Study guide for Midterm 2 BIS103-002 FQ2012 (part 2 of 2)
November 11th, 2012
40. One of the reactions to make succinyl-CoA requires exchange of an –CO-SCoA group with a
hydrogen atom. This reaction depends on a specific prosthetic group. Name the enzyme that
catalyzes this reaction. Which prosthetic group does this reaction depend on?
41. Compare glycogen, glucose and fat as energy source. The question in next pages is from a
previous year's exam.
NOTE-1: it is possible that the question something like this may be included in our MT2, but the
reading portion should be shorter.
NOTE-2: Answer key to this question will be provided by noon on Tuesday November 13th .
---------------------------------------------------------------------------------------------------------------We will discuss #42-47 at the class on Tuesday November 13th.
42. We should be able to name and draw structures of the three ketone bodies.
43. The liver is generous. For example, as we saw at MT1 Q2(g), the liver shares energy stored in
glycogen with other cells (we should review that question). The liver is generous regarding
ketone bodies, too: actually the liver acts as a provider of ketone bodies and not as a consumer.
The liver makes ketone bodies but does not use them as an energy source. Give the reason for this
by defining how ketone bodies are produced and used (enzymes, reactants/products, location).
44. Name the theory regarding phosphorylation of ADP originally proposed by Peter Mitchell. What
was the opposing idea when it was proposed? How was the Mitchell’s hypothesis proven?
45. Electrons released from glycolysis, PDC, TCA cycle, and fatty acid β-oxidation are fed into ETC.
Explain how. (keypoint: location)
46. Why are “transports” of oxaloacetate, malate, NADH, NAD+, ATP, ADP, Pi, CoA, and acyl-CoA
from the cytoplasm to mitochondria matrix, or vice versa, important?
47. How are the transports of the metabolites listed in #46 across the mitochondria inner membrane
achieved ? Hint: are there transporters for them in the inner membrane? If so, the answer is” by
a transporter”. If not, they would use a shuttle service (e.g., hat exchange). What kind of shuttle?
There will be no post-class 14 assignment.
3. Metabolic sources of energy for hummingbird flight.
Hummingbirds in sustained hovering flight (short-term flight) have the highest weight specific
metabolic rates EVER recorded among the vertebrates as of 1986. The flight muscles that
make this possible are exceptionally large, making up 21-35% of total body weight. In order to
gain insights into the metabolic sources of energy for hummingbird’s hovering flight, a group
of researchers in Canada conducted the following experiments.
First, they caught several hummingbirds in southern British Columbia before the migration
season. Then they kept birds in the cages containing feeders which required the birds to hover
a short distance to feed. The regular diet consisted of nectar concentrates. The birds were also
supplied with fruit flies to supplement the diet and to provide additional exercise. In the end,
however, the birds were decapitated and their flight muscle tissues were isolated. Proteins in
the tissues were extracted with appropriate buffer, and activities of various enzymes in the
protein extracts were measured in the optimized condition*. The data are summarized in the
following table.
Table. Maximum enzyme activities in hummingbird flight muscle.
Enzyme
#
Activity: mean (μmol product/min gram wet
weight of muscle) ± standard error
Number of birds
examined
1
Glycogen phosphorylase
31.22±2.5
6
2
Hexokinase
9.18±0.31
4
3
Phosphofructokinase I
109.8±13
6
4
Pyruvate kinase
672.4±27
6
5
Lactate dehydrogenase
230.3±23
6
6
Carnitine acyltransferases
4.42±0.46
6
(sum of I&II)
7
L-hydroxyacyl-CoA dehydrogenase
97.10±13
6
8
Citrate synthase
343.3±8.8
6
9
Malate dehydrogenase
3525±331
6
*As you may recall, an enzyme can catalyze reactions of both directions. In the case presented here, the
activity of nine enzymes in the protein extract was measured individually with a substrate and all of the
necessary co-substrates in the appropriate buffer under the optimized condition (in vitro), and quantified as
the amount of the product per minute, gram wet weight of muscle. Although this in vitro assay measured the activity of
one direction of a given enzyme, one can assume that if the activity is high, the enzyme should be highly
active in either that or opposite direction depending on the ratio of [products] to [reactants] in the living
muscle tissue (in vivo). Conversely, if the measured activity in one direction in vitro is low, one may assume
that the enzyme would not be very active in either direction in vivo.
(a) (2pts) Based on the results, the Canadian researchers concluded that the hummingbird flight
muscle is highly aerobic. Circle ONE, the most appropriate description, which supports their
conclusion. (four choices)
activity of enzyme #1 is very high
activity of enzyme #8 is very high
activity of enzyme #5 is very high
activity of enzyme #3 is very high
(b) (3pts) If it is assumed that glucose is the sole substrate for hovering flight, a stead-state rate
of glucose utilization of 16.8 μmol/min gram wet weight of muscle is required. If it is assumed that
oleic acid (an unsaturated fatty acid, the main fat component in the hummingbird muscle) is
the only substrate used, hovering flight would require a rate of its oxidation of 4.2 μmol/min
gram wet weight of muscle.
Based on the results, which one of the following three metabolic sources is the most
appropriate substrate that, when oxidized exclusively, could sustain the hummingbirds’
muscle work at its highest intensity?
Circle ONE (three choices)
fat
free sugar (glucose, fructose, sucrose, etc)
glycogen
(c) (9pts) Briefly explain why you did, or did not choose each of the three energy sources in (b).
Your answers must fit in the space below in this page. (3pts x 3)
<fat> You
Because….
chose or
<free sugar> You
Because….
<glycogen> You
Because….
chose
did not choose (circle one)
or
chose or
did not choose (circle one)
did not choose (circle one)