2 is released. In the conversion of alpha ketogluterate to succinyl coA also one CO2 is released. In the conversion of succinyl coA to succinate, a GTP is formed.

In the pentose phosphate pathway:

In the conversion of 6-phosphogluconate to ribulose 5 phosphate CO2 is released