What do torsion angles describe in polypeptide backbones?

Two torsion angles in the polypeptide chain, also called Ramachandran angles (after the Indian physicist who worked on modeling the interactions in polypeptide chains, Ramachandran, GN, et al., J Mol Biol, 7:95-99) describe the rotations of the polypeptide backbone around the bonds between N-Cα (called Phi, φ) and Cα-C …

Why is the polypeptide backbone flexible?

In a protein, amino acids are linked together by peptide bonds. This dipeptide structure is made of two amino acids. Even though the geometry of the peptide group is fixed, the bonds on either side of the alpha carbons can rotate. This allows flexibility in the peptide backbone.

Can the polypeptide backbone rotate?

and N-H groups must be arranged in space so that the O, H and N atoms lie along a straight bline (Figure 4). Bonds along the peptide backbone rotate so this can happen.

What are the phi and psi angles in a peptide protein?

In this conformation the polypeptide does not form a coil. Instead, it zig-zags in a more extended conformation than the alpha-helix. Amino acid residues in the beta-conformation have negative phi angles and the psi angles are positive. Typical values are phi = -140 degrees and psi = 130 degrees.

What is meant by torsional angle?

: the angle through which a radial section of a body (as a wire or a shaft) deflects from its normal position when the body is subjected to torque.

What is torsional angle in chemistry?

A dihedral angle or torsional angle (symbol: θ) is the angle between two bonds originating from different atoms in a Newman projection. Thus, the angle between C-H1 and C-H4, which is 60º, is a dihedral angle. Geometrically, a dihedral angle is an angle between two intersecting planes.

What is the polypeptide backbone made of?

Proteins (polypeptides) Their backbones are characterized by amide linkages formed by the polymerization between amino and carboxylic acid groups attached to the alpha carbon of each of the twenty amino acids. These amino acid sequences are translated from cellular mRNAs by ribosomes in the cytoplasm of the cell.

What is the backbone of a polypeptide chain?

The backbone of a polypeptide chain is a repeating sequence of three atoms corresponding to the amide nitrogen (N) of the peptide bond, the central tetrahedral carbon (Ca;), and the peptide carbonyl carbon (C) (Fig. 1 ).

Is polypeptide backbone flexible?

Since the backbone of the polypeptide, held together by peptide bonds, is flexible (because of the “rotation about all those bonds”), the chain can bend, twist, and flex into a very large variety of three dimensional shapes.

Which bonds can rotate in a polypeptide backbone?

The partial double bond nature of the peptide bond has profound consequences for protein structure since only the alpha carbons in a protein backbone can potentially rotate freely around their bond axes (bonds 2 and 3, above).

What is torsion angle in chemistry?

A torsion angle ϕ is defined by four consecutive covalently bonded atoms. It is the angle by which atom 4 has to rotate counterclockwise around the axis defined by the rotatable bond (atoms 2 and 3) to be in plane with atoms 1, 2, and 3.