The branch of the U.S. government that is composed of the president and all the individuals, agencies, and departments that report to the president, and that is responsible for administering and enforcing the laws that Congress passes.
Proteins are biological polymers composed of amino acids. Amino acids, linked together by peptide bonds, form a polypeptide chain. One or more polypeptide chains twisted into a 3-D shape form a protein. Proteins have complex shapes that include various folds, loops, and curves.
In this type of structure a hydrogen bond forms between an amino acid and one four amino acids further along the chain. In a perfect alpha-helix, therefore, every peptide bond is hydrogen-bonded to two other peptide bonds in the chain length, but this is rarely the case in natural proteins.