Fundamentals of Anatomy and Physiology

Cellular Metabolism and Reproduction: Mitosis and Meiosis 65

Krebs citric acid cycle

Process two in respiration^

Pyruvic acid (C^3 )^

(^)
Acetic
acid (C 3 ) (^)
NAD CO (^2)
3 ATP made via e.t. (^) CoA enzyme
NADH 2
(^)
(^)
Oxaloacetic acid (C 4 )

FADH 2

FAD

2 ATP made via

e.t. (malic acid)

C^4

CO 2

2 NADH 2

2 NAD

6 ATP made via e.t.

(succinic acid)

C 4

Acetyl-CoA (C 2 ) COA

Citric acid (C 6 )

“ATP” ( = GTP)

CO (^2)
(^)
PO (^4)
“ADP” ( = GDP) (^) NAD (^)
NADH (^2)
(^) 3 ATP made via e.t. (^)
Ketoglutaric acid (C 5 )
GTP = Guanosine triphosphate e.t. = electron transport
This is equivalent to adenosine triphosphate
(^) ®
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Figure 4- 2 The Krebs citric acid cycle and its
products.
in this process: the cofactor NAD, the -cofactor FAD,
quinone, and the cytochrome system. There is some
debate as to whether the hydrogen protons (2H^1 ) are
transferred along with the electrons (2e^2 ) in this trans-port
or not. A currently accepted scheme is shown in Figure 4-3.
This scheme illustrates why the breakdown of glucose-
requires oxygen (O 2 ). Oxygen is the ultimate electron
acceptor for the electrons captured by the cofactors during
glucose decomposition. One ATP is formed during the first
step of electron transfer from NADH 2 to FAD. During the
following transfer from