CHEM-643 Intermediary Metabolism
Name/Group ________________________
Friday, 20 November 2009
Individual and Group Quiz on Amino Acid Metabolism Case Study Problem,
“Plants vs Animals in the Dining Hall”
Select the best answer. Please note that true statements are not necessarily correct answers or
explanations. Tables 1-3 from the case study problem are reproduced on the last page, which you can tear
off for use. Your total score will be distributed 60% individual score plus 40% group score.
____ 14. By now you should have a conceptual overview of amino acid metabolism and the
Steele (1952) and Aqvist (1951) experiments that might look something like the figure
below.
Dietary
Proteins
15
N Amino Acid
14
C Sucrose
Common
Intermediates
Intestinal
uptake
de novo
synthesis
Free
Amino Acids
Protein
synthesis
Cellular
Proteins
sample
1. Separate Protein
2. Hydrolyze Protein
3. Separate Amino Acids
Protein
degradation
[-NH3+]
4. Determine
14
C or
15
N/mg
for each amino acid
Catabolism
Urea
CO2 + H2O
The amount of 14C and 15N in an amino acid will depend on the relative importance of
the processes represented by arrows. Consider the results presented in Tables 1 and 3 for
threonine. From these results one can conclude that:
A. Threonine synthesis and degradation are much greater than for other amino acids.
B. Threonine synthesis and degradation are much less than for other amino acids.
C. Threonine synthesis is much greater, but degradation is much less than for other
amino acids.
D. Threonine synthesis is much less but, degradation is much greater than for other
amino acids.
____ 15. Consider the above diagram again. If adult animals were fed a diet high in protein, what
would you expect would happen to the rates of various processes indicated?
A. Cellular protein synthesis would increase, but protein degradation would decrease.
B. Cellular protein synthesis and protein degradation would increase.
C. Amino acid synthesis would decrease, but amino acid catabolism would increase.
D. Amino acid synthesis and catabolism would increase.
____ 16. Seeds typically provide a rich source of protein; however, compared to protein in meat,
seed proteins are often unbalanced with respect to one or more amino acids that are in
disproportionately low amounts. Given that a seed is nutritionally deficient in an amino
acid, which of the following amino acids would you automatically exclude as the one
limiting nutrient quality?
A. Methionine
B. Isoleucine
C. Glutamine
D. Lysine
CHEM-643 Amino Acid Metabolism Quiz
Friday, 20 November 2009
The figure to the right depicts the urea cycle in
mammals. During the catabolism of proteins for
energy, nitrogen from amino acids is channeled
into the urea cycle to form urea, a non-toxic
compound that is excreted.
Page 2
COO
COO
C O
H3N
C
CH2
Glu
CH2
PLP
COO
COO
KG
COO
COO
C
C O
H
R
2ADP + Pi
O
R
O
H2N
COO
H2N C NH2
14
____ 17. In a mouse, C from dietary sucrose,
shows up three days later in arginine
found in proteins. Which of the
following metabolic precursors of
arginine would contain the least amount
of 14C from dietary sucrose?
HCO3 + 2ATP
NH4
CH2
CH2
H3N
NAD(P)H+H+ NAD(P)
H
H3N
C
Orn
CH2
CH2
H2O
Pi
CH2
COO
H3N
C
Arg
CH2
NH3
COO
H
UREA CYCLE
CH2
NH
HN
C
NH
H3N
C
CH2
H
CH2
NH
H
H2O CH2
B. Citrulline
H2N
C
O
CH2
ATP
NH
OOC
CH
HC
D. Bicarbonate
C
Cit
COO
CH2
C. Pyruvate
H3N
CH2
CH2
A. Ornithine
C OPO3H
H
COO
HN
COO
COO
C
N
H
H3N
H
CH2
AMP + PPi
C
COO
H
Asp CH2
COO
COO
C O
R
PLP
COO
COO
C O
CH2
COO
H3N
C
H
R
____ 18. Based on the data in Table 3, which of the following transamination reactions would be
unlikely to be involved directly or indirectly in transferring amino groups into the urea
cycle?
A.
B.
C.
D.
Alanine + Oxaloacetate ↔ Aspartate + pyruvate
Valine + Pyruvate ↔ Alanine + α-Ketoisovalerate
Phenylalanine + Pyruvate ↔ Alanine + Phenylpyruvate
Histidine + α-Ketoglutarate ↔ Glutamate + Imidazolylpyruvate
____ 19. Which of the following compounds would be plentiful in a vegan diet.
A. Cholesterol
B. Polyunsaturated fatty acids
C. Vitamin B12
D. Creatine
____ 20. Leucine is missing from the data in Table 1 because the authors lost the sample.
However, given what is known now about leucine metabolism, what would be a
reasonable prediction and rationale for the missing data?
