Protein

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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Protein

Which amino acid is NOT involved in the formation of disulfide bonds?

Cysteine is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Protein Structure, the other options (Methionine, Homocysteine, and Selenocysteine) are all valid and well-established concepts. Cysteine 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: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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Protein

Which of the following statements about β-sheets is correct?

They always have evenly spaced hydrogen bonds is the scientifically accurate answer to this question. Within the study of Protein Structure, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of They always have evenly spaced hydrogen bonds directly address what is being asked. Among the other options, Parallel β-sheets are more stable than antiparallel, They contain side chains pointing alternately above and below the sheet, and They are never involved in domain structures 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: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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Protein

The function of fibronectin is primarily:

Electron transport is the accurate answer because it correctly identifies the biological function or role described in this question. In Protein Structure, understanding the specific functions of molecules, enzymes, or structures is fundamental. Electron transport fulfills this particular biological role through its specific structural properties, biochemical activity, or physiological mechanism. The other options (Oxygen storage, Extracellular matrix binding, and Hydroxylation of xenobiotics) serve different biological functions or are associated with other processes, pathways, or structural roles within the cell or organism.

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

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Protein

The term “holoprotein” refers to:

A protein with its prosthetic group accurately defines or describes the concept asked in this question. Within Protein Structure, precise definitions and terminology are essential for clear scientific communication. The other options (A protein without its prosthetic group, A protein composed entirely of β-sheets, and A protein composed entirely of α-helices) either describe related but distinct concepts, use incorrect terminology, or confuse similar-sounding terms that have different scientific meanings. A thorough understanding of exact definitions helps distinguish between closely related biological concepts and is crucial for competitive examinations.

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

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Protein

The prosthetic group in hemoproteins consists of:

Heme accurately describes the structural composition or molecular organization asked about in this question. In Protein Structure, knowledge of molecular structure is directly linked to understanding biological function. The specific arrangement of chemical components in Heme determines its physical properties, biological activity, and interactions with other molecules. The other options (Carbohydrates, Lipids, and Metal ions) describe different structural arrangements, incorrect stoichiometry, or compositions of different biological molecules.

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

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Protein

Which of the following statements about domains is INCORRECT?

Small proteins usually have multiple domains is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Protein Structure, the other options (A domain is an independently folded tertiary structure, A domain is a structural and functional unit, and Domains are evolutionary conserved structures) are all valid and well-established concepts. Small proteins usually have multiple domains 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: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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Protein

Which motif is frequently involved in DNA binding?

Helix-turn-helix is the accurate answer because it correctly identifies the biological function or role described in this question. In Protein Structure, understanding the specific functions of molecules, enzymes, or structures is fundamental. Helix-turn-helix fulfills this particular biological role through its specific structural properties, biochemical activity, or physiological mechanism. The other options (Greek-key motif, β-hairpin, and Rossmann fold) serve different biological functions or are associated with other processes, pathways, or structural roles within the cell or organism.

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

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Protein

Which amino acid is commonly found in β-hairpins?

Proline is the correct answer as it accurately identifies the biological location, composition, or distribution described in this question. In Protein Structure, the spatial organization and localization of molecules are critical to their function. Proline is specifically associated with the structure or compartment mentioned because of its unique biochemical properties and physiological role. The other options (Alanine, Isoleucine, and Serine) are primarily associated with different cellular compartments, tissues, or structural contexts.

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

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Protein

In a 300 amino acid-long protein, the approximate length of the anti-parallel β-sheet conformation is:

1050 Ã… is the scientifically accurate answer to this question. Within the study of Protein Structure, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of 1050 Ã… directly address what is being asked. Among the other options, 420 Ã…, 450 Ã…, and 840 Ã… 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: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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Protein

A protein with 10 cysteine residues can form a maximum of how many disulfide bonds?

45 is the scientifically accurate answer to this question. Within the study of Protein Structure, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of 45 directly address what is being asked. Among the other options, 10, 28, and 36 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: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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Protein

Which of the following interactions is NOT involved in stabilizing tertiary protein structure?

Peptide bonds is the correct choice because it does not accurately describe or belong to the category addressed in this question. In the context of Protein Structure, the other options (Hydrophobic interactions, Hydrogen bonds, and Ionic interactions) are all valid and well-established concepts. Peptide bonds 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: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 4

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