Question 1: Look at table 17.2 to see the standard free energy changes for the steps in the CAC. Three consecutive steps in the cycle appear to be the most readily reversible (having standard free energy changes closest to zero). Which are these steps?
Question 1: Look at table 17.2 to see the standard free energy changes for the steps in the CAC. Three consecutive steps in the cycle appear to be the most readily reversible (having standard free energy changes closest to zero). Which are these steps?
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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Question 1: Look at table 17.2 to see the standard free energy changes for the steps in the CAC. Three consecutive steps in the cycle appear to be the most readily reversible (having standard free energy changes closest to zero). Which are these steps?
Transcribed Image Text:TABLE 17.2 Citric acid cycle
Step
1
2a
2b
3
4
Reaction
Acetyl CoA + oxaloacetate+ H₂O → citrate + CoA + H+
Citratecis-aconitate + H₂O
cis-Aconitate + H₂Oisocitrate
Isocitrate + NAD
a-ketoglutarate + CO₂ + NADH
α-Ketoglutarate + NAD+ +COA
succinyl CoA + CO₂ + NADH
Enzyme
Citrate
synthase
Aconitase
Aconitase
Isocitrate
dehydrogenase
a-
Prosthetic Type*
group
Fe-S
Fe-S
Lipoic
acid, FAD,
Ketoglutarate
dehydrogenase TPP
complex
a
b
d+e
d+e
AG"
kJ mol-1
-31.4
+8.4
-2.1
-8.4
-30.1
kcal mol
1
-7.5
+2.0
-0.5
-2.0
-7.2
Transcribed Image Text:Step
5
6
7
TABLE 17.2 Citric acid cycle
8
Reaction
Succinyl CoA+R+ADP
succinate+ATP+COA
Succinate+FAD (enzyme-bound)
fumarate+FADH, (enzyme-bound)
Fumarate + H₂O = L-malate
-Malate+NAD
Enzyme
Oxaloacetate+NADH+H
Succinyl CoA
synthetase
Succinate
dehydrogenase
Fumarase
Malate
Prosthetic
group
FAD, Fe-S
Type* kJ mol-¹
f
e
C
AG"
e
-3.3
0
-3.8
+29.7
kcal mol-¹
-1
-0.8
0
-0.9
dehydrogenase
*Reaction type: (a) condensation; (b) dehydration; (c) hydration; (d) decarboxylation; (e) oxidation; (f) substrate-level
phosphorylation.
+7.1
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