A. Because leucine is a lipogenic amino acid, it can’t be converted into sugars like
sucrose and therefore would be unlabeled.
B. Because leucine is derived from pyruvate that comes from the breakdown of sugars,
it should be labeled similarly to alanine, which also comes from pyruvate.
C. Because rats can’t biosynthesize leucine, no carbon from sucrose would show up in
leucine.
D. Leucine, being the most common amino acid in proteins, would dilute out any
labeled carbon in newly synthesized leucine derived from sucrose.
CHEM-643 Amino Acid Metabolism Quiz
Friday, 20 November 2009
Page 3
The diagram below illustrates the metabolic pathways that involve cysteine and methionine in
mammals. The two questions that follow relate to how well this diagram supports the data in
Tables 1-3 of the case study problem.
Protein
Synthesis
COO -
COO+
+
H3N
C
3PGA
H3N
H
+
H
PLP
H3N
OH
C
H 2O
SH
H2O
Cysteine
H2C
COO-
COO-
H3N
C
H
H
Adenosine
H
O
NH3+
COO-
CH2
H2O
CH2
NH2
-Ketobutyrate
SH
N
N5CH3FH4
O
H
H
OH
OH
B12
COO-
+
N
H3N
C
H
COO -
FH4
+
H
H3N
H
C
CH2
NH2
CH2
N
X-CH3
S
N
CH2
ATP
X
S+
H3C
S-Adenosyl
Methionine
Protein
Synthesis
H
CH2
S-Adenosyl
Homocysteine
TCA
Cycle
Homocysteine
N
S
N
CH3
Cystathionine
CH2
CH2
H2C
C
CH2
COO -
+
C
Dietary
Protein
NH4+
H2C
C
H3N
Protein
Synthesis
CH2
S
Serine
+
H
PLP
H2C
CH2
Dietary
Protein
C
COO-
CH2
N
O
N
Pi + PPi
H
H
OH
OH
H
Dietary
Protein
CH3
Methionine
H
____ 21. Pick the incorrect statement. The above diagram is consistent with:
A. Methionine being required for L-cell growth.
B. Cysteine being required for L-cell growth.
C. Methionine becoming labeled from 14C-surcose.
D. Cysteine becoming labeled from 14C-surcose.
____ 22. Table 3 does not include cysteine or methionine. If these sulfur-containing amino acids
had been used, what could you predict about the distribution of 15N between them two
after eight hours based on the diagram above?
A. 15N from methionine would significantly label cysteine, but not the reverse.
B. 15N from cysteine would significantly label methionine, but not the reverse.
C. 15N from methionine or cysteine would not be transferred to the other.
D. 15N from cysteine would significantly label methionine and vice versa.
____ 23. Methionine is classified an essential amino acid for mammals, which means mammals
must get the amino acid in their diet to survive, yet it contains radioactivity derived
from 14C sucrose. The best explanation for this observation is:
A. Experimental Error.
B. Mammals can make methionine, but not enough to survive.
C. Only the methyl group is labeled and comes from serine and glycine.
D. The label is derived from cysteine.
CHEM-643 Amino Acid Metabolism Quiz
Friday, 20 November 2009
Page 4
____ 24. The Lehninger textbook notes that in mammals the biosynthetic routes to proline and
ornithine/arginine from glutamate may not be separate as described in lecture. Rather
the synthesis of proline would branch off of the pathway to arginine from the
intermediate ornithine as shown below with the long diagonal line.
+
TCA Cycle
KG
COOH3N C H
CH2
NADPH
CH2
C
O O PO3H-
COOH2O
COOH
N
H3N C H
Spontaneous
CH2
NADPH
NADP
CH2
Glu
C
O H
COOH
+
HN
NADP
Proline
PLP
ADP
KG
ATP
AcCoA
CoASH
COOH2N C H
CH2
Glutamate
CH2
COO-
COOH3N C H
CH2
Ornithine CH
2
CH2
NH3+
+
Urea Cycle
& Arginine
O
COOO
COOO
COOO
COOH
H
H
H
H3C C N C H H3C C N C H
H3C C N C H PLP H3C C N C H
CH2
CH2
CH2
CH2
Glu
KG
NADP
NADPH
CH2
CH2 ATP ADP
CH2
CH2
+Pi
CH2
COOC
C
O O PO3H
O H
NH3+
The following true statements based on Tables 1 and 3 may or may not support the
hypothesis that ornithine is an intermediate in proline synthesis.
