Biomedical Engineering Reference
In-Depth Information
H
N
O
O
NH
H
O
O
OH
N
OH
N
P
O
P
O
OH
NH
2
N
HO
O
OH
N
O
N
N
OH
OH
(FADH
2
)
-2 H
+ 2 H
H
N
O
O
N
O
O
OH
N
OH
N
O
P
O
P
OH
NH
2
N
HO
O
OH
N
O
N
N
Ribitol
Flavin or
Vitamin B
2
ADP
(FAD)
OH
OH
FIGURE 10.24
The redox of flavin adenine dinucleotide (FAD) and FADH
2
.
Note from
Fig. 10.22
that GTP can be converted easily into ATP; some descriptions of the
TCA cycle show directly the conversion of ADP plus phosphorus into ATP, as succinyl-CoA
is converted to succinate.
The major roles of the TCA cycle are (1) to provide electrons (NADH) for the electron
transport chain and biosynthesis, (2) to supply C skeletons for amino acid synthesis, and
(3) to generate energy.
Many of the intermediates in the TCA cycle are used extensively in biosynthesis.
Removal of these intermediates “short-circuits” the TCA cycle. To maintain a functioning
TCA cycle, the cell can fix CO
2
(heterotrophic CO
2
fixation) or supply acetyl-CoA via
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