According to Table 17.1, several reactions have very positive G' values. How can this be explained, given

According to Table 17.1, several reactions have very positive ΔG°' values. How can this be explained, given that these reactions do occur in the cell?

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Table 17.1 Step Reaction 1 Glucose + ATP → Glucose-6-phosphate + ADP 2 Glucose-6-phosphate →Fructose-6-phosphate 3 Fructose-6-phosphate + ATP→Fructose-1, 6-bisphosphate + ADP 4 Fructose-1,6-bisphosphate →Dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate The Reactions of Glycolysis and Their Standard Free-Energy Changes 5 Dihydroxyacetone phosphate → Glyceraldehyde- 3-phosphate 6 2(Glyceraldehyde-3-phosphate + NAD+ + P₁ → 1,3-bisphosphoglycerate + NADH + H+) 7 2(1,3-bisphosphoglycerate + ADP→→ 3-Phosphoglycerate + ATP) 8 2(3-Phosphoglycerate → 2-Phosphoglycerate) 9 2(2-Phosphoglycerate → 10 Overall Phosphoenolpyruvate + H₂O) 2(Phosphoenolpyruvate + ADP → Pyruvate + ATP) - Glucose + 2ADP + 2P; + NAD+ - 2 Pyruvate 2ATP + NADH + H+ 2(Pyruvate + NADH + H+ → Lactate + NAD+) Glucose + 2ADP + 2P→2 Lactate + 2ATP Enzyme Hexokinase/Glucokinase Glucose phosphate isomerase Phosphofructokinase Aldolase Triose phosphate isomerase Glyceraldehyde-3-P dehydrogenase Phosphoglycerate kinase Phosphoglyceromutase Enolase Pyruvate kinase Lactate dehydrogenase kJ mol-¹ -16.7 +1.67 -14.2 +23.9 +7.56 AG** 2(+6.20) 2(-18.8) 2(+4.4) 2(+1.8) 2(-31.4) -73.3 2(-25.1) -123.5 kcal mol-¹ -4.0 +0.4 -3.4 +5.7 +1.8 2(+1.5) 2(-4.5) 2(+1.1) 2(+0.4) 2(-7.5) -17.5 2(-6.0) - 29.5 AG** kJ mol-¹ -33.9 -2.92 -18.8 -0.23 +2.41 2(-1.29) 2(+0.1) 2(+0.83) 2(+1.1) 2(-23.0) -98.0 2(-14.8) -127.6