Glutamine r


Amino acids with positively charged 'R' groups


I Arginine r r r

C=NH2+ NHa

Amino acids with negatively charged 'R' groups

j*12 Glutamic acid ch2

Aspartic acid C=o

Figure 6.2 The twenty amino acids used to make the proteins of life. The "R" or side groups can be neutral, or big and bulky, or charged. The sequence of amino acids in a protein will then determine the final shape.

Some proteins contain just a few amino acids linked together, while others contain hundreds of amino acids. Scientists often refer to the links of amino acids in the following manner.

  • Peptides are 2 to 10 amino acids including dipeptides, tripeptides, etc.
  • Polypeptides are 11 to 100 amino acids.
  • Proteins are over 100 amino acids.

Other scientists will describe protein size based on the weight of the protein molecule (molecular weight) and sometimes use the term daltons as a unit of weight. When we discuss proteins in this book we will refer to protein size and design only if its helps us understand a protein's unique function.

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