BIOCHEMISTRY ACS EXAM 2026 ACTUAL
EXAM PAPER QUESTIONS WITH
ANSWERS 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.
◉Collagen ANSWER: - Repeating sequence of Gly-X-Pro. 3 stranded
"coiled coil". Contains gly core.
EXAM PAPER QUESTIONS WITH
ANSWERS 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.
◉Collagen ANSWER: - Repeating sequence of Gly-X-Pro. 3 stranded
"coiled coil". Contains gly core.
