Protein Structure: Primary, Secondary, Tertiary, and Quaternary Structures

What is the primary structure of a protein?

The sequence of amino acids in a polypeptide chain, held together by peptide bonds.

What type of bond holds the primary structure of proteins together?

Peptide bonds

What is the secondary structure of a protein?

Folding of the polypeptide chain into structures like alpha helices and beta-pleated sheets, stabilized by hydrogen bonds.

Which types of secondary structures are most common in proteins?

Alpha helices and beta-pleated sheets.

What stabilizes secondary protein structures?

Hydrogen bonds between backbone atoms (not side chains).

What is the tertiary structure of a protein?

The overall 3D shape of a single polypeptide chain, including interactions between side chains (R-groups).

What types of interactions stabilize tertiary structure?

Hydrogen bonds, ionic bonds, disulfide bridges & hydrophobic interactions

What is the quaternary structure of a protein?

The structure formed by two or more polypeptide chains (subunits) coming together.

Do all proteins have quaternary structure?

No, only proteins made of multiple polypeptide subunits have quaternary structure.

Give an example of a protein with quaternary structure.

Hemoglobin

What is a conjugated protein?

A protein that contains a non-protein component in addition to amino acids

What is a non-conjugated protein?

A protein made up only of amino acids and no non-protein components