MCQs

The C-peptide connects the A and B chains in proinsulin and is removed to form mature insulin.

Resonance restricts rotation around the peptide bond, making these six atoms coplanar.

Domains are independently folded regions within a single polypeptide and are part of tertiary structure.

The Val-6 substitution creates a hydrophobic patch on deoxyhemoglobin, leading to polymerization and sickling of red blood cells.

The oxidizing environment of the endoplasmic reticulum promotes the formation of disulfide bonds in secreted and membrane proteins.

Protein function depends on proper folding into the native three-dimensional structure.

The heme prosthetic group contains Fe²⁺, which reversibly binds oxygen.

β-sheets are classified according to the orientation of adjacent strands.

Histidine's pKa is close to physiological pH, making it ideal for acid-base catalysis.

Chaperones bind exposed hydrophobic regions of unfolded proteins, preventing aggregation and promoting correct folding.

Heat disrupts weak interactions but usually leaves the covalent peptide backbone intact.

Collagen contains the repeating sequence Gly-X-Y. Glycine occurs every third residue, allowing tight packing of the triple helix.

Quaternary structure exists only in proteins composed of more than one polypeptide chain, such as hemoglobin.

The hydrophobic effect causes non-polar side chains to cluster in the interior, minimizing contact with water and stabilizing the folded structure.

In an α-helix, the carbonyl oxygen of residue i hydrogen bonds with the amide hydrogen of residue i+4, producing the stable helical conformation.

Secondary structures are stabilized by hydrogen bonding between peptide backbone atoms rather than side chains.

Basic amino acids have side chains that accept protons. Lysine contains an ε-amino group that is positively charged at physiological pH.

Peptide bond formation is a dehydration synthesis. The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another, releasing a water molecule (H₂O) and forming a covalent amide linkage (-CO-NH-).

Primary structure is the linear, genetically determined sequence of amino acids in a polypeptide chain, held together by covalent peptide bonds. This sequence dictates all higher levels of protein structure.