BIOCHEMISTRY ACS TEST PAPER 2026
ACTUAL QUESTIONS AND SOLUTIONS
GRADED A+
◉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.
◉ß-mercaptoethanol .ANSWER:-Breaks disulfide bonds.
◉α-keratin .ANSWER:-formed from 2 α-helices twisted around each
other. "Coiled coil". Cross-linked by disulfide bonds.
ACTUAL QUESTIONS AND SOLUTIONS
GRADED A+
◉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.
◉ß-mercaptoethanol .ANSWER:-Breaks disulfide bonds.
◉α-keratin .ANSWER:-formed from 2 α-helices twisted around each
other. "Coiled coil". Cross-linked by disulfide bonds.
