The Biological Pathway

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Figure 4: Oxidative pathways of ethanol

Ethanol is mainly oxidized to acetaldehyde through three different enzymes: alcohol dehydrogenase, cytochrome P450 2E1, and catalase. To avoid acetaldehyde’s toxic effects, after it is produced, acetaldehyde must be oxidized to acetate by aldehyde dehydrogenase. Acetate can be catalyzed to acetyl-CoA by acetyl-CoA synthetase, and the acetyl-CoA formed can feed into the citric acid cycle or be used in lipid biosynthesis (5).


  1. Honestly I think this is exactly the figure that was missing from “the Answer” page! I think your caption could be slightly more descriptive. I know when I look at a figure, especially if it’s before the paragraphs of text, I don’t want to have to look through the paragraphs in order to know what “ALDH” stand for, for example. (Or you could write out “aldehyde dehyrdrogenase” on the figure, it’s not that long).

    Also, why is the conversion of acetate to acetyl-CoA shown as multiple steps when you describe it as only one enzyme?

  2. Like Delia, I am also interested as to why the conversion of acetate to acetyl Co-A is multiple steps.

    My only other revision is that you mention the acetyl Co-A created can be used in the CAC or for lipid biosynthesis, but only mention the CAC in the diagram. Would it be possible to add a second arrow indicating the alternative lipid biosynthesis outcome?

  3. Do you remember the graphs Dr. Pamuk has made in class for glucose metabolism that show the primary processes happening at certain time points? (i.e. in the first several hours post eating glycolysis provides energy, then glycogen breakdown can provide energy for 24-48 hours, then gluconeogenesis, muscle breakdown, and lipid breakdown begin to occur). I think it would help summarize alcohol metabolism to do a similar graph showing ADH, CYP450 and catalase activity as a function of alcohol ingested, since these enzymes catalyze the same reaction. Your next three pages do a really great job of explaining how these enzymes adapt as alcohol consumption rises, and it could be a good visual highlight.

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