ACS BIOCHEMISTRY Practice EXAM | Actual Questions and Answers
Latest Updated 2024/2025 (Graded A+)
Henderson-Hasselbach Equation - ✔✔pH = pKa + log ([A-] / [HA])
Salting Out (Purification) - ✔✔Changes soluble protein to solid precipitate. Protein precipitates when
the charges on the protein match the charges in the solution.
Size-Exclusion Chromatography - ✔✔Separates sample based on size with smaller molecules eluting
later.
Ion-Exchange Chromatography - ✔✔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 - ✔✔Beads are coated with a carbon chain. Hydrophobic
proteins stick better. Elute with non-H-bonding solvent (acetonitrile).
Affinity Chromatography - ✔✔Attach a ligand that binds a protein to a bead. Elute with harsh chemicals
or similar ligand.
SDS-PAGE - ✔✔Uses SDS. Gel is made from cross-linked polyacrylamide. Separates based off of mass
with smaller molecules moving faster. Visualized with Coomassie blue.
SDS - ✔✔Sodium dodecyl sulfate. Unfolds proteins and gives them uniform negative charge.
Isoelectric Focusing - ✔✔Variation of gel electrophoresis where protein charge matters. Involves
electrodes and pH gradient. Protein stops at their pI when neutral.
Homologs - ✔✔Shares 25% identity with another gene
Orthologs - ✔✔Similar genes in different organisms
, Paralogs - ✔✔Similar "paired" genes in the same organism
Ramachandran Plot - ✔✔Shows favorable phi-psi angle combinations. 3 main "wells" for α-helices, ß-
sheets, and left-handed α-helices.
α-helices - ✔✔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 - ✔✔Formed from added dipole moments of all hydrogen bonds in an α-helix. N-terminus is
δ+ and C-terminus is δ-.
ß-sheet - ✔✔Either parallel or anti-parallel. Often twisted to increase strength.
Anti-parallel ß-sheet - ✔✔Alternating sheet directions (C & N-termini don't line-up). Has straight H-
bonds.
Parallel ß-sheet - ✔✔Same sheet directions (C & N-termini line up). Has angled H-bonds.
ß-turns - ✔✔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 - ✔✔Not highly structured. Not necessary highly flexible, but can occasionally move. Very variable
in sequence.
Circular Dichroism - ✔✔Uses UV light to measure 2° structure. Can be used to measure destabilization.
Disulfide-bonds - ✔✔Bonds between two -SH groups that form between 2° and 3° structure.
ß-mercaptoethanol - ✔✔Breaks disulfide bonds.
Latest Updated 2024/2025 (Graded A+)
Henderson-Hasselbach Equation - ✔✔pH = pKa + log ([A-] / [HA])
Salting Out (Purification) - ✔✔Changes soluble protein to solid precipitate. Protein precipitates when
the charges on the protein match the charges in the solution.
Size-Exclusion Chromatography - ✔✔Separates sample based on size with smaller molecules eluting
later.
Ion-Exchange Chromatography - ✔✔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 - ✔✔Beads are coated with a carbon chain. Hydrophobic
proteins stick better. Elute with non-H-bonding solvent (acetonitrile).
Affinity Chromatography - ✔✔Attach a ligand that binds a protein to a bead. Elute with harsh chemicals
or similar ligand.
SDS-PAGE - ✔✔Uses SDS. Gel is made from cross-linked polyacrylamide. Separates based off of mass
with smaller molecules moving faster. Visualized with Coomassie blue.
SDS - ✔✔Sodium dodecyl sulfate. Unfolds proteins and gives them uniform negative charge.
Isoelectric Focusing - ✔✔Variation of gel electrophoresis where protein charge matters. Involves
electrodes and pH gradient. Protein stops at their pI when neutral.
Homologs - ✔✔Shares 25% identity with another gene
Orthologs - ✔✔Similar genes in different organisms
, Paralogs - ✔✔Similar "paired" genes in the same organism
Ramachandran Plot - ✔✔Shows favorable phi-psi angle combinations. 3 main "wells" for α-helices, ß-
sheets, and left-handed α-helices.
α-helices - ✔✔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 - ✔✔Formed from added dipole moments of all hydrogen bonds in an α-helix. N-terminus is
δ+ and C-terminus is δ-.
ß-sheet - ✔✔Either parallel or anti-parallel. Often twisted to increase strength.
Anti-parallel ß-sheet - ✔✔Alternating sheet directions (C & N-termini don't line-up). Has straight H-
bonds.
Parallel ß-sheet - ✔✔Same sheet directions (C & N-termini line up). Has angled H-bonds.
ß-turns - ✔✔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 - ✔✔Not highly structured. Not necessary highly flexible, but can occasionally move. Very variable
in sequence.
Circular Dichroism - ✔✔Uses UV light to measure 2° structure. Can be used to measure destabilization.
Disulfide-bonds - ✔✔Bonds between two -SH groups that form between 2° and 3° structure.
ß-mercaptoethanol - ✔✔Breaks disulfide bonds.
