Final answer:
Proteins are made of alpha amino acids because they form more stable and predictable structures which are essential for proper protein function. The side chains determine the protein's folding and function, and the evolutionary prevalence indicates that alpha amino acids are fundamental to life processes. Beta or gamma amino acids could disrupt protein stability and are not favored by evolution.
Step-by-step explanation:
Proteins are essential macromolecules in biological systems, made up of amino acids linked by peptide bonds. The amino acids used in protein synthesis are alpha amino acids. The term alpha amino acids refers to the specific structure where the amino group is attached to the alpha (α) carbon next to the carboxyl group. This specific configuration is key to protein structure and function for several reasons.
Stability and Simplicity
Alpha amino acids provide greater stability for the protein structure due to their capacity to form more predictable and uniform secondary structures like alpha-helices and beta-sheets. Beta or gamma amino acids have additional carbons between the amino and carboxyl groups which could disrupt this regularity, leading to less stable structures. The simpler structure of alpha amino acids makes it easier for enzymes to synthesize proteins efficiently and correctly.
Folding and Function
The unique side chains (R groups) of alpha amino acids determine the chemical nature and, consequently, the three-dimensional folding of the protein. This specificity in folding is crucial to how proteins function and interact with other molecules. Amino acids such as valine, methionine, and alanine have nonpolar side chains, while others like serine, threonine, and cysteine have polar side chains. The nature of these side chains influences the final protein structure and its biological activity.
Evolutionary Prevalence
The prevalence of alpha amino acids in proteins across all living organisms suggests an evolutionary advantage. This uniformity amongst life forms indicates that the use of alpha amino acids is fundamental to the proper functioning of proteins necessary for life processes. While two additional amino acids, selenocysteine and pyrolyzing, have been found in proteins, they are rare exceptions to the common structures.