ACS Biochemistry 2026 Exam – Comprehensive Question Bank: 200 Questions with Verified Answers and Rationales | Chamberlain University | A+ Rated | Updated for 2026/2027 – Ultimate Biochemistry Study Guide

ACS BIOCHEMISTRY 2026 EXAM –
COMPREHENSIVE QUESTION BANK

200 Questions with Verified Answers and
Rationales

Chamberlain University | A+ Rated |
Updated for 2026/2027


SECTION 1: PROTEIN STRUCTURE & FUNCTION (Questions 1-40)

Q1. Which level of protein structure is determined solely by the sequence of
amino acids?

 Answer: Primary structure

 Rationale: The primary structure is the linear order of amino acids encoded
by DNA. All higher levels of structure (secondary, tertiary, quaternary)
derive from this sequence through the process of protein folding .

Q2. Which two amino acids are most commonly found in beta-turns?

 Answer: Glycine and proline

 Rationale: Glycine has no side chain (flexible), and proline has a rigid ring
that kinks the chain—both accommodate the tight turns required in beta-turn
structures .

,Q3. What type of bond is broken by reducing agents such as DTT or β-
mercaptoethanol?

 Answer: Disulfide bonds (cysteine–cysteine)

 Rationale: DTT reduces –S–S– bonds to two free –SH groups. This is
important for denaturing proteins for electrophoresis and studying protein
structure .

Q4. In a Ramachandran plot, the dark blue regions represent:

 Answer: Sterically allowed phi/psi angles

 Rationale: Not all backbone conformations are possible due to steric clashes
between atoms. Disallowed regions appear empty on the plot. The allowed
regions correspond to α-helix and β-sheet conformations .

Q5. Which interaction is the primary driving force for protein folding?

 Answer: Hydrophobic effect

 Rationale: Nonpolar side chains cluster away from water, increasing water
entropy and driving folding. This is considered the dominant force in protein
folding .

Q6. What does SDS do in SDS-PAGE?

 Answer: Denatures proteins and gives them a uniform negative charge

 Rationale: SDS (sodium dodecyl sulfate) binds to the protein backbone,
coating it with negative charge so separation is by mass only, not by charge
or shape .

Q7. In size-exclusion chromatography, which protein elutes first?

,  Answer: The largest protein

 Rationale: Large proteins cannot enter the porous beads and take a shorter
path through the column, eluting earlier than smaller proteins that get
trapped in the beads .

Q8. What is the isoelectric point (pI)?

 Answer: The pH at which a protein has zero net charge

 Rationale: At pI, proteins aggregate and precipitate. This property is used in
isoelectric focusing for protein separation .

Q9. Which amino acid is absent in alpha-helices because it creates a kink?

 Answer: Proline

 Rationale: Proline's side chain bonds to the backbone nitrogen, preventing
proper hydrogen bonding in helices and introducing a kink .

Q10. What secondary structure is stabilized by hydrogen bonds between
backbone NH and CO groups spaced four residues apart?

 Answer: Alpha-helix (i → i+4 hydrogen bonding)

 Rationale: This repeating hydrogen bonding pattern is the hallmark of the
alpha-helix, with 3.6 residues per turn .

Q11. Which protein structure level involves the arrangement of multiple
polypeptide subunits?

 Answer: Quaternary structure

 Rationale: Examples include hemoglobin (4 subunits), DNA polymerase,
and antibodies which require multiple subunits for function .

, Q12. What is the catalytic triad of chymotrypsin?
k. k. k. k. k. k. k.




 Answer: Serine 195, histidine 57, aspartate 102
k. k. k. k. k. k.




 Rationale: The charge relay system activates serine as a nucleophile.
k. k. k. k. k. k. k. k. k.




Histidine acts as a proton shuttle, and aspartate stabilizes the positively
k. k. k. k. k. k. k. k. k. k. k.




charged histidine .
k. k. k.




Q13. Which amino acid is most commonly involved in the catalytic triad of
k. k. k. k. k. k. k. k. k. k. k. k.




serine proteases?
k. k.




 Answer: Histidine k.




 Rationale: Histidine acts as a proton shuttle during catalysis, accepting a
k. k. k. k. k. k. k. k. k. k.




proton from serine's hydroxyl group and making serine a stronger
k. k. k. k. k. k. k. k. k. k.




nucleophile .
k. k.




Q14. The peptide bond has partial double-bond character primarily because of:
k. k. k. k. k. k. k. k. k. k.




 Answer: Resonance stabilization k. k.




 Rationale: The peptide bond exhibits resonance between the carbonyl
k. k. k. k. k. k. k. k.




carbon and the amide nitrogen, creating partial double-bond character. This
k. k. k. k. k. k. k. k. k. k.




limits rotation and forces the atoms into a planar arrangement .
k. k. k. k. k. k. k. k. k. k. k.




Q15. Which amino acid residue is phosphorylated most often in cell signaling?
k. k. k. k. k. k. k. k. k. k. k.




 Answer: Serine, threonine, or tyrosine
k. k. k. k.




 Rationale: Kinases transferATP's γ-phosphate to the –OH group of these
k. k. k. k. k. k. k. k. k. k.




residues. Serine is most common, followed by threonine and tyrosine .
k. k. k. k. k. k. k. k. k. k. k.




Q16. What is the role of chaperone proteins such as Hsp60 (GroEL)?
k. k. k. k. k. k. k. k. k. k. k.