124 Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking
Catalyzed by enzymes, esterification, and hydrol-
ysis in biological systems proceed at much faster
rates than when catalyzed by acids and bases.
WATER INDIGESTION ANDSYNTHESES OF
PROTEINS
The digestion and the formation of many biopoly-
mers (such as proteins and carbohydrates) as well as
the formation and breakdown of lipids and esters
involve reactions very similar to those of esterifica-
tion and hydrolysis.
The digestion of proteins, polymers of amino
acids, starts with chewing, followed by hydrolysis
with the aid of protein-cleaving enzymes (proteases)
throughout the gastrointestinal tract. Then the par-
tially hydrolyzed small peptides and hydrolyzed
individual amino acids are absorbed in the intestine.
Water is a reagent in these hydrolyses (Fig. 5.14).
The deoxyribonucleic acids(DNAs) store the
genetic information, and they direct the synthesis of
messenger ribonucleic acids(mRNAs), which in
turn direct the protein synthesis machinery to make
various proteins for specific body functions and
structures. This is an oversimplified description of
the biological processes that carry out the polymer-
ization of amino acids.
Proteins and amino acids also provide energy
when fully oxidized, but carbohydrates are the major
energy source in normal diets.WATER INDIGESTION ANDSYNTHESIS OF
CARBOHYDRATESOn earth, water is the most abundant inorganic com-
pound, whereas carbohydrates are the most abun-
dant class of organic compounds. Carbohydrates re-
quire water for their synthesis and provide most of
the energy for all life on earth. They are also part of
the glycoproteins and the genetic molecules of DNA.
Carbohydratesare compounds with a deceivingly
simple general formula (CH 2 O)n, n 3, that appears
to be made up of carbon and water, but although
their chemistry fills volumes of thick books and
more, there is still much for carbohydrate chemists
to discover.Figure 5.14.Hydrolysis and peptide-bond formation (polymerization).