BIOCHEM 384
BIOC 384 EXAM 2 QUESTIONS AND
SOLUTIONS
Consider the following interaction between a protein and its : [P] + [L] mc021-1.jpg [PL].
If [L] = 5 mM, [P] = 3 mM, and [PL] = 2 mM, what is the dissociation constant? - 7.5
mM
Which of the TWO following statements about x-ray crystallography are true? - Only
crystallized proteins can be analyzed.
The x-ray beam is scattered by the protein sample.
A purified protein shows a single band on a native polyacrylamide gel. The band runs
toward the cathode at pH 7. The figure above shows how the same purified protein runs
on an SDS polyacrylamide gel, with or without dithiothreitol (DTT) added to the sample.
A marker lane is included with sizes of MW standards shown in kDa.
Select the TRUE answers from the statements below. - The protein is a heterooligomeric
complex of three different polypeptide chains.
The protein probably has a high pI value (>7).
Two subunits of the protein are linked by a disulfide bond.
Which of the following is a genomic caretaker protein? - topoisomerase
Which of the following steps happens first in the oxygen binding process? - The O2 binds
to the iron of heme.
Though oxygen only binds to a particular place in the hemoglobin molecule, the oxy- and
deoxy- forms of hemoglobin differ in overall protein conformation. An example of a
structural change that does NOT play a role in translating local binding of oxygen to
BIOCHEM 384
,BIOCHEM 384
global protein conformational change would be the different ______ in the presence and
absence of oxygen binding. - location of the distal histidine
The figure below shows the oxygen binding curve for myoglobin in muscle.
Based on this curve, which of the following is correct? - The lower pO2 in active muscle
leads to release of O2 from myoglobin.
Consider five proteins with the properties shown in the table above and answer the
following four questions. Record your answers and choose the set of correct answers for
questions a --> d.
a) Which protein would elute first from a (+) charged anion exchange column in buffer at
pH 4.0?
b) Which protein would migrate the slowest in an SDS-PAGE gel?
c) Which protein would elute last from a gel filtration chromatography column under
non-denaturing conditions?
d) Which protein would elute last from a (-) charged cation exchange column in buffer at
pH 4.0? - A, E, C, A
In isoelectric focusing, a protein that is physically located in the pH gradient that is below
the pI of the protein would: - migrate toward the cathode
After centrifugation, there is a 10% decrease in activity and a 75% decrease in total
protein. What is purification of the target protein? - 3.6-fold
One of the most difficult steps in X-ray crystallography is: - determining the phases of
diffracted x-rays
Biochemical assays are important in the process of isolating proteins because they: -
uniquely identify one protein
BIOCHEM 384
, BIOCHEM 384
Below is a fractional saturation curve for O2 binding to adult hemoglobin. Assume that
curve Y represents a system at pH 7.4 and with a normal physiological level of 2,3-BPG.
Curve X represents a system that: - has a higher pH with a normal physiological level of
2,3-BPG
Which separation technique exploits the solubility differences of proteins? - salting out
by ammonium sulfate
The figure below shows three proteins that are separated using gel filtration
chromatography. Which protein is the largest? - squares
Which of the following is a positive effector for oxygen binding to hemoglobin? - O2
A polypeptide was digested by trypsin and chymotrypsin. Use the following information
to determine the polypeptide sequence. - LMYKWDERMGFCE
The change in free energy for Solute A concentration across a gradient is calculated to be
-10 kJ/mol. If Solute B is transported against its own concentration gradient using a
secondary active symporter transport mechanism linked to Solute A, what is the
maximum concentration ratio that can be achieved for Solute B in this system? - 50:1
What is the free energy change for transport of a solute from outside the cell to inside the
cell when the concentrations are 5 mM outside and 0.1 mM inside? - -10.1 kJ/mol
If the histidine on the F helix (His F8) that coordinates the heme iron that binds to O2 in
hemoglobin is mutated to an alanine, what effect would be most likely? Choose the ONE
most correct answer. - Oxygen binding would not cause the movement of the F helix,
since the alanine at F8 cannot coordinate the heme iron.
