Henderson-Hasselbach Equation
Ans- pH = pKa + log ([A-] / [HA])
Salting Out (Purification)
Ans- Changes soluble protein to solid precipitate. Protein precipitates when
the charges on the protein match the charges in the solution.
Size-Exclusion Chromatography
Ans- Separates sample based on s...
ACS BIOCHEMISTRY EXAM Questions and Answers Henderson -Hasselbach Equation Ans- pH = pKa + log ([A -] / [HA]) Salting Out (Purification) Ans- Changes soluble protein to solid precipitate. Protein precipitates when the charges on the protein match the charges in the solution. Size-Exclusion Chromatography Ans- Separates sample based on size with smaller molecules eluting later. Ion-Exchange C hromatography 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 Ans- Beads are coated with a carbon ch ain. Hydrophobic proteins stick better. Elute with non -H-bonding solvent (acetonitrile). Affinity Chromatography Ans- Attach a ligand that binds a protein to a bead. Elute with harsh chemicals or similar ligand. SDS-PAGE Ans- Uses SDS. Gel is made fr om cross -linked polyacrylamide. Separates based off of mass with smaller molecules moving faster. Visualized with Coomassie blue. SDS Ans- Sodium dodecyl sulfate. Unfolds proteins and gives them uniform negative charge. Isoelectric Focusing Ans- Variation of gel electrophoresis where protein charge matters. Involves electrodes and pH gradient. Protein stops at their pI when neutral. Iodoacetate Ans- Adds carboxymethyl group on free -SH groups. Blocks disulfide bonding. Homologs Ans- Shares 25% identity with another gene Orthologs Ans- Similar genes in different organisms Ramachandran Plot Ans- Shows favorable phi -psi angle combinations. 3 main "wells" for α -helices, ß-sheets, and left -handed α -helices. α-helices Ans- Ala is c ommon, 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 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 Ans- Either parallel or anti -parallel. Often twisted to increase strength. Anti-parallel ß -sheet Ans- Alternating sheet directions (C & N -termini don't line -up). Has straight H-bonds.
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