3.36 Biochemical Compound Classification
A:Glucose is synthesized in photosynthesis.
Virtually all living things use glucose for energy, but glucose is just one of many examples of biochemical compounds
that are found in most or all living things. In fact the similarity in biochemical compounds between living things
provides some of the best evidence for the evolution of species from common ancestors. A classic example is the
biochemical compound called cytochrome c. It is found in all living organisms because it performs essential life
functions. Only slight variations in the molecule exist between closely related species, as you can see in theFigure
3.68. The molecule is identical in humans and their closest relatives, the chimpanzees. And even between humans
and the single-celled tetrahymena (pictured in theFigure3.68), the cytochrome c molecule is nearly 50 percent the
same.
FIGURE 3.68
Structure of Biochemical Molecules
All biochemical molecules contain hydrogen and oxygen as well as carbon. They may also contain nitrogen,
phosphorus, and/or sulfur. Almost all biochemical compounds are polymers. Polymers are large molecules that
consist of many smaller, repeating molecules, called monomers. Glucose is a monomer of biochemical compounds
called starches. In starches and all other biochemical polymers, monomers are joined together by covalent bonds, in
which atoms share pairs of valence electrons.
Size of Biochemical Molecules
Most biochemical molecules are macromolecules. The prefixmacro-means “large,” and many biochemical molecules
are very large indeed. They may contain thousands of monomer molecules. The largest known biochemical molecule
is called titin. It plays an important role in muscle contraction. The human form of the molecule contains more than
34,000 monomers. Its chemical formula is C 169723 H 270464 N 45688 O 52243 S 912. Its chemical name contains almost
190,000 letters, and it has been called the longest word in any language. Its chemical name is read rapidly in the
video at the following URL—and the video lasts more than 8 minutes!