- | Page
ACS BIOCHEMISTRY EXA M
QUESTIONS AND CORREC T
SOLUTIONS
Question :Henderson-Hasselbach Equation
CORRECT ANSWER :pH = pKa + log ([A-] / [HA])
Question :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.
Question :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.
Question :Size-Exclusion Chromatography
CORRECT ANSWER :Separates sample based on size
with smaller molecules eluting later.
- | Page
Question :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.
Question :Hydrophobic/Reverse Phase Chromatography
CORRECT ANSWER :Beads are coated with a carbon
chain. Hydrophobic proteins stick better. Elute with non- H-bonding solvent (acetonitrile).
Question :Affinity Chromatography
CORRECT ANSWER :Attach a ligand that binds a
protein to a bead. Elute with harsh chemicals or similar ligand.
Question :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.
- | Page
Question :SDS
CORRECT ANSWER :Sodium dodecyl sulfate. Unfolds
proteins and gives them uniform negative charge.
Question :Isoelectric Focusing
CORRECT ANSWER :Variation of gel electrophoresis
where protein charge matters. Involves electrodes and pH gradient. Protein stops at their pI when neutral.
Question :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.
Question :DTT (dithiothreitol)
CORRECT ANSWER :Reduces disulfide bonds.
Question :Iodoacetate
- | Page
CORRECT ANSWER :Adds carboxymethyl group on
free -SH groups. Blocks disulfide bonding.
Question :Homologs
CORRECT ANSWER :Shares 25% identity with another
gene
Question :Orthologs
CORRECT ANSWER :Similar genes in different
organisms
Question :Paralogs
CORRECT ANSWER :Similar "paired" genes in the
same organism
Question :Ramachandran Plot
CORRECT ANSWER :Shows favorable phi-psi angle
combinations. 3 main "wells" for α-helices, ß-sheets, and left-handed α-helices.