Final answer:
Proteins can have a practically infinite number of combinations and structures due to the diversity of amino acid sequences and the resulting unique three-dimensional shapes. The number of proteins that can be synthesized using 20 commonly found amino acids is enormously large, akin to the possibilities of creating sentences using letters from the English alphabet.
Step-by-step explanation:
Proteins, which have up to four levels of structure, can have a practically infinite number of possible combinations and structures. The number of proteins that can be synthesized using 20 amino acids commonly found in proteins is enormously large, similar to the possibilities of creating sentences using letters from 26 alphabets in the English language. The diversity of proteins is the result of the different sequences and arrangements of amino acids, which give rise to unique three-dimensional shapes and chemical properties.