Case Study Section 3 – Ox. Phos. Based on “Wrestling with Weight Loss: The Dange
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Question
Case Study Section 3 – Ox. Phos.
Based on “Wrestling with Weight Loss: The Dangers of a Weight-Loss Drug” by Susan M. DeSimone and Annie Prud’homme-Genereux and “A Diet to Die For: An Exploration of Oxidative Phosphorylation” by Terry Platt and Eric Ribbens (National Center for Case Study Teaching in Science)
The Situation:
A good friend of yours, Connor Sick, is a member of the WVU wrestling team but has been struggling to make the weight class his coaches and he know he would be most competitive at. He has heard of a diet drug that is claimed to REALLY work. Connor knows you are taking Introduction to Biochemistry so he comes to you and asks you for advice on whether he should try the drug.
The information Connor found online said that DNP had helped several people lose weight but that you needed to be careful with dosage. Some of the side effects included a fever, cataracts, and rashes. There were even some reports of deaths. DNP was said to be a mitochondrial uncoupler.
You tell Connor that you will look into it and get back to him. Your initial research determines that DNP is 2,4-dinitrophenol and has the following structure:
Question 1:
Based on the structure of DNP does it appear to be:
A. Mostly hydrophilic
B. Mostly hydrophobic
C. It is impossible to tell
You also learn that DNP can donate protons and has a pKa of 4.114, thus is classified as a weak acid.
Question 2:
You know from your biochemistry course that a proton gradient forms in the mitochondria, which statement best describes this?
A. There is a greater [H+] in the intermembrane space, between the outer and inner mitochondrial
membranes.
B. There is a greater [H+] in the mitochondrial matrix, inside the inner membrane.
C. There is a greater [H+] in the cytosol surrounding the mitochondria, outside the outer membrane.
D. Under normal conditions there isn’t a gradient, the [H+] is equal in all parts of the mitochondria.
Question 3:
Based on this information and the fact that DNP is labeled as a mitochondrial uncoupler, which of the following statements would best describe DNP’s mechanism of action?
A. DNP dissolves in the outer mitochondrial membrane and allows protons to flow into the cytosol,
thus negating the gradient.
B. DNP dissolves in the intermembrane space and binds protons, thus negating the gradient.
C. DNP dissolves in the inner mitochondrial membrane and allows protons to flow into the matrix,
thus negating the gradient.
D. DNP flows freely between all compartments of the mitochondria and carries protons with it, thus
negating the gradient.
Question 4:
By negating the proton gradient in the mitochondria, what does DNP uncouple?
A. Electron transport from ATP synthesis
B. Reduction of oxygen to water from ATP synthesis
C. Generation of NADH and FADH2 during metabolism from ATP synthesis
D. All of the above
E. Nothing, the description is misleading
In the searches you have done you find a research article describing an experiment where muscle cells grown in culture were exposed to DNP and the rate of ATP production and glucose oxidation were measured and the following data were obtained:
At this point Connor comes back to you and asks “Will it work? Will I lose weight if I take DNP?”
Question 5:
Which of the following is the most accurate answer given the information you have gathered?
A. Yes, you could lose weight because it would require your body to burn more fuel (ie. glucose,
fats, etc…) to produce the ATP your body needs.
B. Yes, you could lose weight because your body would produce less ATP so you wouldn’t adsorb as
many nutrients from your food.
C. No, you probably wouldn’t lose weight because your body would produce less ATP so you
wouldn’t be able to exercise as much.
D. No, you probably wouldn’t lose much weight because it only affects the mitochondria and they are really tiny and don’t contribute to your overall weight much.
You also show Connor a clinical report you found about another wrestler, Charles, that used DNP to lose weight quickly who ended up taking a double dose because he was afraid he wouldn’t make his weigh-in. Charles was admitted to the hospital with symptoms including: being flushed, breathing fast, excessive sweating, nausea, and weakness in his knees. Charles had experienced an overdose of DNP, which caused all of his symptoms.
Question 6:
Charles’s flushed face and sweating were caused by a high fever. What is the most likely explanation for the fever?
A. The lack of a mitochondrial proton gradient caused the mitochondria to become sick and die,
thus causing the fever.
B. The protons used to make the gradient have energy associated with them that normally drives
ATP synthesis but when the gradient is negated by DNP the energy is released as heat.
C. DNP was recognized as non-self by Charles’s immune system and a fever was part of the defense
mechanism.
D. The fever had nothing to do with his taking DNP, he was just sick.
Question 7:
What is the best explanation for Charles’s rapid breathing during the DNP overdose?
A. He was hyper ventilating in response to less oxygen entering his body.
B. The heavy breathing was all in response to his fever, like panting in a dog.
C. His electron transport chain had increased activity to off-set the protons transported by DNP so more oxygen was required to accept the electrons, the rapid breathing was his body’s way to try
to get more oxygen.
D. He was excited about his weight loss and upcoming match.
Question 8:
What is the best explanation for Charles’s weakness and nausea?
A. The lack of ATP being produced by Charles’s muscles in response to the DNP made muscle
contraction more difficult, thus the weakness.
B. Increased rates of metabolism to off-set the actions of the DNP caused a drop in blood glucose
causing both weakness and nausea.
C. Both A and B are likely explanations.
D. Charles was just excited about his weight loss and nervous about his upcoming match.
You explain all these risks to Connor but he isn’t convinced. He remembers hearing about a protein called Uncoupling Protein in his freshman biology class that functions similarly to DNP. He argues that if a naturally occurring protein does the same thing how can DNP be dangerous?
Question 9:
Which of the following would be the most appropriate explanation?
A. Uncoupling proteins are not expressed in humans.
B. Uncoupling proteins have a very different mode of action than DNP.
C. Uncoupling proteins only exist in a tissue called brown adipose tissue that only exists in infants.
D. Uncoupling proteins are highly regulated and only active when needed and not to the excess of
causing problems while DNP has no regulation beyond how much you take.
Question 10:
Which of the following would be situations when uncoupling proteins would be active (select all that apply)?
A. A hibernating bear
B. A dog in the summer trying to rid itself of excess heat
C. A mouse at room temperature (note that thermoneutral for a mouse is ~30°C)
D. A premature infant with very little fat stores
E. An adult human at maintenance (ie.at a healthy body weight and not gaining or losing weight)
F. An adult human post-Thanksgiving dinner (ie. much greater Caloric intake than normal)
OH NO2 NO2 NO2 NO2 2,4-Dinitrophenol (DNP) NH F-C-F F-C-F Carbonylcyanide-p- trifluoromethoxyphenylhydrazone (FCCP) Figure 19-21 Lehninger Principles of Biochemistry, Fifth Edition O 2008 W.H. Freeman and CompanyExplanation / Answer
1 . B
2 . A
3 . C
4 . D but more specifically A
5 . B
6 . B
7 . C
8 . C
9 . D
10 . A , C , D , F