Studying metabolism with galvanic cells
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Studying metabolism with galvanic cells
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[post_date] => 2025-01-09 08:13:36
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[post_content] => Practice Passage (Question 1-4)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Researchers recently reported the design of a glucose/O2 galvanic cell. A description of the cell is provided below. It may be helpful to draw out the cell.
Essentially, the researchers used enzymes naturally found in the body to facilitate the oxidation and reduction reactions involving glucose and oxygen, respectively, in the two separate half cells of the galvanic cell. Because only one enzyme was used in the oxidation of glucose, the oxidation of glucose was not complete (i.e. no carbon dioxide was produced).
A carbon-based metal served as an anode and cathode in both cells; each electrode was attached by a wire that stretched between the two half cells to serve as a passage for electrons. The shape and small size of the pores in the electrodes allow electron transfer to occur more efficiently with biological enzymes whose functional groups were buried deep inside the protein. The flow of electrons, or current, created by this galvanic cell was enough to power a Light-Emitting Diode inserted into the wire circuit between the two half cells, demonstrating its electrical-powering abilities.
Reuillard, B. et al. High power enzymatic biofuel cell based on naphthoquinone-mediated oxidation of glucose by glucose oxidase in a carbon nanotube 3D matrix. Phys. Chem. Chem. Phys. 15, 4892–4896 (2013).
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[question] => Which of the following designations for the oxidation and reduction half cells is correct?
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[answer] => 2
[description] => Reason for the Correct Answer:
Oxidation occurs at the electrode in an electrochemical cell called an “anode” and reduction occurs at the electrode called a “cathode”.
Glucose is oxidized and oxygen is reduced.
Since glucose is oxidized, this reaction must be taking place at the anode. Since oxygen is being reduced, this reaction must be taking place at the cathode.
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[answers] => Array
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[0] => Array
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[each_answer] => A. O2 is oxidized at the anode, glucose is reduced at the cathode
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[each_answer] => B. Glucose is oxidized at the anode, O2 is reduced at the cathode
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[each_answer] => C. Glucose is oxidized at the cathode, O2 is reduced at the anode
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[each_answer] => D. O2 is oxidized at the cathode, glucose is reduced at the anode
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Researchers had many different carbon fuels available at their disposal in addition to glucose. These included: a 10-carbon saturated fatty acid, a 5-carbon unsaturated fatty acid, and a 50-amino acid long protein. If researchers were able to isolate enzymes to facilitate the complete oxidation of each of these fuels into their most oxidized products, which fuel would produce the most current?
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[answer] => 3
[description] => Reason for the Correct Answer:
Current describes the flow of electrons; more current = more electrons.
The complete oxidation of a fuel yields electrons. Which fuel is the most reduced? In other words, what fuel can undergo the most oxidation?
A saturated fatty acid is the most reduced of the molecules listed above (think about all the electrons stored in the C-H bonds in the fatty acid tail).
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[each_answer] => A. 50-amino acid-long protein
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[each_answer] => B. 5-carbon unsaturated fatty acid
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[each_answer] => C. 10-carbon saturated fatty acid
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[each_answer] => D. Glucose
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[question] => All of the following molecules are involved in harnessing the flow of electrons from glucose to oxygen in the body EXCEPT:
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[answer] => 1
[description] => Reason for the Correct Answer:
NAD+ is reduced to NADH during the catabolic breakdown of a fuel (e.g. glucose).
The electron transport chain accepts electrons from electron carrier molecules to fuel the production of ATP.
Dehydrogenase enzymes facilitate the oxidation of substrates that reduce electron carrier molecules; NADP+/NADPH are primarily involved in anabolism.
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[0] => Array
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[each_answer] => A. NADP+
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[each_answer] => B. NAD+
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[each_answer] => C. Electron Transport Chain Proteins
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[each_answer] => D. Dehydrogenase enzymes
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[quiz_unique_key] => 2261298308
[question] => What would you expect to observe with regard to the current if more than one enzyme facilitated the complete breakdown of glucose instead of a one-enzyme partial breakdown of glucose?
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[answer] => 1
[description] => Reason for the Correct Answer:
Current describes the flow of electrons; more current = more electrons.
The complete breakdown of glucose in multiple steps will allow more electrons to be oxidized from the glucose.
Since a complete breakdown of glucose will produce more electrons, current will increase.
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[0] => Array
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[each_answer] => A. The current will increase
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[each_answer] => B. Its kinetic energy will increase as it passes through the field.
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[each_answer] => C. The current will decrease
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[each_answer] => D. There is not enough information
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[question] => What is a function of the wire in the system
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[answer] => 3
[description] => Reason for the Correct Answer:
In addition to serving as an outlet for electrons to charge the light diode, the wire also serves as a salt bridge.
The wire does not drive the electrons to go anywhere, it simply acts as a path through which the electrons can travel. In the same vein, the wire does not produce any current itself.
The purpose of a salt bridge is to balance the growing positive charge in the anode and negative charge in the cathode. Without the salt migration, the charge imbalance would become too great and the reaction would stop.
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[each_answer] => A. To generate electrons to produce a current
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[each_answer] => B. To induce the current to go in a nonspontaneous direction
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[each_answer] => C. To replenish charges to allow the reaction to occur longer
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[each_answer] => D. To drive the electrons to move from the anode to the cathode
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[559163|1] => B
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[559163|3] => A
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