ACS BIOCHEMISTRY EXAM UPDATED ACTUAL
QUESTIONS AND CORRECT ANSWERS
Question:
FMOC Chemical Synthesis
Answer:
Used in synthesis of a growing amino acid chain to a polystyrene bead. FMOC is
used as a protecting group on the N-terminus.
Question:
Changes soluble protein to solid precipitate. Protein precipitates when the
charges on the protein match the charges in the solution.
Answer:
Salting Out (Purification)
Question:
Ion-Exchange Chromatography
Answer:
Separates sample based on charge. CM attracts +, DEAE attracts -. May have
repulsion effect on like charges. Salt or acid used to remove stuck proteins.
Question:
Hydrophobic/Reverse Phase Chromatography
Answer:
Beads are coated with a carbon chain. Hydrophobic proteins stick better. Elute
with non-H-bonding solvent (acetonitrile).
Question:
Affinity Chromatography
Answer:
Attach a ligand that binds a protein to a bead. Elute with harsh chemicals or
similar ligand.
Question:
SDS-PAGE
Answer:
Uses SDS. Gel is made from cross-linked polyacrylamide. Separates based off of
mass with smaller molecules moving faster. Visualized with Coomassie blue.
Question:
SDS
Answer:
Sodium dodecyl sulfate. Unfolds proteins and gives them uniform negative
charge.
Question:
, Variation of gel electrophoresis where protein charge matters. Involves
electrodes and pH gradient. Protein stops at their pI when neutral.
Answer:
Isoelectric Focusing
Question:
FDNB reacts with the N-terminus of the protein to produce a 2,4-dinitrophenol
derivative that labels the first residue. Can repeat hydrolysis to determine
sequential amino acids.
Answer:
FDNB (1-fluoro-2,3-dinitrobenzene)
Question:
Ramachandran Plot
Answer:
Shows favorable phi-psi angle combinations. 3 main "wells" for α-helices, ß-sheets,
and left-handed α-helices.
Question:
α-helices
Answer:
Ala is common, Gly & Pro are not very common. Side-chain interactions every 3 or
4 residues. Turns once every 3.6 residues. Distance between backbones is 5.4Å.
Question:
Helix Dipole
Answer:
Formed from added dipole moments of all hydrogen bonds in an α-helix. N-
terminus is δ+ and C-terminus is δ-.
Question:
ß-turns
Answer:
Tight u-turns with specific phi-psi angles. Must have gly at position 3. Proline may
also be at ß-turn because it can have a cis-omega angle.
Question:
Loops
Answer:
Not highly structured. Not necessary highly flexible, but can occasionally move.
Very variable in sequence.
QUESTIONS AND CORRECT ANSWERS
Question:
FMOC Chemical Synthesis
Answer:
Used in synthesis of a growing amino acid chain to a polystyrene bead. FMOC is
used as a protecting group on the N-terminus.
Question:
Changes soluble protein to solid precipitate. Protein precipitates when the
charges on the protein match the charges in the solution.
Answer:
Salting Out (Purification)
Question:
Ion-Exchange Chromatography
Answer:
Separates sample based on charge. CM attracts +, DEAE attracts -. May have
repulsion effect on like charges. Salt or acid used to remove stuck proteins.
Question:
Hydrophobic/Reverse Phase Chromatography
Answer:
Beads are coated with a carbon chain. Hydrophobic proteins stick better. Elute
with non-H-bonding solvent (acetonitrile).
Question:
Affinity Chromatography
Answer:
Attach a ligand that binds a protein to a bead. Elute with harsh chemicals or
similar ligand.
Question:
SDS-PAGE
Answer:
Uses SDS. Gel is made from cross-linked polyacrylamide. Separates based off of
mass with smaller molecules moving faster. Visualized with Coomassie blue.
Question:
SDS
Answer:
Sodium dodecyl sulfate. Unfolds proteins and gives them uniform negative
charge.
Question:
, Variation of gel electrophoresis where protein charge matters. Involves
electrodes and pH gradient. Protein stops at their pI when neutral.
Answer:
Isoelectric Focusing
Question:
FDNB reacts with the N-terminus of the protein to produce a 2,4-dinitrophenol
derivative that labels the first residue. Can repeat hydrolysis to determine
sequential amino acids.
Answer:
FDNB (1-fluoro-2,3-dinitrobenzene)
Question:
Ramachandran Plot
Answer:
Shows favorable phi-psi angle combinations. 3 main "wells" for α-helices, ß-sheets,
and left-handed α-helices.
Question:
α-helices
Answer:
Ala is common, Gly & Pro are not very common. Side-chain interactions every 3 or
4 residues. Turns once every 3.6 residues. Distance between backbones is 5.4Å.
Question:
Helix Dipole
Answer:
Formed from added dipole moments of all hydrogen bonds in an α-helix. N-
terminus is δ+ and C-terminus is δ-.
Question:
ß-turns
Answer:
Tight u-turns with specific phi-psi angles. Must have gly at position 3. Proline may
also be at ß-turn because it can have a cis-omega angle.
Question:
Loops
Answer:
Not highly structured. Not necessary highly flexible, but can occasionally move.
Very variable in sequence.
