Biomedical Engineering Reference
In-Depth Information
TABLE 10.8 A summary of Metabolism in Cells
General
Metabolic pathway and/or Metabolic network
Cellular
respiration
Aerobic respiration
Glycolysis
/
pyruvate decarboxylation
/
citric acid
cycle
oxidative phosphorylation (electron transport chain
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ATP
/
synthase)
Anaerobic respiration
Glycolysis
fermentation (ABE, ethanol, lactic acid)
/
Specific paths
Protein metabolism
Protein synthesis and catabolism
Carbohydrate
metabolism
(carbohydrate
catabolism and
anabolism)
Human
Glycolysis
gluconeogenesis
Glycogenolysis
4
glycogenesis
Pentose phosphate pathway;
fructolysis; galactolysis
glycosylation (N-linked,
O-linked)
4
Nonhuman
Photoautotroph or Photosynthesis
(Carbon fixation)
Chemoautotrophs
Pentose metabolism
Lipid metabolism
(lipolysis, lipogenesis)
Fatty acid metabolism
Fatty acid degradation (beta
oxidation); Fatty acid synthesis
Other
Steroid metabolism; sphingolipid
metabolism; eicosanoid
metabolism; ketosis
Amino acid
Amino acid synthesis; urea cycle
Nucleotide metabolism Purine metabolism; nucleotide salvage; pyrimidine metabolism
Other
Metal metabolism (iron metabolism); ethanol metabolism;
hydrocarbon metabolism
oxidized end products for the purpose of generating energy and reducing power. Anabolism
is the biosynthesis of more complex compounds from simpler compounds, usually with the
consumption of energy and reducing power. The key compound to store and release energy
is ATP. Reducing power is stored by NADH or NADPH.
Three of the most important pathways in the cell are (1) the EMP pathway, or glycolysis,
which converts glucose into pyruvate; (2) the TCA cycle or citric acid cycle, which can oxidize
pyruvate through acetyl-CoA into CO 2 and H 2 O; and (3) the PP or HMP pathway, which
converts glucose-6-phosphate into a variety of carbon skeletons (C 3 ,C 4 ,C 5 ,C 6 , and C 7 ),
with glyceraldehyde-3-phosphate (G3P) as the end product. Although all three pathways
can have catabolic and anabolic roles, the EMP pathway and TCA cycle are the primary
means for energy generation, and HMP plays a key role in supplying carbon skeletons
and reducing power for direct use in biosynthesis. In this chapter, we have briefly considered
the relationship of these pathways to amino acid, fatty acid, and polysaccharide biosynthesis.
The conversion of pyruvate to glucose, necessary for polysaccharide biosynthesis when the
carbon source does not have six carbons, is called glucogenesis.
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