ACS BIOCHEMISTRY EXAM | 2026
CORRECT QUESTIONS AND VERIFIED
ANSWERS
Henderson-Hasselbach Equation - Answer~pH = pKa + log ([A-] / [HA])
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.
Salting Out (Purification) - Answer~Changes soluble protein to solid precipitate.
Protein precipitates when the charges on the protein match the charges in the solution.
Size-Exclusion Chromatography - Answer~Separates sample based on size with smaller
molecules eluting later.
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.
Hydrophobic/Reverse Phase Chromatography - Answer~Beads are coated with a
carbon chain. Hydrophobic proteins stick better. Elute with non-H-bonding solvent
(acetonitrile).
Affinity Chromatography - Answer~Attach a ligand that binds a protein to a bead.
Elute with harsh chemicals or similar ligand.
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.
,SDS - Answer~Sodium dodecyl sulfate. Unfolds proteins and gives them uniform
negative charge.
Isoelectric Focusing - Answer~Variation of gel electrophoresis where protein charge
matters. Involves electrodes and pH gradient. Protein stops at their pI when neutral.
FDNB (1-fluoro-2,3-dinitrobenzene) - Answer~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.
DTT (dithiothreitol) - Answer~Reduces disulfide bonds.
Iodoacetate - Answer~Adds carboxymethyl group on free -SH groups. Blocks disulfide
bonding.
Homologs - Answer~Shares 25% identity with another gene
Orthologs - Answer~Similar genes in different organisms
Paralogs - Answer~Similar "paired" genes in the same organism
Ramachandran Plot - Answer~Shows favorable phi-psi angle combinations. 3 main
"wells" for α-helices, ß-sheets, and left-handed α-helices.
Glycine Ramachandran Plot - Answer~Glycine can adopt more angles. (H's for R-
group).
, Proline Ramachandran Plot - Answer~Proline adopts fewer angles. Amino group is
incorporated into a ring.
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.
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-.
ß-sheet - Answer~Either parallel or anti-parallel. Often twisted to increase strength.
Anti-parallel ß-sheet - Answer~Alternating sheet directions (C & N-termini don't line-
up). Has straight H-bonds.
Parallel ß-sheet - Answer~Same sheet directions (C & N-termini line up). Has angled H-
bonds.
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.
Loops - Answer~Not highly structured. Not necessary highly flexible, but can
occasionally move. Very variable in sequence.
Circular Dichroism - Answer~Uses UV light to measure 2° structure. Can be used to
measure destabilization.
Disulfide-bonds - Answer~Bonds between two -SH groups that form between 2° and 3°
structure.
CORRECT QUESTIONS AND VERIFIED
ANSWERS
Henderson-Hasselbach Equation - Answer~pH = pKa + log ([A-] / [HA])
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.
Salting Out (Purification) - Answer~Changes soluble protein to solid precipitate.
Protein precipitates when the charges on the protein match the charges in the solution.
Size-Exclusion Chromatography - Answer~Separates sample based on size with smaller
molecules eluting later.
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.
Hydrophobic/Reverse Phase Chromatography - Answer~Beads are coated with a
carbon chain. Hydrophobic proteins stick better. Elute with non-H-bonding solvent
(acetonitrile).
Affinity Chromatography - Answer~Attach a ligand that binds a protein to a bead.
Elute with harsh chemicals or similar ligand.
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.
,SDS - Answer~Sodium dodecyl sulfate. Unfolds proteins and gives them uniform
negative charge.
Isoelectric Focusing - Answer~Variation of gel electrophoresis where protein charge
matters. Involves electrodes and pH gradient. Protein stops at their pI when neutral.
FDNB (1-fluoro-2,3-dinitrobenzene) - Answer~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.
DTT (dithiothreitol) - Answer~Reduces disulfide bonds.
Iodoacetate - Answer~Adds carboxymethyl group on free -SH groups. Blocks disulfide
bonding.
Homologs - Answer~Shares 25% identity with another gene
Orthologs - Answer~Similar genes in different organisms
Paralogs - Answer~Similar "paired" genes in the same organism
Ramachandran Plot - Answer~Shows favorable phi-psi angle combinations. 3 main
"wells" for α-helices, ß-sheets, and left-handed α-helices.
Glycine Ramachandran Plot - Answer~Glycine can adopt more angles. (H's for R-
group).
, Proline Ramachandran Plot - Answer~Proline adopts fewer angles. Amino group is
incorporated into a ring.
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.
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-.
ß-sheet - Answer~Either parallel or anti-parallel. Often twisted to increase strength.
Anti-parallel ß-sheet - Answer~Alternating sheet directions (C & N-termini don't line-
up). Has straight H-bonds.
Parallel ß-sheet - Answer~Same sheet directions (C & N-termini line up). Has angled H-
bonds.
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.
Loops - Answer~Not highly structured. Not necessary highly flexible, but can
occasionally move. Very variable in sequence.
Circular Dichroism - Answer~Uses UV light to measure 2° structure. Can be used to
measure destabilization.
Disulfide-bonds - Answer~Bonds between two -SH groups that form between 2° and 3°
structure.
