It should now be apparent that altering the charge and hydrophobic or hydrophilic nature of amino acids, as well as the length of polypeptide chains, can influence their function. The numerous combinations of amino acids give rise to possibilities that dictate the size and shape of proteins. Small proteins contain 50 to 100 amino acids. The upper limit in size for a protein is —5000 amino acid residues. For example, apolipoprotein B has a single polypeptide chain with a molecular weight of 513 kDa corresponding to about 5000 amino acid residues. In addition, many proteins are made of multiple subunits. In some structural proteins the subunits are often covalently cross-linked into larger complexes that have molecular masses in the millions of daltons. (Note that a dalton is the mass of a hydrogen atom. Protein and peptide molecu-
y/^ NUTRITION INSIGHT
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