Question

Methanol and ethanol are oxidized by alcohol dehydrogenase. In methanol poisoning, ethanol is given intravenously to prevent the formation of formaldehyde that has toxic effects. a. Draw the condensed structural formulas of methanol and ethanol. b. Would ethanol compete for the active site or bind to a different site? c. Would ethanol be a competitive or noncompetitive inhibitor of methanol oxidation?

Short answer

a. Methanol: CH₃OH, Ethanol: C₂H₅OH b. Ethanol competes for the active site. c. Ethanol is a competitive inhibitor.

Step-by-step solution

- Draw Condensed Structural Formulas

The condensed structural formula for methanol is CH₃OH. The condensed structural formula for ethanol is C₂H₅OH.

- Determine Ethanol's Interaction with the Active Site

Ethanol would compete for the active site with methanol because both are substrates for the same enzyme, alcohol dehydrogenase.

- Classify Ethanol as an Inhibitor

Since ethanol competes for the same active site as methanol, ethanol acts as a competitive inhibitor for methanol oxidation.

Key concepts

Methanol Poisoning

Methanol, also known as wood alcohol, is toxic when ingested. When methanol is processed by our bodies, it is converted into formaldehyde and then to formic acid. These substances are very harmful. They can lead to metabolic acidosis, blindness, and even death.
Symptoms of methanol poisoning include headache, dizziness, nausea, and blurred vision.
It may also take from 12 to 24 hours for symptoms to appear. If a person is suspected of methanol poisoning, they must receive immediate medical attention.

Ethanol

Ethanol is the type of alcohol found in alcoholic beverages. It is less toxic compared to methanol.
However, when used medically, it can act as an antidote to methanol poisoning. This is because ethanol competes with methanol for metabolism by the same enzyme, alcohol dehydrogenase.
By administering ethanol, the metabolism of methanol is slowed down, which allows more time for methanol to be excreted from the body.

Competitive Inhibition

In competitive inhibition, two substances compete for the same active site on an enzyme.
In the context of methanol poisoning, ethanol competes with methanol for the active site on the enzyme alcohol dehydrogenase. This competition prevents methanol from being converted into toxic formaldehyde.
As a result, ethanol can be used to mitigate the toxic effects of methanol ingestion.

Active Site

The active site of an enzyme is the region where substrate molecules bind and undergo chemical reactions.
Alcohol dehydrogenase, the enzyme in question, has an active site that binds to both methanol and ethanol.
When ethanol is present, it blocks methanol from binding to the active site, thereby preventing the enzyme from converting methanol into toxic products.

Oxidation

Oxidation refers to the chemical process of losing electrons.
In the case of alcohol dehydrogenase, this enzyme catalyzes the oxidation of methanol to formaldehyde and ethanol to acetaldehyde.
These reactions involve the loss of electrons from the alcohols, turning them into aldehydes.
The oxidation of methanol is particularly harmful because formaldehyde is toxic, whereas the byproducts of ethanol oxidation are less harmful in the short term.