Question

While testing amylase activity, John uses a buffer of pH 6 and substrate starch. He incubates them at 104ºF (40ºC). All the tubes show glucose formation, except one, which had no starch solution. Why did this happen?

Answer 1

starch (polymer of glucose) is broken up into individual glucose molecules by amylase. You can't have the product (glucose) without the starting material (starch).

Answer 2

@aaronq The question does not indicate that amylase was used.

@december21st If there was no amylase, the heat can break some of the bonds and release glucose. Obviously since starch is made up of glucose, no starch = no glucose.

Answer 3

yes it does, it says "He incubates them" meaning the enzyme + substrate. 40 Celsius is not warm enough to break these bonds even at a the slightly acidic pH.

Why would the say "testing amylase activity" and not include the enzyme? lol

Answer 4

@aaronq Have you ever done this experiment? I have, and I run it every semester. The incubate simply means maintain a certain temp (from Latin meaning to hatch or similar). As for why the amylase is left out, when you do this experiment the amylase is denatured, permanently, at the higher temps, so to keep everything as similar as possible, you incubate the substrate and then add the amylase. This way we can remove the extra variable of heating with substraet and heating without substrate.

You are right that @ 40C there will be little breakage of amylose, but you are wrong to think it will not occur. You will have some glucose, very few, but some; especially when exposed to light. Given enough time, light will cause the complete "digestion" to glucose monomers.

Answer 5

yep, i've ran this experiment before, the staple \(\alpha\)-amylase, KI starch-detection. I've also done several other experiments involving other enzymes. Anytime the term "incubate" has come up, it has involved enzymes.

Because the question states "While testing amylase activity", and nowhere else in the question do they suggest that they aren't using the enzyme, i think that it's logical to assume they are - in fact - using the enzyme. And while you are right that sunlight can be used to break the acetal bonds and it would be ideal to find the baseline rate of hydrolysis, it would take a very long time, I don't see this being common in a lab - specially a student lab.

More importantly, they are testing the activity of amylase, why would they only use the denatured enzyme? Running the experiment how you are suggesting would be pointless.