1) Proteins are made up of polypeptide chains formed from amino acid residues joined by peptide bonds. 2) Proteins fold into complex 3D structures determined by various intramolecular forces including covalent bonds, hydrogen bonds, hydrophobic interactions, and van der Waals forces. 3) The number and type of amino acid residues in a protein can be determined through end group analysis using techniques like Dansyl chloride labeling of N-termini and carboxypeptidase digestion of C-termini.