Protein Structure and Function Flashcards

Collagen's unique triple-helix structure is stabilized primarily by which amino acid's repeated occurrence?

Answer: Both B and C

Collagen's Gly-X-Y repeat sequence requires glycine (smallest residue) at every third position, and proline/hydroxyproline at X and Y positions to stabilize the helix with hydrogen bonds.

Vitamin C (ascorbate) is required for collagen synthesis because it is needed for:

Answer: Hydroxylation of proline and lysine residues

Ascorbate is a cofactor for prolyl and lysyl hydroxylases, which add hydroxyl groups to proline and lysine residues essential for helix stability and cross-linking.

Which class of proteins contains immunoglobulin-fold domains and is central to adaptive immunity?

Answer: Antibodies (immunoglobulins)

Antibodies are glycoproteins with characteristic immunoglobulin folds consisting of beta-sandwich domains, forming variable regions that bind specific antigens.

A signal peptide on a newly synthesized protein directs it to which cellular location for processing?

Answer: Rough endoplasmic reticulum

Signal peptides are N-terminal hydrophobic sequences recognized by signal recognition particle (SRP), which directs the ribosome to the rough ER for co-translational insertion.

Ubiquitin-mediated proteasomal degradation requires that ubiquitin chains be attached to which amino acid residue of the target protein?

Answer: Lysine

Ubiquitin is attached via an isopeptide bond to lysine residues on target proteins; a chain of at least four ubiquitin molecules targets the protein to the 26S proteasome.

The Bohr effect refers to which property of hemoglobin?

Answer: Decreased O₂ affinity at lower pH and higher CO₂

The Bohr effect describes hemoglobin's decreased oxygen affinity in acidic, high-CO₂ environments (active tissues), facilitating O₂ release where it is needed most.