Question

What are the four levels of protein structure? For each level, list what types of bonds and where in the structure each bond is found?

Answer 1

1. Primary structure - consists of covalent peptide bonds between amino acids. This is also known as the sequence of the protein.

2. Secondary structure - consists mostly of hydrogen bonds between local areas of a protein sequence. The hydrogen bonds frequently occur between backbone carbonyl and amino groups and usually form structures like alfa helices and beta sheets.

3. Tertiary structure - this is the overall 3 dimensional structure of the protein, which includes how the beta sheets and alfa helices interact in 3 dimensions. Noncovalent bonds and interactions involving the amino acid side chains are frequently observed - these include hydrophobic interactions, salt bridges, and hydrogen bonds. However, there are covalent bonds in the case of disulfide bridges.

4. Quaternary structure - this involves interactions between different (not covalently connected) polypeptide chains or protein subunits to "build" a multimeric protein. The same types of noncovalent bonds and interactions in tertiary structure are important for quaternary structure, although these interactions are between different polypeptide chains.