#keratin

Cytoskeleton

In epithelial cells, intermediate filaments are mainly composed of:

Epithelial tissues covering skin intestine lung alveoli renal tubules subject to friction stretch requiring robust mechanical buffering and polarity maintenance. Keratin intermediate filaments provide this resilience forming dense cable network 10 nm diameter spanning cytoplasm inserting into desmosomes and hemidesmosomes creating continuous transcellular network distributing tensile forces across sheet preventing cell separation under shear. Expression program tissue specific precisely regulated: basal epidermal keratinocytes keratin 5 and 14 pair suprabasal differentiating keratin 1 and 10 s

Ref: Herrmann et al., Nat Rev Mol Cell Biol 2007 – Keratin main intermediate filament protein in epithelial cells.

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Protein

The central rod domain of keratin consists primarily of:

α-helices 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 α-helices determines its physical properties, biological activity, and interactions with other molecules. The other options (β-sheets, Random coil, and Loop structures) 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 describes the function of keratin intermediate filaments in cells?

Provides tensile strength to epithelial cells is the accurate answer because it correctly identifies the biological function or role described in this question. In Protein, understanding the specific functions of molecules, enzymes, or structures is fundamental. Provides tensile strength to epithelial cells fulfills this particular biological role through its specific structural properties, biochemical activity, or physiological mechanism. The other options (Assists in DNA replication, Acts as an enzyme in metabolic pathways, and Regulates transcription factors) serve different biological func

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

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Protein

Which structural protein is found in reptile scales and bird feathers?

β-Keratin is the correct answer as it accurately identifies the biological location, composition, or distribution described in this question. In Protein, the spatial organization and localization of molecules are critical to their function. β-Keratin is specifically associated with the structure or compartment mentioned because of its unique biochemical properties and physiological role. The other options (α-Keratin, Elastin, and Tropocollagen) 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 keratin, which amino acid is responsible for disulfide bond formation?

Cysteine is the scientifically accurate answer to this question. Within the study of Protein, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Cysteine directly address what is being asked. Among the other options, Glycine, Proline, and Histidine 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 structural proteins is primarily found in hair, nails, and wool?

Keratin is the correct answer as it accurately identifies the biological location, composition, or distribution described in this question. In Protein, the spatial organization and localization of molecules are critical to their function. Keratin is specifically associated with the structure or compartment mentioned because of its unique biochemical properties and physiological role. The other options (Actin, Myosin, and Collagen) 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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