ACS BIOCHEMISTRY EXAM WITH LATEST
QUESTIONS AND ANSWERS___ well updated
1. Henderson-Hasselbach Equation (Correct Answer) - ✅ pH = pKa + log ([A-] / [HA])
2. 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.
3. 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.
4. Size-Exclusion Chromatography (Correct Answer) - ✅ Separates sample based on
size with smaller molecules eluting later.
5. 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.
6. Hydrophobic/Reverse Phase Chromatography (Correct Answer) - ✅ Beads are
coated with a carbon chain. Hydrophobic proteins stick better. Elute with non-H-bonding
solvent (acetonitrile).
,7. Affinity Chromatography (Correct Answer) - ✅ Attach a ligand that binds a protein
to a bead. Elute with harsh chemicals or similar ligand.
8. 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.
9. SDS (Correct Answer) - ✅ Sodium dodecyl sulfate. Unfolds proteins and gives them
uniform negative charge.
10. Isoelectric Focusing (Correct Answer) - ✅ Variation of gel electrophoresis where
protein charge matters. Involves electrodes and pH gradient. Protein stops at their pI
when neutral.
11. 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.
12. DTT (dithiothreitol) (Correct Answer) - ✅ Reduces disulfide bonds.
13. Iodoacetate (Correct Answer) - ✅ Adds carboxymethyl group on free -SH groups.
Blocks disulfide bonding.
14. 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.
QUESTIONS AND ANSWERS___ well updated
1. Henderson-Hasselbach Equation (Correct Answer) - ✅ pH = pKa + log ([A-] / [HA])
2. 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.
3. 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.
4. Size-Exclusion Chromatography (Correct Answer) - ✅ Separates sample based on
size with smaller molecules eluting later.
5. 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.
6. Hydrophobic/Reverse Phase Chromatography (Correct Answer) - ✅ Beads are
coated with a carbon chain. Hydrophobic proteins stick better. Elute with non-H-bonding
solvent (acetonitrile).
,7. Affinity Chromatography (Correct Answer) - ✅ Attach a ligand that binds a protein
to a bead. Elute with harsh chemicals or similar ligand.
8. 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.
9. SDS (Correct Answer) - ✅ Sodium dodecyl sulfate. Unfolds proteins and gives them
uniform negative charge.
10. Isoelectric Focusing (Correct Answer) - ✅ Variation of gel electrophoresis where
protein charge matters. Involves electrodes and pH gradient. Protein stops at their pI
when neutral.
11. 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.
12. DTT (dithiothreitol) (Correct Answer) - ✅ Reduces disulfide bonds.
13. Iodoacetate (Correct Answer) - ✅ Adds carboxymethyl group on free -SH groups.
Blocks disulfide bonding.
14. 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.
