Question

3) Calculate the energy yield or cost, in ATP equivalents, for the following processes:

A) glycogen (3 residues from one nonreducing end) → 6 pyruvate

B) 3 glucose → 6 pyruvate

C) 6 pyruvate → 3 glucose

Answer 1

Glycogen----3 G1P (by glycogen phosphorylase)

3 G1P ------ 3 G6P (by phosphoglucomutase)

From G6P to 2 pyruvate, input 1 ATP (by phosphofuctoase kinase)

output 4 ATP Net yield 3 ATP

Thus, from 3 residue of glycogen to 6 pyruvate: 3 x 3 = 9 ATP.(+9)

(B)Stage I, input2 ATP per glucose Stage II: output 4 ATP per glucose Net yield is 2 ATP per glucose. Thus, 3 glucose to 6 pyruvate will be 6 ATP.(+6)

(C) 2 pyruvate to 1 glucose costs 6 ATP: 2 each at the steps catalyzed by pyruvate carboxylase;PEPCK and phosphoglycerate kinaseThus, 6 pyruvate to 3 glucose needs 18 ATP input(-18)