ACS Biochemistry Exam Question and Answer
2026 | Comprehensive Review with Detailed
Rationales | Grade A+
• FMOC Chemical Synthesis. CORRECT 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). CORRECT ANSWER: Changes soluble protein to solid
precipitate. Protein precipitates when the charges on the protein match the charges in
the solution.
• Size-Exclusion Chromatography. CORRECT ANSWER: Separates sample based on
size with smaller molecules eluting later.
• Ion-Exchange Chromatography. CORRECT 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. CORRECT ANSWER: Beads are
coated with a carbon chain. Hydrophobic proteins stick better. Elute with non-H-bonding
solvent (acetonitrile).
• Affinity Chromatography. CORRECT ANSWER: Attach a ligand that binds a protein to
a bead. Elute with harsh chemicals or similar ligand.
• SDS-PAGE. CORRECT 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. CORRECT ANSWER: Sodium dodecyl sulfate. Unfolds proteins and gives them
uniform negative charge.
• Isoelectric Focusing. CORRECT 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). CORRECT 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). CORRECT ANSWER: Reduces disulfide bonds.
,• Iodoacetate. CORRECT ANSWER: Adds carboxymethyl group on free -SH groups.
Blocks disulfide bonding.
• Homologs. CORRECT ANSWER: Shares 25% identity with another gene
• Orthologs. CORRECT ANSWER: Similar genes in different organisms
• Paralogs. CORRECT ANSWER: Similar "paired" genes in the same organism
• Ramachandran Plot. CORRECT ANSWER: Shows favorable phi-psi angle
combinations. 3 main "wells" for α-helices, ß-sheets, and left-handed α-helices.
• Glycine Ramachandran Plot. CORRECT ANSWER: Glycine can adopt more angles.
(H's for R-group).
• Proline Ramachandran Plot. CORRECT ANSWER: Proline adopts fewer angles.
Amino group is incorporated into a ring.
• α-helices. CORRECT 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. CORRECT 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. CORRECT ANSWER: Either parallel or anti-parallel. Often twisted to
increase strength.
• Anti-parallel ß-sheet. CORRECT ANSWER: Alternating sheet directions (C & N-termini
don't line-up). Has straight H-bonds.
• Parallel ß-sheet. CORRECT ANSWER: Same sheet directions (C & N-termini line up).
Has angled H-bonds.
• ß-turns. CORRECT 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. CORRECT ANSWER: Not highly structured. Not necessary highly flexible, but
can occasionally move. Very variable in sequence.
• Circular Dichroism. CORRECT ANSWER: Uses UV light to measure 2° structure. Can
be used to measure destabilization.
• Disulfide-bonds. CORRECT ANSWER: Bonds between two -SH groups that form
between 2° and 3° structure.
, • ß-mercaptoethanol. CORRECT ANSWER: Breaks disulfide bonds.
• α-keratin. CORRECT ANSWER: formed from 2 α-helices twisted around each other.
"Coiled coil". Cross-linked by disulfide bonds.
• Collagen. CORRECT ANSWER: Repeating sequence of Gly-X-Pro. 3 stranded "coiled
coil". Contains gly core.
• Myoglobin 4° Structure. CORRECT ANSWER: Symmetric homodimer,
• Hemoglobin 4° Structure. CORRECT ANSWER: Tetramer. Dimer of dimers. α2ß2
tetramer.
• α/ß Protein Folding. CORRECT ANSWER: Less distinct areas of α and ß folding.
• α+ß Protein Folding. CORRECT ANSWER: Two distinct areas of α and ß folding.
• Mechanism of Denaturants. CORRECT ANSWER: Highly soluble, H-binding
molecules. Stabilize protein backbone in water. Allows denatured state to be stabilized.
• Temperature Denaturation of Protein. CORRECT ANSWER: Midpoint of reaction is
Tm.
• Cooperative Protein Folding. CORRECT ANSWER: Folding transition is sharp. More
reversible.
• Folding Funnel. CORRECT ANSWER: Shows 3D version of 2D energy states. Lowest
energy is stable protein. Rough funnel is less cooperative.
• Protein-Protein Interfaces. CORRECT ANSWER: "Core" and "fringe" of the interfaces.
Core is more hydrophobic and is on the inside when interfaced. Fringe is more
hydrophilic.
• π-π Ring Stacking. CORRECT ANSWER: Weird interaction where aromatic rings
stack on each other in positive interaction.
• σ-hole. CORRECT ANSWER: Methyl group has area of diminished electron density in
center; attracts electronegative groups
• Fe Binding of O2. CORRECT ANSWER: Fe2+ binds to O2 reversible. Fe3+ has an
additional + charge and binds to O2 irreversibly. Fe3+ rusts in O2 rich environments.