BIOCHEM 384
BIOC 384 EXAM 2 QUESTIONS AND
SOLUTIONS
Consider the following interaction between a protein and its : [P] + [L] mc021-1.jpg [PL].
If [L] = 5 mM, [P] = 3 mM, and [PL] = 2 mM, what is the dissociation constant? - 7.5
mM
Which of the TWO following statements about x-ray crystallography are true? - Only
crystallized proteins can be analyzed.
The x-ray beam is scattered by the protein sample.
A purified protein shows a single band on a native polyacrylamide gel. The band runs
toward the cathode at pH 7. The figure above shows how the same purified protein runs
on an SDS polyacrylamide gel, with or without dithiothreitol (DTT) added to the sample.
A marker lane is included with sizes of MW standards shown in kDa.
Select the TRUE answers from the statements below. - The protein is a heterooligomeric
complex of three different polypeptide chains.
The protein probably has a high pI value (>7).
Two subunits of the protein are linked by a disulfide bond.
Which of the following is a genomic caretaker protein? - topoisomerase
Which of the following steps happens first in the oxygen binding process? - The O2 binds
to the iron of heme.
Though oxygen only binds to a particular place in the hemoglobin molecule, the oxy- and
deoxy- forms of hemoglobin differ in overall protein conformation. An example of a
structural change that does NOT play a role in translating local binding of oxygen to
BIOCHEM 384
,BIOCHEM 384
global protein conformational change would be the different ______ in the presence and
absence of oxygen binding. - location of the distal histidine
The figure below shows the oxygen binding curve for myoglobin in muscle.
Based on this curve, which of the following is correct? - The lower pO2 in active muscle
leads to release of O2 from myoglobin.
Consider five proteins with the properties shown in the table above and answer the
following four questions. Record your answers and choose the set of correct answers for
questions a --> d.
a) Which protein would elute first from a (+) charged anion exchange column in buffer at
pH 4.0?
b) Which protein would migrate the slowest in an SDS-PAGE gel?
c) Which protein would elute last from a gel filtration chromatography column under
non-denaturing conditions?
d) Which protein would elute last from a (-) charged cation exchange column in buffer at
pH 4.0? - A, E, C, A
In isoelectric focusing, a protein that is physically located in the pH gradient that is below
the pI of the protein would: - migrate toward the cathode
After centrifugation, there is a 10% decrease in activity and a 75% decrease in total
protein. What is purification of the target protein? - 3.6-fold
One of the most difficult steps in X-ray crystallography is: - determining the phases of
diffracted x-rays
Biochemical assays are important in the process of isolating proteins because they: -
uniquely identify one protein
BIOCHEM 384
, BIOCHEM 384
Below is a fractional saturation curve for O2 binding to adult hemoglobin. Assume that
curve Y represents a system at pH 7.4 and with a normal physiological level of 2,3-BPG.
Curve X represents a system that: - has a higher pH with a normal physiological level of
2,3-BPG
Which separation technique exploits the solubility differences of proteins? - salting out
by ammonium sulfate
The figure below shows three proteins that are separated using gel filtration
chromatography. Which protein is the largest? - squares
Which of the following is a positive effector for oxygen binding to hemoglobin? - O2
A polypeptide was digested by trypsin and chymotrypsin. Use the following information
to determine the polypeptide sequence. - LMYKWDERMGFCE
The change in free energy for Solute A concentration across a gradient is calculated to be
-10 kJ/mol. If Solute B is transported against its own concentration gradient using a
secondary active symporter transport mechanism linked to Solute A, what is the
maximum concentration ratio that can be achieved for Solute B in this system? - 50:1
What is the free energy change for transport of a solute from outside the cell to inside the
cell when the concentrations are 5 mM outside and 0.1 mM inside? - -10.1 kJ/mol
If the histidine on the F helix (His F8) that coordinates the heme iron that binds to O2 in
hemoglobin is mutated to an alanine, what effect would be most likely? Choose the ONE
most correct answer. - Oxygen binding would not cause the movement of the F helix,
since the alanine at F8 cannot coordinate the heme iron.
BIOCHEM 384
