Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

ATP PRODUCTION IN MITOCHONDRIA
775
Table 14–1 Product Yields from the Oxidation of Sugars and Fats
A. Net products from oxidation of one molecule of glucose
In cytosol (glycolysis)
1 glucose → 2 pyruvate + 2 NADH + 2 ATP
In mitochondrion (pyruvate dehydrogenase and citric acid cycle)
2 pyruvate → 2 acetyl CoA + 2 NADH
2 acetyl CoA → 6 NADH + 2 FADH 2 + 2 GTP
Net result in mitochondrion
2 pyruvate → 8 NADH + 2 FADH 2 + 2 GTP
B. Net products from oxidation of one molecule of palmitoyl CoA (activated form
of palmitate, a fatty acid)
In mitochondrion (fatty acid oxidation and citric acid cycle)
1 palmitoyl CoA → 8 acetyl CoA + 7 NADH + 7 FADH 2
8 acetyl CoA → 24 NADH + 8 FADH 2 + 8 GTP
Net result in mitochondrion
1 palmitoyl CoA → 31 NADH + 15 FADH 2 + 8 GTP
phosphorylation, each pair of electrons donated by the NADH produced in mitochondria
can provide energy for the formation of about 2.5 molecules of ATP. Oxidative
phosphorylation also produces 1.5 ATP molecules per electron pair from
the FADH 2 produced by succinate dehydrogenase in the mitochondrial matrix,
and from the NADH molecules produced by glycolysis in the cytosol. From the
product yields of glycolysis and the citric acid cycle, we can calculate that the
complete oxidation of one molecule of glucose—starting with glycolysis and ending
with oxidative phosphorylation—gives a net yield of about 30 molecules of
ATP. Nearly all this ATP is produced by the mitochondrial ATP synthase.
In Chapter 2, we introduced the concept of free energy (G). The free-energy
change for a reaction, ∆G, determines whether that reaction will occur in a cell.
We showed on pp. 60–63 that the ∆G for a given reaction can be written as the sum
of two parts: the first, called the standard free-energy change, ∆G°, depends only
on the intrinsic characters of the reacting molecules; the second depends only on
their concentrations. For the simple reaction A → B,
[B]
∆G = ∆G° + RT ln
[A]
where [A] and [B] denote the concentrations of A and B, and ln is the natural logarithm.
∆G° is the standard reference value, which can be seen to be equal to the
value of ∆G when the molar concentrations of A and B are equal (since ln 1 = 0).
In Chapter 2, we discussed how the large, favorable free-energy change (large
negative ∆G) for ATP hydrolysis is used, through coupled reactions, to drive
many other chemical reactions in the cell that would otherwise not occur (see
pp. 65–66). The ATP hydrolysis reaction produces two products, ADP and P i ; it is
therefore of the type A → B + C, where, as demonstrated in Figure 14–29,
∆G = ∆G° + RT ln
[B][C]
[A]
When ATP is hydrolyzed to ADP and P i under the conditions that normally
exist in a cell, the free-energy change is roughly –46 to –54 kJ/mole (–11 to –13
kcal/mole). This extremely favorable ∆G depends on maintaining a high concentration
of ATP compared with the concentrations of ADP and P i . When ATP, ADP,
and P i are all present at the same concentration of 1 mole/liter (so-called standard
conditions), the ∆G for ATP hydrolysis drops to the standard free-energy change
(∆G°), which is only –30.5 kJ/mole (–7.3 kcal/mole). At much lower concentrations
of ATP relative to ADP and P i , ∆G becomes zero. At this point, the rate at