#phi psi angles

Ramachandran plot

Which dihedral angle is NOT associated with the peptide backbone?

ω (omega) is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Peptide and Ramachandran plo, the other options (ϕ (phi), ψ (psi), and χ (chi)) are all valid and well-established concepts. ω (omega) is either unrelated to the topic, describes a different biological process, or represents a common misconception. Questions framed as 'which is NOT' require students to identify the exception among otherwise correct statements, demanding comprehensive knowledge of the topic rather than recognition of a single fact.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Ramachandran plot

Why are all the theoretical combinations of phi (ϕ) and psi (ψ) not possible?

Two atoms cannot occupy the same space is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Peptide and Ramachandran plo, the other options (Peptide bond restricts angles, β-sheets and α-helices limit space, and Tertiary structure folding restricts movement) are all valid and well-established concepts. Two atoms cannot occupy the same space is either unrelated to the topic, describes a different biological process, or represents a common misconception. Questions framed as 'which is NOT' require students to identify the exception among otherwise correct statements, demanding comprehensive knowledge of the topic rather than recognition of a single fact.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Ramachandran plot

Which statement about the Ramachandran plot is correct?

It identifies sterically allowed dihedral angles correctly identifies the graphical representation, mathematical relationship, or plot parameter described in this question. In Peptide and Ramachandran plo, graphical analysis transforms complex kinetic or biological data into linear relationships that allow precise determination of key parameters. The specific feature described by It identifies sterically allowed dihedral angles is derived from the mathematical transformation of the underlying equation and has a defined physical meaning. The other options (It helps in sequence determination of peptides, It predicts the function of a peptide, and It measures peptide bond cleavage) represent different parameters, intercepts, or slopes from either the same or different analytical methods.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Ramachandran plot

What prevents the complete randomization of phi (ϕ) and psi (ψ) angles in peptides?

Steric hindrance is the scientifically accurate answer to this question. Within the study of Peptide and Ramachandran plo, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Steric hindrance directly address what is being asked. Among the other options, Hydrogen bonding, Hydrophobic interactions, and Peptide bond hydrolysis do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Campbell Biology, Urry et al., 12th Ed.

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Protein

The dihedral angles (ϕ and ψ) in a Type-II β-turn are approximately:

ϕ = -60°, ψ = +120° is the accurate classification or categorization for the organism, molecule, or concept described in this question. In Protein Structure, proper classification is based on shared characteristics including morphological, biochemical, genetic, and evolutionary criteria. ϕ = -60°, ψ = +120° meets the specific diagnostic features and defining criteria that distinguish it from related groups. The other options (ϕ = -60°, ψ = -30°, ϕ = -90°, ψ = 0°, and ϕ = +80°, ψ = 0°) belong to different taxonomic groups, represent different classification levels, or possess distinct characteristics that exclude them from this category.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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