ACS BIOCHEMISTRY EXAM / 270 + QUESTIONS AND CORRECT VERIFIED ANSWERS BY EXPERTS 2025 LATEST UPDATE GRADED A+.

1. Henderson-Hasselbach Equation ANSWER pH = pKa + log ([A-] / [HA]) 2. FMOC Chemical Synthesis 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) 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 ANSWER Separatessample based on size with smaller molecules eluting later. 5. Ion-Exchange Chromatography ANSWER Separates sample based on charge.CM at- tracts +, DEAE attracts - . May have repulsion effect on like charges. Salt or acid used to remove stuck proteins. 6. Hydrophobic/Reverse Phase Chromatography ANSWER Beads are coated with a car- bon chain. Hydrophobic proteins stick better. Elute with non-H-bonding solvent (acetonitrile). 7. Affinity Chromatography ANSWER Attach a ligand that binds a protein to a bead.Elute with harsh chemicals or similar ligand. 8. SDS-PAGE 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 ANSWER Sodium dodecyl sulfate. Unfolds proteins and gives them uniform negative charge. 10. Isoelectric Focusing 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) 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) ANSWER Reduces disulfide bonds. 13. Iodoacetate ANSWER Adds carboxymethyl group on free -SH groups.Blocks disulfide bonding. 14. Homologs ANSWER Shares 25% identity with another gene 15. Orthologs ANSWER Similar genes in different organisms 16. Paralogs ANSWER Similar "paired" genes in the same organism 17. Ramachandran Plot ANSWER Shows favorable phi-psi angle combinatio "wells" for ±helices, ß-sheets, and left-handed ±h-elices. 18. Glycine Ramachandran Plot ANSWER Glycine can adopt more angles.(H's for R-group). 3 / 27 be used to 19. Proline Ramachandran Plot ANSWER Proline adopts fewer angles. Amino group is incorporated into a ring. 20. ±h-elices ANSWER Ala is common, Gly & Pro are not very common. Side-chain inter- actions every 3 or 4 residues.Turns once every 3.6 residues. Distance between backbones is 5.4Å. 21. Helix Dipole ANSWER Formed from added dipole moments of all hydrogen bonds in an ±h-elix. N-terminus is ´+and C-terminus is ´-. 22. ß-sheet ANSWER Either parallel or anti-parallel. Often twisted to increase strength. 23. Anti-parallel ß-sheet ANSWER Alternating sheet directions(C & N-termini don't line-up). Has straight H-bonds. 24. Parallel ß-sheet ANSWER Same sheet directions (C & N-termini line up). Has angled H-bonds. 25. ß-turns 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. 26. Loops ANSWER Not highly structured.Not necessary highly flexible, but can occasionally move. Very variable in sequence. 27. Circular Dichroism ANSWER Uses UV light to measure 2° structure.Can measure destabilization. 28. Disulfide-bonds ANSWER Bonds between two -SH groups that form between 2° and 3° structure. 29. ß-mercaptoethanol ANSWER Breaks disulfide bonds. 30. ±k-eratin ANSWER formed from 2 ±h-elices twisted around each other. "Coiled coil". Cross-linked by disulfide bonds. 31. Collagen ANSWER Repeating sequence of Gly-X-Pro. 3 stranded "coiled coil".Contains gly core. 32. Myoglobin 4° Structure ANSWER Symmetric homodimer, 33. Hemoglobin 4° Structure ANSWER Tetramer. Dimer of dimers. ± 2ß 2 tetramer. 34. ±ß/ Protein Folding ANSWER Less distinct areas of ±and ß folding. 35. ±+ß Protein Folding ANSWER Two distinct areas of ±and ß folding. 36. Mechanism of Denaturants ANSWER Highly soluble, H-binding molecules. Stabilize protein backbone in water. Allows denatured state to be stabilized. 37. Temperature Denaturation of Protein ANSWER Midpoint of reaction is Tm. 38. Cooperative Protein Folding ANSWER Folding transition is sharp. More reversible. 39. Folding Funnel ANSWER Shows 3D version of 2D energy states.Lowest energy isstable protein. Rough funnel is less cooperative. 4 / 27 40. Protein-Protein Interfaces ANSWER "Core" and "fringe" of the interfaces.Core is more hydrophobic and is on the inside when interfaced. Fringe is more hydrophilic. 5 / 27 hat can be 41. ÀR-Ài n g Stacking ANSWER Weird interaction where aromatic ringsstack on each other in positive interaction. 42. Ãh-ole ANSWER Methyl group has area of diminished electron density in center; attracts electronegative groups 43. FeBinding of O2 ANSWER Fe2+ bindsto O2 reversible.Fe3+ has an additional + charge and binds to O2 irreversibly. Fe3+ rusts in O2 rich environments. 44. Ka for Binding ANSWER Ka = [PL] / [P][L] 45. ôv-alue inBinding ANSWER ô =b(ound / total)x100% ô =L[] / ([L] + 1/Ka) 46. Kd for binding ANSWER Kd = [L] when 50% bound to protein. Kd = 1/Ka 47. High-Spin Fe ANSWER Electrons are "spread out" and result in larger atom. 48. Low-Spin Fe ANSWER Electrons are less "spread out" and are compacted by electron rich porphyrin ring. 49. T-State ANSWER Heme is in high-spin state. H2O is bound to heme. 50. R-State ANSWER Heme is in low-spin state. O2 is bound to heme. 51. O2 Binding Event ANSWER O2 binds to T-state and changes the heme to R-state. Causes a 0.4Å movement of the iron. 52. Hemoglobin Binding Curve ANSWER 4 subunits present in hemoglobin t either T or R - state. Cooperative binding leads to a sigmoidal curve. 53. Binding Cooperativity ANSWER When one subunit of hemoglobin changes from T to R-state the other sites are more likely to change to R-state as well. Leads to sigmoidal graph. 54. Homotropic Regulation of Binding ANSWER Where a regulatory molecule is also the enzyme's substrate. 55. Heterotro