Page 326 - Biology_F5

Gas exchange and respiration

The hydrogen atoms carried by reduced a total of 2 ATP molecules as it passes
NAD and FAD are transferred to a chain through the carriers. Initially, hydrogen
of other carriers at progressively lower atoms pass along the chain. However, after
energy levels. As the hydrogen passes the FAD stage, they split into protons (H )
+
from one carrier to the next, the energy and electrons. The former takes another
released is used to combine ADP and route out of the chain as the electrons
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inorganic phosphate (Pi) to form ATP. A pass through the cytochrome system.
series of carriers is termed the respiratory Accordingly, the pathway can be called
chain. The latter has four electron carriers, the electron transport system. Oxygen is
namely NAD, FAD, coenzyme Q and the final electron acceptor in the electron
cytochromes. The hydrogen atoms carried transport system. Finally, protons and
by NAD are shunted into the chain at electrons recombine to form hydrogen
carrier one, NAD (a step ahead FAD), and atoms which create a link with oxygen
produce a total of 3 ATP molecules as they to form water, this reaction is catalysed
pass through the carriers (Figure 6.13).
Meanwhile, the hydrogen atoms carried by the enzyme cytochrome oxidase. The
by FAD are introduced in the chain at formation of ATP through the oxidation
carrier two, FAD. Therefore, a pair of of hydrogen atoms is called oxidative
hydrogen atoms carried by FAD makes phosphorylation (Figure 6.13).

4H + 4H + 2H + 3H +
Space
I CoQ III Cyt IV
C Inner
ATP
2e - synthase Mitochondrial
II Membrane
2e -
2H +½ O + 2e →H O Matrix
+

-
2
2
NADH NAD +
2H + FADH FAD + 2H +
2
ADP + Pi ATP + H O
2
Figure 6.13: Electron transport chain 3H +
Generally, in the electron transport chain and uses 10 oxygen atoms (5 molecules
each reduced NAD molecule results in of oxygen). Moreover, each reduced FAD
the production of 3 ATP and the release of molecule (from Kreb’s cycle) results in

hydrogen, which combines with oxygen the production of 2 ATP, hence 2 FAD
to form water. Therefore, the 10 reduced molecules produce 4 ATP. Overall, the
NAD molecules (2 from glycolysis, 2 electron transport chain produces a total
from conversion of pyruvate into Acetyl of 34 ATP molecules from one molecule
CoA and 6 from Kreb’s cycle) results in the of glucose (Figure 6.14).
production of 30 ATP, 10 water molecules

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