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ACS Biochemistry Comps EXAM – Questions With Solutions
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ACS Biochemistry Comps EXAM – Questions With Solutions
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ACS Biochemistry Comps EXAM – Questions WithSolutions
Ion-Exchange Chromatography Right Ans - 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 Right Ans - Beads are coated
with a carbon chain. Hydrophobic proteins stick better. Elute with non-H-
bonding solvent (acetonitrile).
Affinity Chromatography Right Ans - Attach a ligand that binds a protein to
a bead. Elute with harsh chemicals or similar ligand.
SDS-PAGE Right Ans - Uses SDS. Gel is made from cross-linked
polyacrylamide. Separates based off of mass with smaller molecules moving
faster. Visualized with Coomassie blue.
SDS Right Ans - Sodium dodecyl sulfate. Unfolds proteins and gives them
uniform negative charge.
Isoelectric Focusing Right Ans - 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) Right Ans - FDNB reacts with the N-
terminus of the protein to produce a 2,4-dinitrophenol derivative that labels
the first residue and stabilizes it for subsequent break of its peptide bond. Can
repeat hydrolysis to determine sequential amino acids. Main reagent for
Sanger sequencing.
DTT (dithiothreitol) Right Ans - Reduces disulfide bonds.
Iodoacetate Right Ans - Adds carboxymethyl group on free -SH groups.
Blocks disulfide bonding.
Homologs Right Ans - Shares 25% identity with another gene
, Orthologs Right Ans - Similar genes in different organisms
Paralogs Right Ans - Similar "paired" genes in the same organism
Ramachandran Plot Right Ans - Shows favorable phi-psi angle
combinations. 3 main "wells" for α-helices, ß-sheets, and left-handed α-
helices.
α-helices Right Ans - 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 Right Ans - Formed from added dipole moments of all
hydrogen bonds in an α-helix. N-terminus is δ+ and C-terminus is δ-.
ß-sheet Right Ans - Either parallel or anti-parallel. Often twisted to
increase strength.
Anti-parallel ß-sheet Right Ans - Alternating sheet directions (C & N-
termini don't line-up). Has straight H-bonds.
Parallel ß-sheet Right Ans - Same sheet directions (C & N-termini line up).
Has angled H-bonds.
ß-turns Right Ans - 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 Right Ans - Not highly structured. Not necessary highly flexible, but
can occasionally move. Very variable in sequence.
Disulfide-bonds Right Ans - Bonds between two -SH groups that form
between 2° and 3° structure.
ß-mercaptoethanol Right Ans - Breaks disulfide bonds.
α-keratin Right Ans - formed from 2 α-helices twisted around each other.
"Coiled coil". Cross-linked by disulfide bonds.
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