ACS Biochemistry Exam 2025/2026 – Questions and Answers -Guaranteed
Pass (Latest Update), Exams of Chemistry
Henderson-Hasselbach Equation - ANSWERpH = pKa + log ([A-] / [HA])
FMOC Chemical Synthesis - ANSWERUsed 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) - ANSWERChanges soluble protein to solid
precipitate. Protein precipitates when the charges on the protein match the
charges in the solution.
Size-Exclusion Chromatography - ANSWERSeparates sample based on size
with smaller molecules eluting later.
Ion-Exchange Chromatography - ANSWERSeparates 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 - ANSWERBeads are coated
with a carbon chain. Hydrophobic proteins stick better. Elute with non-H-
bonding solvent (acetonitrile).
,Affinity Chromatography - ANSWERAttach a ligand that binds a protein to a
bead. Elute with harsh chemicals or similar ligand.
SDS-PAGE - ANSWERUses SDS. Gel is made from cross-linked polyacrylamide.
Separates based off of mass with smaller molecules moving faster. Visualized
with Coomassie blue.
SDS - ANSWERSodium dodecyl sulfate. Unfolds proteins and gives them
uniform negative charge.
Isoelectric Focusing - ANSWERVariation 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) - ANSWERFDNB 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) - ANSWERReduces disulfide bonds.
Iodoacetate - ANSWERAdds carboxymethyl group on free -SH groups. Blocks
disulfide bonding.
Homologs - ANSWERShares 25% identity with another gene
Orthologs - ANSWERSimilar genes in different organisms
,Paralogs - ANSWERSimilar "paired" genes in the same organism
Ramachandran Plot - ANSWERShows favorable phi-psi angle combinations. 3
main "wells" for α-helices, ß-sheets, and left-handed α-helices.
Glycine Ramachandran Plot - ANSWERGlycine can adopt more angles. (H's for
R-group).
Proline Ramachandran Plot - ANSWERProline adopts fewer angles. Amino
group is incorporated into a ring.
α-helices - ANSWERAla 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 - ANSWERFormed from added dipole moments of all hydrogen
bonds in an α-helix. N-terminus is δ+ and C-terminus is δ-.
ß-sheet - ANSWEREither parallel or anti-parallel. Often twisted to increase
strength.
Anti-parallel ß-sheet - ANSWERAlternating sheet directions (C & N-termini
don't line-up). Has straight H-bonds.
Parallel ß-sheet - ANSWERSame sheet directions (C & N-termini line up). Has
angled H-bonds.
, ß-turns - ANSWERTight 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 - ANSWERNot highly structured. Not necessary highly flexible, but can
occasionally move. Very variable in sequence.
Circular Dichroism - ANSWERUses UV light to measure 2° structure. Can be
used to measure destabilization.
Disulfide-bonds - ANSWERBonds between two -SH groups that form between
2° and 3° structure.
ß-mercaptoethanol - ANSWERBreaks disulfide bonds.
α-keratin - ANSWERformed from 2 α-helices twisted around each other.
"Coiled coil". Cross-linked by disulfide bonds.
Collagen - ANSWERRepeating sequence of Gly-X-Pro. 3 stranded "coiled coil".
Contains gly core.
Myoglobin 4° Structure - ANSWERSymmetric homodimer,
Hemoglobin 4° Structure - ANSWERTetramer. Dimer of dimers. α2ß2
tetramer.
α/ß Protein Folding - ANSWERLess distinct areas of α and ß folding.
Pass (Latest Update), Exams of Chemistry
Henderson-Hasselbach Equation - ANSWERpH = pKa + log ([A-] / [HA])
FMOC Chemical Synthesis - ANSWERUsed 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) - ANSWERChanges soluble protein to solid
precipitate. Protein precipitates when the charges on the protein match the
charges in the solution.
Size-Exclusion Chromatography - ANSWERSeparates sample based on size
with smaller molecules eluting later.
Ion-Exchange Chromatography - ANSWERSeparates 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 - ANSWERBeads are coated
with a carbon chain. Hydrophobic proteins stick better. Elute with non-H-
bonding solvent (acetonitrile).
,Affinity Chromatography - ANSWERAttach a ligand that binds a protein to a
bead. Elute with harsh chemicals or similar ligand.
SDS-PAGE - ANSWERUses SDS. Gel is made from cross-linked polyacrylamide.
Separates based off of mass with smaller molecules moving faster. Visualized
with Coomassie blue.
SDS - ANSWERSodium dodecyl sulfate. Unfolds proteins and gives them
uniform negative charge.
Isoelectric Focusing - ANSWERVariation 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) - ANSWERFDNB 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) - ANSWERReduces disulfide bonds.
Iodoacetate - ANSWERAdds carboxymethyl group on free -SH groups. Blocks
disulfide bonding.
Homologs - ANSWERShares 25% identity with another gene
Orthologs - ANSWERSimilar genes in different organisms
,Paralogs - ANSWERSimilar "paired" genes in the same organism
Ramachandran Plot - ANSWERShows favorable phi-psi angle combinations. 3
main "wells" for α-helices, ß-sheets, and left-handed α-helices.
Glycine Ramachandran Plot - ANSWERGlycine can adopt more angles. (H's for
R-group).
Proline Ramachandran Plot - ANSWERProline adopts fewer angles. Amino
group is incorporated into a ring.
α-helices - ANSWERAla 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 - ANSWERFormed from added dipole moments of all hydrogen
bonds in an α-helix. N-terminus is δ+ and C-terminus is δ-.
ß-sheet - ANSWEREither parallel or anti-parallel. Often twisted to increase
strength.
Anti-parallel ß-sheet - ANSWERAlternating sheet directions (C & N-termini
don't line-up). Has straight H-bonds.
Parallel ß-sheet - ANSWERSame sheet directions (C & N-termini line up). Has
angled H-bonds.
, ß-turns - ANSWERTight 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 - ANSWERNot highly structured. Not necessary highly flexible, but can
occasionally move. Very variable in sequence.
Circular Dichroism - ANSWERUses UV light to measure 2° structure. Can be
used to measure destabilization.
Disulfide-bonds - ANSWERBonds between two -SH groups that form between
2° and 3° structure.
ß-mercaptoethanol - ANSWERBreaks disulfide bonds.
α-keratin - ANSWERformed from 2 α-helices twisted around each other.
"Coiled coil". Cross-linked by disulfide bonds.
Collagen - ANSWERRepeating sequence of Gly-X-Pro. 3 stranded "coiled coil".
Contains gly core.
Myoglobin 4° Structure - ANSWERSymmetric homodimer,
Hemoglobin 4° Structure - ANSWERTetramer. Dimer of dimers. α2ß2
tetramer.
α/ß Protein Folding - ANSWERLess distinct areas of α and ß folding.
