Energy Production in Glycolysis
REFLECT AND APPLY According to Table, several reactions have very positive ΔG°' values. How can this be explained, given that these reactions do occur in the cell?
Table
Step | Reaction | Enzyme | ΔG °’* | ΔG** | ||
kJ mol-1 | kcal mol-1 | kJ mol-1 | ||||
1 | Glucose + ATP → Glucose-6-phosphate + ADP | Hexokinase/Glucokinase | -16.7 | -4.0 | -33.9 | |
2 | Glucose-6-phosphate → Fructose-6-phosphate | Glucose phosphate isomerase | + 1.67 | +0.4 | -2.92 | |
3 | Fructose-6-phosphate + ATP → Fructose-1, 6-bisphosphate + ADP | Phosphofructokinase | -14.2 | -3.4 | -18.8 | |
4 | Fructose-1,6-bisphosphate s Dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate | Aldolase | +23.9 | +5.7 | -0.23 | |
5 | Dihydroxyacetone phosphate → Glyceraldehyde-3-phosphate | Triose phosphate isomerase | +7.56 | +1.8 | +2.41 | |
6 | 2(Glyceraldehyde-3-phosphate + NAD+ + Pi → 1,3-bisphosphoglycerate + NADH + H+) | Glyceraldehyde-3-P dehydrogenase | 2( + 6.20) | 2( + 1.5) | 2(-1.29) | |
7 | 2(1,3-61sphosphoglycerate + ADP → 3-Phosphoglycerate + ATP) | Phosphoglycerate kinase | 2(-18.8) | 2(-4.5) | 2(+0.1) | |
8 | 2(3-Phosphoglycerate → 2-Phosphoglycerate) | Phosphoglyceromutase | 2(+4.4) | 2(+1.1) | 2(+0.83) | |
9 | 2(2-Phosphoglycerate → Phosphoenolpyruvate + H2O) | Enolase | 2( + 1.8) | 2(+0.4) | 2(+1.1) | |
10 | 2(Phosphoenolpyruvate + ADP → Pyruvate + ATP) | Pyruvate kinase | 2(-31.4) | 2(-7.5) | 2(-23.0) | |
Overall | Glucose + 2ADP + 2Pi + NAD+ → 2 Pyruvate → 2ATP + NADH + H+ 2(Pyruvate + NADH + H+ → Lactate + NAD+) Glucose + 2ADP + 2Pi → 2 Lactate + 2ATP | Lactate dehydrogenase | -73.3 2(-25.1) -123.5 | -17.5 2(-6.0) -29.5 | -98.0 2(-14.8) -127.6 |
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