Page 143 - Demo 1

Anaerobic respiraon refers to the type of respiraon that takes place in the
absence of oxygen. This form of respiraon is carried out in bacteria, yeasts,
some prokaryotes, and muscle cells. In this process, energy, carbon dioxide,
and lacc acid or alcohol are produced by the breakdown of glucose molecules.
It uses electron acceptors other than oxygen, and involves the processes of
glycolysis and fermentaon.

FERMENTATION

In the absence of oxygen, aerobic metabolism cannot take place, and cells
must depend exclusively on glycolysis to produce ATP. Fermentaon is the
anaerobic breakdown of glucose that generates two ATP per glucose molecule.
Fermentaon and cellular respiraon begin in the same way with glycolysis. In
fermentaon, however, the pyruvate made in glycolysis does not connue
through oxidaon and the Krebs cycle and the electron transport chain does not
run.

1. Lactic acid fermentation

During fermentaon in animal cells, the pyruvate formed by glycolysis
accepts two hydrogen atoms and is reduced to lactate (deprotonated
form of lacc acid). In muscle cells, for example, the enzyme lactate
dehydrogenase transfers a hydrogen atom from NADH back to the
pyruvate produced by glycolysis. This reacon converts pyruvate into
lactate, recycles NAD from NADH, and keeps glycolysis going in order to
+
produce ATP. Lacc acid produced in muscle cells is transported through
the bloodstream to the liver, where it is converted back to pyruvate and
processed normally in the remaining reacons of cellular respiraon.

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