Can you name and describe the four levels of protein structure?

Primary structure - This is the sequence of the amino acids on the polypeptide chain. The amino acids are held together with covalent bonds. When mutations occur, they effect the primary structure of proteins.

Secondary structure - This is the folding of the polypeptide chain into either an alpha helix, a beta sheet. Hydrogen bonds together hold this folded structure.

Tertiary structure – This is the overall 3D shape of the protein and it is produced by hydrophobic and hydrophilic interactions, disulphide bridges (in cysteine), hydrogen bonds and ionic interactions, between the amino acids R groups (side chain). This can either cause the protein to be fibrous or globular. Globular proteins are soluble and an example is haemoglobin, globular proteins have many functions, such as being enzymes. Fibrous proteins often play a role in structure or support, an example is collagen.

Quaternary structure – Many proteins, such as haemoglobin are made up of various polypeptide chains, and these are referred to as protein subunits and they can be the same or different, and the interactions between these subunits are what makes up the overall protein. This structure is stabilised by many of the forces present in tertiary structure, however this time it is between amino acids on different side chains.