• Ka for Binding. CORRECT ANSWER: Ka = [PL] / [P][L]
• ϴ-value in Binding. CORRECT ANSWER: ϴ = (bound / total)x100%
ϴ = [L] / ([L] + 1/Ka)
2026 | Comprehensive Review with Detailed
Rationales | Grade A+
• FMOC Chemical Synthesis. CORRECT 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). CORRECT ANSWER: Changes soluble protein to solid
precipitate. Protein precipitates when the charges on the protein match the charges in
the solution.
• Size-Exclusion Chromatography. CORRECT ANSWER: Separates sample based on
size with smaller molecules eluting later.
• Ion-Exchange Chromatography. CORRECT 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. CORRECT ANSWER: Beads are
coated with a carbon chain. Hydrophobic proteins stick better. Elute with non-H-bonding
solvent (acetonitrile).
• Affinity Chromatography. CORRECT ANSWER: Attach a ligand that binds a protein to
a bead. Elute with harsh chemicals or similar ligand.
• SDS-PAGE. CORRECT 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. CORRECT ANSWER: Sodium dodecyl sulfate. Unfolds proteins and gives them
uniform negative charge.
• Isoelectric Focusing. CORRECT 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). CORRECT 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). CORRECT ANSWER: Reduces disulfide bonds.
,• Iodoacetate. CORRECT ANSWER: Adds carboxymethyl group on free -SH groups.
Blocks disulfide bonding.
• Homologs. CORRECT ANSWER: Shares 25% identity with another gene
• Orthologs. CORRECT ANSWER: Similar genes in different organisms
• Paralogs. CORRECT ANSWER: Similar "paired" genes in the same organism
• Ramachandran Plot. CORRECT ANSWER: Shows favorable phi-psi angle
combinations. 3 main "wells" for α-helices, ß-sheets, and left-handed α-helices.
• Glycine Ramachandran Plot. CORRECT ANSWER: Glycine can adopt more angles.
(H's for R-group).
• Proline Ramachandran Plot. CORRECT ANSWER: Proline adopts fewer angles.
Amino group is incorporated into a ring.
• α-helices. CORRECT 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. CORRECT 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. CORRECT ANSWER: Either parallel or anti-parallel. Often twisted to
increase strength.
• Anti-parallel ß-sheet. CORRECT ANSWER: Alternating sheet directions (C & N-termini
don't line-up). Has straight H-bonds.
• Parallel ß-sheet. CORRECT ANSWER: Same sheet directions (C & N-termini line up).
Has angled H-bonds.
• ß-turns. CORRECT 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. CORRECT ANSWER: Not highly structured. Not necessary highly flexible, but
can occasionally move. Very variable in sequence.
• Circular Dichroism. CORRECT ANSWER: Uses UV light to measure 2° structure. Can
be used to measure destabilization.
• Disulfide-bonds. CORRECT ANSWER: Bonds between two -SH groups that form
between 2° and 3° structure.
, • ß-mercaptoethanol. CORRECT ANSWER: Breaks disulfide bonds.
• α-keratin. CORRECT ANSWER: formed from 2 α-helices twisted around each other.
"Coiled coil". Cross-linked by disulfide bonds.
• Collagen. CORRECT ANSWER: Repeating sequence of Gly-X-Pro. 3 stranded "coiled
coil". Contains gly core.
• Myoglobin 4° Structure. CORRECT ANSWER: Symmetric homodimer,
• Hemoglobin 4° Structure. CORRECT ANSWER: Tetramer. Dimer of dimers. α2ß2
tetramer.
• α/ß Protein Folding. CORRECT ANSWER: Less distinct areas of α and ß folding.
• α+ß Protein Folding. CORRECT ANSWER: Two distinct areas of α and ß folding.
• Mechanism of Denaturants. CORRECT ANSWER: Highly soluble, H-binding
molecules. Stabilize protein backbone in water. Allows denatured state to be stabilized.
• Temperature Denaturation of Protein. CORRECT ANSWER: Midpoint of reaction is
Tm.
• Cooperative Protein Folding. CORRECT ANSWER: Folding transition is sharp. More
reversible.
• Folding Funnel. CORRECT ANSWER: Shows 3D version of 2D energy states. Lowest
energy is stable protein. Rough funnel is less cooperative.
• Protein-Protein Interfaces. CORRECT ANSWER: "Core" and "fringe" of the interfaces.
Core is more hydrophobic and is on the inside when interfaced. Fringe is more
hydrophilic.
• π-π Ring Stacking. CORRECT ANSWER: Weird interaction where aromatic rings
stack on each other in positive interaction.
• σ-hole. CORRECT ANSWER: Methyl group has area of diminished electron density in
center; attracts electronegative groups
• Fe Binding of O2. CORRECT ANSWER: Fe2+ binds to O2 reversible. Fe3+ has an
additional + charge and binds to O2 irreversibly. Fe3+ rusts in O2 rich environments.
• Ka for Binding. CORRECT ANSWER: Ka = [PL] / [P][L]
• ϴ-value in Binding. CORRECT ANSWER: ϴ = (bound / total)x100%
ϴ = [L] / ([L] + 1/Ka)
