- The following questions will help you review concepts presented in this module.
Consider the following reaction:Monoamine oxidase
Dopamine + Oxygen —————-> DPA + H2O2 + NH3
H2O
In this example, which of the following is oxidized and which is reduced?
- Dopamine is oxidized, hydrogen peroxide is reduced
You are half-correct! Dopamine is oxidized by O2; it donates an electron (associated with the H) from its CH3 group to molecular oxygen (O2). Hydrogen peroxide is formed by the reaction in the presence of H2O. - 2. Dopamine is reduced, oxygen is oxidized
Sorry, try again. Dopamine is oxidized by O2; it donates an electron (associated with the H) from its CH3 group to molecular oxygen (O2). The O2 is reduced because it accepts the electron from dopamine. - Dopamine is oxidized, oxygen is reduced
Hooray! Dopamine donates an electron (associated with the H) from its CH3 group to molecular oxygen (O2). The O2 then becomes reduced. - Dopamine is reduced, hydrogen peroxide is oxidized
Sorry, try again. Dopamine is oxidized by O2; it donates an electron (associated with the H) from its CH3 group to molecular oxygen (O2). Hydrogen peroxide is formed by the reaction in the presence of H2O.
- Dopamine is oxidized, hydrogen peroxide is reduced
- In this module, you learned that the neurotransmitter dopamine is oxidized by molecular oxygen (O2) with the help of an enzyme called monoamine oxidase. This means that the oxygen:
- Donates a proton to dopamine
Try again. When a compound is oxidized, it loses electrons and the species that causes the oxidation gains the electrons. With the aid of the enzyme, the O2 tends to accept a single electron from dopamine. - Accepts a proton from dopamine
Try again. When a compound is oxidized, it loses electrons and the species that causes the oxidation gains the electrons. With the aid of the enzyme, the O2 tends to accept a single electron from dopamine. - Donates an electron to dopamine
Try again. When a compound is oxidized, it loses electrons and the species that causes the oxidation gains the electrons. With the aid of the enzyme, the O2 tends to accept a single electron from dopamine. - Accepts an electron from dopamine
Bravo! When a compound is oxidized, it loses electrons and the species that causes the oxidation gains the electrons. With the aid of the enzyme, the O2 tends to accept a single electron from dopamine.
- Donates a proton to dopamine
- Methamphetamine, a central nervous system stimulant, causes increased alertness and agitation by causing:
- Oxidation of dopamine
Sorry, that is incorrect. Although methamphetamine causes oxidation of dopamine, it is unrelated to its actions as a stimulant. - Rapid onset Parkinson’s disease
Sorry, that is incorrect. Methamphetamine’s ability to cause oxidation of dopamine may damage neurons, similar to the effects of Parkinson’s disease. - Release of dopamine
Good answer! Methamphetamine, like amphetamine, causes the release of the neurotransmitter dopamine into the synaptic space. This is the basis for its stimulant activity. - Formation of free radicals
No, try again. Methamphetamine causes oxidation of the neurotransmitter dopamine, which can lead to the generation of oxygen radicals. This action is unrelated to its actions as a stimulant, but it can damage neurons.
- Oxidation of dopamine
- When a drug user takes methamphetamine, it releases the neurotransmitter dopamine into the synaptic space. There, the dopamine is autooxidized by O2, without the help of enzymes. In this case the autooxidation of dopamine results in the production of an unstable molecule called:
- Hydrogen peroxide (H2O2)
Not quite. Hydrogen peroxide is produced when dopamine is oxidized with the help of the enzyme, monoamine oxidase. It is not formed by the autooxidation of dopamine. - Superoxide radical (O2*-)
You’re right! When dopamine is autooxidized, O2 gains an electron, providing it with an extra unpaired electron. This compound is a free radical known as superoxide and it has 13 electrons in its outer orbital making it very unstable. - Ammonia (NH3)
Not quite. Ammonia is produced when dopamine is oxidized with the help of the enzyme, monoamine oxidase. It is not formed by the autooxidation of dopamine. - Oxygen
Wrong answer. Oxygen is required to oxidize dopamine – it is not generated by the oxidation of dopamine.
- Hydrogen peroxide (H2O2)
- In this module you learned about some of the dangers of free radicals in the body. Free radicals oxidize lipids, proteins, and DNA, disorganizating their structure. Which of the following is a consequence of the oxidation of lipids in a cell membrane?
- Water leaves the cells and causes them to shrink
Try again. Oxidation of membrane lipids by free radicals makes them kinky. This destroys the membrane structure and the membranes become leaky. Water enters the cell, causing it to swell and eventually burst. - The carbon chains in the lipids can get kinky causing the cell to become leaky
Bravo! Oxidation of membrane lipids involves the loss of hydrogen atoms (and electrons) from the carbon chains. This alters their structure and the chains become shortened and kinky. The lipids no longer form a tight membrane barrier, so the cell becomes leaky. - Disulfide bonds are formed
Incorrect. Disulfide bonds are generated by the oxidation of proteins that contain sulfur-hydrogen molecules. The SH molecule loses a hydrogen atom (and electrons) to produce the double bond between two S atoms. This destroys the action of the protein so that the cell doesn’t function properly.
- Water leaves the cells and causes them to shrink
- As you have learned, oxygen radicals can produce a range of detrimental effects. One way in which our bodies reduce the damage caused by oxygen radicals is to:
- Increase release of dopamine
Sorry, that’s not right. The presence of excess dopamine actually results in autooxidation of this compound, which produces more oxygen radicals. - Increase exposure to UV radiation
Sorry, that’s not right. UV radiation causes oxidative damage to cells and increases formation of oxygen radicals. - Activate enzymes that scavenge oxygen radicals
You’re right! To keep the level of oxygen radicals low in our bodies, oxygen radicals are “scavenged” by enzymes to render them harmless. For example, superoxide radicals are reduced with the help of the enzyme superoxide dismutase to form hydrogen peroxide (H2O2), which is then detoxified by the enzyme catalase which converts it to water and O2.
- Increase release of dopamine
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