Proteins Are Polymer Chains Composed of Amino Acid Monomers

Proteins Are Polymer Chains Composed of Amino Acid Monomers 

Proteins, which play a key role in nearly all biological processes, are polymers of amino acids. Enzymes, the catalysts of biochemical reactions, are mostly proteins. Proteins also facilitate a wide range of other functions, such as the transport and storage of vital substances, coordinated motion, mechanical support, and protection against diseases. 

The human body contains an estimated 100,000 different kinds of proteins, each of which has a specific physiological function. As we will see in this section, the chemical composition and structure of these complex natural polymers are the basis of their specificity. 

Proteins have high molar masses SjmsgpQ m P0tF(x)( ha ]l 6ez l yet the percent composition by mass orae aements in proteins is remarkably constant carbon, approximately 53 percent hydrogen, 7 percent oxygen, 23 percent nitrogen, 16 percent and sulfur, 1 percent. 

The basic structural units of proteins are amino acids. An amino acid is a compound that contains at least one amino group (—NH2) and at least one carboxyl group (—COOH)  

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Polymers are, by definition, molecules composed by a large number of small chemical units, the monomers. Above, we have discussed A- and B-homopolymers, assuming that all A-polymers are composed of the same single A-monomer, and B-polymers by another specific B-monomer. Such chemical equality is often the situation in synthetic polymers, as for example polyethylene purely composed of -CH2- ethylene monomers. Many natural polymers, on the other hand, are composed of several different monomers example of these include proteins, which are polymeric chains composed of different amino acids such polymers are termed copolymers. 

A polymer is a long-chain molecule composed of a large number of repeated subunits called monomers. These subunits can be as simple as a CHj group, as is the case for polyethylene, or the subunit can be a much more complex collection of atoms. Even molecules as complex as proteins are polymers, long chains of different amino acid subunits. The definition of a polymer can therefore be applied to an extremely wide variety of molecular structures, so the bulk properties of different polymers are diverse. Some examples are shown in Figure 4.2. 

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