Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
When amino acids bind together, they form a long chain called a polypeptide . A protein consists of one or more polypeptide chains. A protein may have up to four levels of structure. The lowest level, a protein’s primary structure, is its sequence of amino acids. Higher levels of protein structure are described in Figure below . The complex structures of different proteins give them unique properties, which they need to carry out their various jobs in living organisms. You can learn more about protein structure by watching the animation at the following link: http://www. stolaf. edu/people/giannini/flashanimat/proteins/protein%20structure. swf .


Question: When amino acids bind together, they form a long chain called what, which is an essential component of protein?
polypeptide
Polypeptide.