Biochemistry Protein Structure and Function 3

Question 1

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

Accepted Answer

Both B and C

Answer

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.

Question 2

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

Accepted Answer

Hydroxylation of proline and lysine residues

Answer

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.

Question 3

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

Accepted Answer

Antibodies (immunoglobulins)

Answer

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

Question 4

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

Accepted Answer

Rough endoplasmic reticulum

Answer

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.

Question 5

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

Accepted Answer

Lysine

Answer

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.

Biochemistry Practice Test

Biochemistry Practice Test

Biochemistry Protein Structure and Function 3