ACS BIOCHEMISTRY ACTUAL
EXAM WITH COMPLETE
QUESTIONS AND CORRECT
DETAILED ANSWERS (100%
VERIFIED ANSWERS) |ALREADY
GRADED A+| ||PROFESSOR
VERIFIED|| ||BRANDNEW!!!||
2026/2027
A researcher prepares a buffer with pKa = 6.1 and
wants a pH of 7.1. Which ratio of conjugate base to
acid is required?
A. 1:1
B. 10:1
C. 0.1:1
D. 2:1
Correct Answer: B
Rationale: The Henderson–Hasselbalch equation
states pH = pKa + log([A−]/[HA]). When pH is one
unit above pKa, the log term must equal 1.
,Therefore, [A−]/[HA] = 10. This reflects a tenfold
excess of conjugate base over acid, which is
necessary to shift the buffer system toward a higher
pH. This concept is frequently tested because it
connects logarithmic relationships to biochemical
buffering systems, especially in physiological
contexts such as blood pH regulation.
A protein precipitates when ammonium sulfate is
added. What is the primary mechanism?
A. Increased hydrogen bonding
B. Decreased protein charge
C. Competition for water molecules
D. Increased ionic bonding
Correct Answer: C
Rationale: Salting out occurs because salt ions
compete with proteins for water molecules, reducing
solvation of the protein. As hydration shells
collapse, hydrophobic interactions dominate and
proteins aggregate and precipitate. This is not due to
charge neutralization directly but rather reduced
,solvent availability. This concept is high-yield in
purification techniques and protein chemistry.
Which chromatography technique would best
separate proteins solely based on size?
A. Ion-exchange chromatography
B. Affinity chromatography
C. Size-exclusion chromatography
D. Reverse-phase chromatography
Correct Answer: C
Rationale: Size-exclusion chromatography separates
molecules based on their hydrodynamic radius.
Larger molecules elute first because they cannot
enter the pores of the beads, while smaller molecules
are delayed. This technique does not depend on
charge or binding affinity, making it ideal for size-
based separation. Understanding elution order is
commonly tested.
A protein binds strongly to a DEAE column. What is
its likely charge at that pH?
, A. Positive
B. Neutral
C. Negative
D. Amphipathic
Correct Answer: C
Rationale: DEAE is positively charged and binds
negatively charged proteins. Therefore, proteins that
bind strongly must carry a net negative charge at the
working pH. This reflects ion-exchange principles
where opposite charges attract. Students must
recognize specific resin properties.
Which reagent breaks disulfide bonds?
A. Iodoacetate
B. DTT
C. SDS
D. FDNB
Correct Answer: B
Rationale: Dithiothreitol (DTT) reduces disulfide
bonds by donating electrons, converting them into
free thiol groups. This is critical for protein
EXAM WITH COMPLETE
QUESTIONS AND CORRECT
DETAILED ANSWERS (100%
VERIFIED ANSWERS) |ALREADY
GRADED A+| ||PROFESSOR
VERIFIED|| ||BRANDNEW!!!||
2026/2027
A researcher prepares a buffer with pKa = 6.1 and
wants a pH of 7.1. Which ratio of conjugate base to
acid is required?
A. 1:1
B. 10:1
C. 0.1:1
D. 2:1
Correct Answer: B
Rationale: The Henderson–Hasselbalch equation
states pH = pKa + log([A−]/[HA]). When pH is one
unit above pKa, the log term must equal 1.
,Therefore, [A−]/[HA] = 10. This reflects a tenfold
excess of conjugate base over acid, which is
necessary to shift the buffer system toward a higher
pH. This concept is frequently tested because it
connects logarithmic relationships to biochemical
buffering systems, especially in physiological
contexts such as blood pH regulation.
A protein precipitates when ammonium sulfate is
added. What is the primary mechanism?
A. Increased hydrogen bonding
B. Decreased protein charge
C. Competition for water molecules
D. Increased ionic bonding
Correct Answer: C
Rationale: Salting out occurs because salt ions
compete with proteins for water molecules, reducing
solvation of the protein. As hydration shells
collapse, hydrophobic interactions dominate and
proteins aggregate and precipitate. This is not due to
charge neutralization directly but rather reduced
,solvent availability. This concept is high-yield in
purification techniques and protein chemistry.
Which chromatography technique would best
separate proteins solely based on size?
A. Ion-exchange chromatography
B. Affinity chromatography
C. Size-exclusion chromatography
D. Reverse-phase chromatography
Correct Answer: C
Rationale: Size-exclusion chromatography separates
molecules based on their hydrodynamic radius.
Larger molecules elute first because they cannot
enter the pores of the beads, while smaller molecules
are delayed. This technique does not depend on
charge or binding affinity, making it ideal for size-
based separation. Understanding elution order is
commonly tested.
A protein binds strongly to a DEAE column. What is
its likely charge at that pH?
, A. Positive
B. Neutral
C. Negative
D. Amphipathic
Correct Answer: C
Rationale: DEAE is positively charged and binds
negatively charged proteins. Therefore, proteins that
bind strongly must carry a net negative charge at the
working pH. This reflects ion-exchange principles
where opposite charges attract. Students must
recognize specific resin properties.
Which reagent breaks disulfide bonds?
A. Iodoacetate
B. DTT
C. SDS
D. FDNB
Correct Answer: B
Rationale: Dithiothreitol (DTT) reduces disulfide
bonds by donating electrons, converting them into
free thiol groups. This is critical for protein
