5

CHAPTER

87

The Chemical

Metabolism

Those of us who need to shed a few pounds tend to blame our weight gain on our
slow metabolism. Metabolismis the collection of biochemical reactions that hap-
pen in our bodies; an example would be the series of reactions that occur when
our digestive system breaks down the food that we eat to energy. All living organ-
isms have a metabolism, including microorganisms. In this chapter you will learn
about the metabolism of the smallest living part of any organism—the cell.

Riding the Metabolism Cycle

The components of a cell, including its plasma membrane and cell wall (and
organelles in eukaryotic organisms), are composed of macromolecules that are
linked together to form these structures. The macromolecules are assembled from
building blocks called precursor metabolites. Think of precursor metabolites as
the bricks that are used to build a wall and the wall as the macromolecule. With

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