C483 Summer 2015
Exam 2
Name ______________________________________________
1. 20 pts Fill in the blanks (2 points each)
A. A plot of velocity as a function of substrate concentration has a _____________ shape in saturation
kinetics unless it is under allosteric regulation.
B. Enzyme efficiency has the parameter _________________, which is a second order rate constant at
low concentration of substrate.
C. Phosphoenolpyruvate is an allosteric effector of phosphofructokinase, and serves as an example of
_______________________ inhibition because it is a product of a reaction further down the pathway.
D. _________________ diffusion of a phospholipid is fast in a lipid bilayer, but ________________
diffusion is slow and requires a flippase.
E. A passive, _______________ transport protein requires one substance to go out of the cell as another
comes into the cell ______________ (with/without) an added energy source.
F. Two examples of second messengers in signal transduction pathways are _______________ and
________________.
G. ___________________________ is a type of signal transduction receptor that catalyzes an
autophosphorylation reaction.
H. When D-glucose cyclizes to form a pyranose, it can form two __________________, which have
different stereochemistry at the hemiacetal carbon. Galactose is the C-4 _________________ of glucose.
I. Of the four major types of biomolecules, ________________ do not provide a major source of calories,
and _________________ do not have a form of long term energy storage.
J. ______________ is a cofactor that transfers 2 electrons at a time, while __________________ is a
cofactor that can transfer either one or 2 electrons.
2. 10 points True or false (1 point each)
A. ______________ An uncompetitive inhibitor increases the apparent KM and lowers the apparent Vmax
of an enzyme catalyzed reaction.
B. ______________ An increase in cholesterol levels would cause the melting point of a lipid bilayer to
increase.
C. ______________ Integral proteins are generally reversibly associated with the cell membrane.
D. ______________ Some gated channels can be opened and closed by membrane potential changes.
E. ______________ A G-protein becomes active in a signal transduction cascade through the hydrolysis
of GTP by its GTPase activity.
F. ______________ Ribose may be considered to be an aldopentose.
G. ______________ Lactose is not digestible by many human adults because they lack the necessary
enzyme.
H. ______________ A reaction with a negative biological standard free energy is spontaneous under all
cellular conditions.
I. ______________ Glyceraldehyde-3-phosphate, alanine, and pyruvate are all 3-carbon intermediates in
metabolic pathways.
J. ______________ When the same hormone causes two different responses in two different tissues
through two separate receptors, it is called cross-talk.
3. (20pts) Short answer (5 points each)
A. In a typical marine organism, the intracellular [Ca+2] = 0.1 M, and the extracellular [Ca=2] = 4 mM.
Assuming a membrane potential of -70 mV, calculate the free energy change for calcium ion entering the
cell at 20 oC using the given equation. In which direction would the calcium ion require active transport?
B. A general schematic of the -andrenergic receptor mediated signal transduction pathway is given
below. On the figure, label three points (using compounds particular to the -andrenergic receptor
mediated signal transduction pathway) at which the signal transduction cascade is turned off, and how it
occurs.
C. Maltose is a disaccharide with an (14) linkage. Hydrolysis leads to two glucose monomers. Draw a
structure for maltose (Haworth or chair.)
D. Fill in any five blanks in this table concerning metabolic fuels in humans:
Biomolecule
carbohydrates
proteins
fats
monomer
Storage polymer
--------------------
Fatty acid
Digestive enzyme
amylase
Storage organ/cell
---------------------Adipose tissue
Problems (10pts each)
4. A Lineweaver-Burk plot of a tyrosinase enzyme is shown below with and without inhibitor.
A. Calculate Vmax for the enzyme with and without inhibitor.
B. Does inhibitor cause the enzyme to apparently bind substrate tighter or looser? Explain why it does so.
C. What type of inhibition is this? _______________________________
5. Glucose is brought into the intestinal cell through secondary active transport through a symport protein
with sodium ion. This process is linked to a Na+/K+ ATPase. Draw a schematic of the intestinal cell with
its transporters, and give a short explanation of how glucose is brought into the cell against its
concentration gradient.
6. A. COX is a key enzyme in the production of prostaglandins, which signal inflammation and pain
responses. Assuming it follows typical Michaelis-Menton kinetics, draw a plot of reaction velocity as a
function of substrate concentration. Draw it to scale assuming a KM value of 0.4 mM and a kcat = 3090 s-1.
(In your experiment, the total enzyme concentration was 90 nM, or 90 x 10-9M.)
B. Write the M-M equation, then use it to derive equations for the velocity of enzyme reaction at very low
[S] and very high [S].
C. Aspirin inhibits COX, which catalyzes a reaction of arachidonic acid, by acetylating a Ser residue on
the enzyme. Draw the reaction that shows how aspirin acetylates the Ser sidechain.
D. Because aspirin is an irreversible inhibitor, it will react with some of the enzyme, lowering the amount
of active enzyme, but not changing the apparent binding ability of the enzyme. Draw the same plot as in
part A for the inhibited enzyme, and explain how it is similar and different than the part A plot.
7. The standard free energy change for the condensation of -D-mannose and inorganic phosphate to
form -D-mannose-6-phosphate is approximately +14 kJ/mol. The standard free energy of ATP
hydrolysis to ADP and inorganic phosphate is approximately -32 kJ/mol.
A. Write the coupled reaction, with full structures of all compounds (You can write “A” for the
nucleobase).
B. What is the standard free energy change for the coupled reaction?
C. What is the G when the [ATP] = 5 mM, [ADP] = 1 mM, and there is approximately 8 times as much
mannose as mannose-6-phosphate? Show all work.
8. Would you expect these four reactions to have a positive, negative, or near zero standard free energy
change? Circle the reaction you would expect to have the most negative value.
ATP   ADP + Pi
2 ADP   AMP + ATP
9. (10pts Case study) The structure of vitamin K is shown below, in its reduced form. This vitamin is an
essential cofactor for an enzyme that activates thrombin, a protease that induces blood coagulation.
(Vitamin K was named after the word “koagulation” by the Danish scientist who discovered it.) In order
for vitamin K to function in its catalytic role, it must be oxidized by the enzyme that activates thrombin.
After thrombin is activated, the enzyme releases the oxidized vitamin K, which is re-reduced by the action
of an enzyme called VKOR. This reduced vitamin K is then bound to the thrombin-cativating enzyme and
re-oxidized while another thrombin is being activated. The full process is called the K cycle.
A. Consider the structural similarity of vitamin K and coenzyme Q, then draw the 2-electron oxidized
form of vitamin K. Would you expect vitamin K to act as a one- or two-electron transfer agent?
B. Based on the amino acid sequence, VKOR is predicted to have 4 transmembrane -helices with the
active site residues in the middle of the helices. Considering the structure of vitamin K, this protein
structure prediction makes sense. Explain.
C. Warfarin is a potent inhibitor of VKOR. It has been used as a rat poison and a human medicine. What
physiological affect would a dose of warfarin have? Why does its dosage have to be monitored so closely
when given to someone as a medicine?
[𝑋]𝑓𝑖𝑛𝑎𝑙
G = RT ln[𝑋]𝑖𝑛𝑖𝑡𝑖𝑎𝑙 + ZF
R = 8.314 J/ mol . K
F = 96,485 J/V . mol