9.3. Carbon and Living Things http://www.ck12.org
fibers (seeFigure9.18). Have you ever eaten raw celery? If you have, then you probably noticed that the stalks
contain long, stringy fibers. The fibers are mostly cellulose.
Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to
trunks and stems. Cellulose also provides needed fiber in the human diet. We can’t digest cellulose, but it helps keep
food wastes moving through the digestive tract.
FIGURE 9.18
Cellulose molecules form large cellulose
fibers.Proteins
Proteinsare biochemical compounds that contain oxygen, nitrogen, and sulfur in addition to carbon and hydrogen.
Protein molecules consist of one or more chains of small molecules called amino acids.
Protein Structure
Amino acids are the "building blocks" of proteins. There are 20 different common amino acids. The structural
formula of the simplest amino acid, called glycine, is shown inFigure9.19. Other amino acids have a similar
structure. The sequence of amino acids and the number of amino acid chains in a protein determine the protein’s
shape. The shape of a protein, in turn, determines its function. Shapes may be very complex. You can learn more
about the structure of proteins at the URL below.