Which of the following levels of protein structure corresponds to the formation of the globular protein distinguished by the hydrophobic and hydrophilic properties of the subunits?
A primary
B secondary
C tertiary
D quaternary
E None of the answers are correct
The correct answer and explanation is:
The correct answer is C. Tertiary.
Explanation:
Proteins have four distinct levels of structure: primary, secondary, tertiary, and quaternary. The level of protein structure that corresponds to the formation of the globular protein with hydrophobic and hydrophilic properties of the subunits is tertiary structure.
The tertiary structure refers to the overall 3D shape of a protein, formed by the folding of the polypeptide chain. This folding occurs due to interactions between the side chains (R-groups) of the amino acids that make up the protein. These interactions include:
- Hydrophobic interactions: Nonpolar side chains tend to cluster in the interior of the protein, away from the surrounding water, because they are repelled by water molecules.
- Hydrophilic interactions: Polar or charged side chains tend to be on the surface of the protein, where they interact with the aqueous environment.
The specific folding pattern of the tertiary structure allows the protein to adopt a functional shape, which is essential for its biological activity. In globular proteins, which are typically soluble in water, this folding results in a compact, spherical shape, with hydrophobic amino acids buried inside and hydrophilic amino acids on the exterior, interacting with water.
The primary structure refers to the linear sequence of amino acids, while the secondary structure involves the local folding of the polypeptide into structures such as alpha helices or beta sheets, primarily stabilized by hydrogen bonds. The quaternary structure describes the assembly of multiple polypeptide chains (subunits) into a functional protein, which is not the case here.
Thus, the tertiary structure is the correct level where the hydrophobic and hydrophilic interactions contribute to the formation of a globular protein.