Download Sample exam 1

Chemistry 256
Sample exam 1 (Lipids, amino acid metabolism, membrane transport)
You may take up to 24 hours to complete the exam. including lengthy breaks to sleep or
attend work or classes. Recommended time is 80 minutes; there are 50 points possible.
Please record the actual amount of time you took on the exam so that I can get an idea of
how long it took the class on average. The exam is semi-open book (textbook but no
other books) and websites (you may use the textbook website but no other sites), open
notes, class handouts, case studies and exercises. You may attach additional sheets if
needed for your answers, but clearly label what problem(s) they are for. There is to be no
collaboration.
Multiple choice; please circle your selection.
1. Which of the following molecules does not occur in at least one pathway of the
conversion of aspartate into oxaloacetate?
a. fumarate
b. malate
c. asparagine
d. argininosuccinate
e. malate
2. Which one of the following enzymes releases a precursor for prostaglandin synthesis
from phospholipids?
a. adipose cell lipase
b. phospholipase D
c. phospholipase C
d. phospholipase A1
e. phospholipase A2
3. Which one of the following can be consumed directly to produce significant amounts
of metabolic energy in the brain but not in the liver?
a. palmitoleic acid
b. glucose
c. acetoacetate
d. albumin
e. carnitine
4. The enzyme that acts on ketone bodies to convert them into a form that can be broken
down into acetyl CoA is present in brain, but not in liver. What type of reaction is
catalyzed by this enzyme?
a. Oxidation.
b. Dehydration.
c. Transfer of CoA.
d. Hydroxylation.
e. Decarboxylation.
5. Which one of the following choices is not used to produce acetyl CoA in humans?
a. a 15:0 fatty acid.
b. Palmitate.
c. Acetoacetate.
d. Cholesterol.
e. Actually, all of the choices can be used to produce acetyl CoA in humans.
6. The pyrrole rings of heme each contain nitrogen atoms. What molecule provides that
nitrogen during the synthesis of heme in liver cells?
a. Carbamoyl phosphate.
b. Cobalamin.
c. Glycine.
d. Succinyl CoA.
e. Valine.
7. Which of the following statements is true?
a. Glucose can cross the lipid bilayer freely by simple diffusion.
b. Benzene requires a transporter to cross the lipid bilayer.
c. Ions such as Cl– require a channel to cross the lipid bilayer.
d. Water does not require a channel to cross the membrane, although urea does.
e. All of the statements are true.
Essay questions: Answer all of the following in paragraph form or drawings, as requested.
8. How many ATP molecules will the 18:2 fatty acids make in mammals? Give a
reasonably detailed accounting to justify your answers. Assume that 3,2-enoyl-CoA
isomerase acts only when energetically advantageous for the organism – in other words,
problem 3 in figure 20-15 is avoided).
9. (3 points) Qualitatively sketch the rate of passive transport uptake of a
substance (call it “M”) versus its external (extra-cellular) concentration by:
a. diffusion through the membrane
b. a shuttle carrier
c. a channel former
10. E. coli glutamine synthatase is covalently modified by adenylylation (the addition of
an AMP group) to specfic Tyr residues. More than one Tyr can be adenylylated on the
enzyme, and the number of adenylylated Tyr residues is called the degree of
adenylylation, symbolized n. Assuming that n is some non-zero value to start with,
qualitatively describe and justify how n will change if:
a. [ATP] increases.
b. [α-ketoglutarate]/[glutamine] decreases.
c. [Pi] decreases.
Make sure to use the word “adenylyltransferase” in your answers. Hint: figure 21-29 on
page 744 may be helpful.
11. In the cleavage of argininosuccinate into fumarate and arginine in the urea cycle
(reaction 4 in figure 21-9), the argininosuccinase has a guanidino group at the active
site. Explain how this takes part in the mechanism of the cleavage. The guanidino group
is shown below:
12. Explain the formation of the following compounds:
14CO
2,
, and
by metabolic pathways starting with 14C-labeled lauric acid:
Show enough steps to make clear why the labeled carbons end up where they do.
13. Gastric juice has a pH of 1.5 and is produced by pumping HCl from blood plasma
(pH 7.4) into the stomach.
a. Calculate the free energy required to concentrate the H+ in 1 L of gastric juice at 37°C.
For this problem, you can ignore the effects of the transmembrane electrical potential
difference.
b. At these physiological conditions, ATP hydrolysis has a free energy change of – 58
kJ/mol. How many moles of ATP must be hydrolyzed to generate the gastric juice in
part a?