Question

Consider the following paragraph.  

Superoxide dismutase is an enzyme that detoxifies a free radical called superoxide.a This radical is responsible for causing injury during reperfusion after a heart attack, and is also thought to play a role in Parkinson’s Disease.b Depending on what organism the protein is found in, it occurs either as a dimer or tetramer of identical subunits.c The subunits are mostly a-helical with some β-sheet near the C-terminus.d A metal binding site for manganese, iron, nickel or copper/zinc is composed of residues from both the N-terminus and the C-terminus.e These residues are: His-26, His-81, Asp-167, His-171.f

Write the letter of the sentence(s) represent primary structure, secondary structure, tertiary structure, and quaternary structure in the above paragraph? You may or may not use all the letters. Explain your choices.

Primary structure =

Secondary structure =

Tertiary structure =

Quaternary structure =

Answer 1

Primary structure =Letter D

A metal binding site for manganese, iron, nickel or copper/zinc is composed of residues from both the N-terminus and the C-terminus

The sequence of amino acids that make up a polypeptide chain is the primary structure .Carboxy terminus or the C terminus is the end of the peptide which has the free carboxyl group and Amino terminus or the N- terminus is the end of the sequence with a free α-amino group.

Secondary structure =Letter C

The subunits are mostly a-helical with some β-sheet near the C-terminus.

Secondary strcuture is segments of proteins forming a three dimensional shape and the two most common structural elements are alpha helices and beta sheets.

Tertiary structure =Letter E

These residues are: His-26, His-81, Asp-167, His-171.

Generally here the protein will bend and twist in such a manner to get maximum stability.Bridges are also formed by oxidation of the sulfhydryl groups on cysteine .This is very important for the stabilization of protein tertiary structure . This also results in a covalent binding between different parts of the protein .

Quaternary structure = The letter B  

Depending on what organism the protein is found in, it occurs either as a dimer or tetramer of identical subunits

The protein is called as a dimer if the product protein is made of two subunits and called as a trimer if it is made up of three subunits and it it four it is called a tetramer .

Quarternary structure is an outcome of multiple folded protein subunits forming a complex.