2. Introduction
The citric acid cycle — also known as the
tricarboxylic acid cycle (TCA cycle), the Krebs
cycle — is a series of enzyme-catalysed chemical
reactions, which is of central importance in all
living cells that use oxygen as part of cellular
respiration.
11. Net reaction of citric acid cycle
• The reactions of the
citric acid cycle
oxidize acetyl-CoA’s
acetyl group to two
molecules of carbon
dioxide.
• During the reaction
cycle, electrons are
transferred from
acetyl-CoA to
electron carriers.
12. • Once an electron carrier accepts an electron, it is referred to
as “reduced.”
• Ultimately, reduced electron carriers participate in
downstream reaction pathways that generate ATP
13.
14.
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16.
17. • In the case of higher eukaryotes, a
cell most commonly acquires
glucose in two ways—by breaking
down complex carbohydrates into
simple sugars and by mobilizing
glucose from glycogen, the body’s
storage system for glucose.
• In the cytosol, glucose is broken
down to two, 3-carbon pyruvate
during glycolysis.
• Pyruvate is transported across the
mitochondrial membrane where
it is broken down to a 2-carbon
compound called acetyl-CoA plus
carbon dioxide.
18. • Remaining carbon skeleton is broken down to acetyl-CoA or
to pyruvate, which is then converted to acetyl-CoA.
• Alternatively, a citric acid cycle intermediate such as α-
ketoglutarate may result
• An amino acid consists of an
amino and a carboxyl group at
opposite ends, plus an attached
side chain.
• Amino group of an amino acid is
removed in a deamination
reaction
19. • Fatty acids - carboxylic acid with a long, hydrocarbon tail
• Palmitate is an example of a sixteen-carbon fatty acid
20. • When a cell’s metabolic needs increase, free fatty acids enter
the mitochondrion where the degradative reactions called β
oxidation ensue.
• A fatty acid shortened by two carbon atoms plus a free acetyl-
CoA molecule results from each round of b oxidation.