I. The 14C content of proline is essentially same as that of arginine.
II. The 14C content of proline is much less than that of glutamate.
III. 15N from arginine is readily transferred to proline.
Which of the above statements support the branched pathway compared to the direct
pathway to praline from glutamate?
A. I and II
B. I and III
C. II and III
D. I, II, and III
CHEM-643 Amino Acid Metabolism Quiz
Friday, 20 November 2009
Page 5
Table 1. Specific radioactivity of amino acids biosynthesized from 14C sucrose in three days by a mouse (Steele,
1952).
Amino Acid nCi/mgC
Amino Acid nCi/mgC
Glutamate
19.0±1.9
Threonine
nCi/mgC
Amino Acid nCi/mgC
0.02±0.01
Lysine
0.0±0.02
Aspartate
15.8±0.9
Serine
8.4±0.1
Phenylalanine 0.02±0.07
Histidine
0.07±0.08
Alanine
26.5±3.3
Glycine
5.1±0.2
Tyrosine
0.0±0.07
Cystine
3.3±0.3
Proline
3.1±0.1
Isoleucine
0.06±0.05
Arginine
3.0±0.2
Methionine
0.09±0.02
Amino Acid
Valine
1.03±0.06
Table 2. Growth of mouse L cells in media lacking the indicated amino acid (Eagle, 1955).
Amino
Acid
Cell
Growth
Amino
Acid
Glutamate
3.6 - 4.5
Threonine
Aspartate
3.6 - 6.1
Serine
Alanine
2.2 - 2.6
Proline
2.4 - 6.8
Cell
Growth
Amino Acid
0.2
Cell
Growth
Amino
Acid
Cell
Growth
Valine
0.06 - 0.2
Lysine
0.2 - 0.5
2.5 - 2.8
Phenylalanine
0.3 - 0.4
Histidine
0.3 - 0.4
Glycine
3.6 - 3.7
Tyrosine
0.06 - 0.2
Cystine
0.1 - 0.3
Isoleucine
0.1 - 0.4
Arginine
0.4 - 0.9
Methionine
0.3 - 0.4
Leucine
0.4 - 0.6
Tryptophan
0.3 - 0.4
Table 3. Distribution of 15N among the amino acids of liver proteins 8 hours after intravenous injection of
various amino acid sources of 15N. Values are normalized to the 15N content of the source amino acid (100)
incorporated into protein (Aqvist, 1951).
Amino acids incorporated into rat liver proteins
15
Glu Asp Ala Pro Thr Ser Gly Leu Ile Val Phe Tyr Arg Lys His
Glutamate
100
74
12
3
46
19
31
nd
20
14
20
34
4
2
Aspartate
186 100 125
29
2
40
38
49 111
nd
26
38
60
15
25
16 <1
23
21
38
40
29
9
10
33
4
3
1
5
3
4
5
5
1
2
11
2 <1
2 100
20
14
1
2
4
2
5
5
1 <1
14 100
50
3
2
2
2
6
9
1
1
88 100
nd
nd
nd
3
nd
16 <1
2
25
12
3
7
11
0 <1
34 100
15
8
12
10
4
3
41 100
5
6
14
1
2
74
10
7
2
44 100
9
1
1
10 100
13
5
9 100
4
N-Amino Acid
50
Alanine
77
44 100
Proline
23
14
Threonine(1)
6
5
5
Serine
9
9
12
2
Glycine
19
12
16
1
Leucine
30
15
25
nd <1
7
7 100
Isoleucine
28
14
23
11 <1
9
8
Valine
34
19
29
7
0
12
10
46
Phenylalanine
24
12
18
2 <1
3
2
3
5
3 100
Tyrosine(2)
23
13
16
3 <1
4
4
4
5
4
(3)
34
23
20
18
2
6
1
nd
nd
nd
11
23
19
12
5
3
8
3
nd
nd
nd
6
nd
28
25
30
6
2
8
10
nd
nd
nd
9
nd
Arginine
Lysine3
Histidine
3
18 100
0
1. Slightly contaminated with 15N serine. Data from one rat only.
2. Administered by a stomach tube. Animals killed after 12 hours.
3. 15N excess significantly less than for other administered amino acids.
24
6 100
CHEM-643 Amino Acid Metabolism Quiz
Friday, 20 November 2009
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Page 6
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