Test: Tertiary Structure of Protein - MCAT MCQ

Tertiary structure of a protein describes the folding of its secondary structural elements and specifies the position of every atom in a protein, including those of side chains. Moreover, the tertiary structure of a protein consists of secondary structural elements that join to form motifs and domains.

Arg is most likely to be present on the surface of a protein because it is a polar residue. Generally, polar residues reside on the surface of a protein. Val, leu, and Ile are non-polar residues, hence, they are not likely to be present on the surface of a protein.

Glu is the odd one out. Glu is a charged, polar amino acid and is, therefore, most likely to be present on the surface of a protein. Phe, Met, and leu are non-polar, thus, likely to be present in the interior of the protein.

The option containing Val, Met, and Phe is the correct option. Val, Met, and Phe are all non-polar residues, hence, likely to be present in the interior of the protein. Arg, Asp, and Lys are polar residues.

PDB is a structural database. PDB stands for Protein Data Bank. It is the repository of structural information. CATH, SCOP, and VAST are not structural databases, on the contrary, they are structural classification algorithms. PDB archive is the single worldwide repository of information about the 3D structures of large biological molecules, including proteins and nucleic acids.

It is the protein’s structure that is highly conserved among the homologous proteins over the evolutionary time. It is the protein 3D structure that is responsible for its biological activity and not its sequence.

X-ray crystallography is a technique where in electron density maps are obtained. Thus, the term “electron density maps” is related to X-ray crystallography. Other techniques mentioned do not involve electron density maps.

Hydrogen atom is not visible in the electron density maps of X-ray crystallography. The reason behind this is the low electron density of the hydrogen atom. Hydrogen contains a minimum of one electron.

Val is most likely to be present in the interior of a protein because it is a non-polar residue. Generally, non-polar residues reside in the interior of the protein. Arg, His, and Asp are polar residues, hence, they are not likely to be present in the interior of a protein.

The option containing Arg, Asp, and Lys is the correct option. Due to the polar nature of Asp, Arg, and Lys, they are most likely to be present on the surface of a protein. Leu, Val, and Met are non-polar residues.