# Biochemistry question - (Dec/23/2008 )

Questions are excerpted from Deborah Goldberg AP Biology:

"Questions 5-11
In a lab experiment, one enzyme is combined with its substrate at time 0. The product is measured in micrograms at 20-second intervals and recorded on the data table below.

Time(s) 0 (space) 20 (space) 40 (space) 60 (space) 80 (space)100 (space) 120
Product 0.0 (space)0.25 (space) 0.50 (space) 0.70 (space) 0.80 (space)0.85 (space) 0.85
(micrograms)

7. Why is there no increase in product after 100 seconds?

8. What would happen if you added only more enzyme after 100 seconds?

9. What would happen if you added only more substrate after 100 seconds?"

I know that this might seem like a homework question, when in fact this is NOT a homework question - I am trying to study for a big test soon by practicing on practice questions.

I will leave a bunch of space here so that your answers will not be influenced by the actual answers that I will type out below.

"7. There is no increase in product after 100 seconds because all the enzymes are saturated and are already catalyzing reactions as fast as they can.

8. Assuming there is excess substrate that enzyme is not colliding with, an addition of enzyme after 100 seconds would increase the rate of reaction until the enzyme, once again, became saturated.

9. If you add more substrate after 100 seconds, there would be no change because the enzyme is saturated and reacting with as much substrate as it can. The enzyme cannot handle any more substrate. If you added both substrate and enzyme after 100 seconds, the reaction rate would increase temporarily until the enzyme became saturated once again."

The work I did for this problem (as I did spend much time on this set of questions) is shown below.
I reasoned as follows: - Well the product is what was made, right? So if you look at times 100 and 120, you can clearly see that there was no increase in product (as question 7 pointed out). But that would mean that from 100 to 120, nothing was made, right (because once again the product is what you end up with, or, in other words, what you make)?????????? So it follows that (and this was my answer to question 7) there was no increase in product because, well, the reaction had finished, right????? So if you added more enzymes (question eight), no reaction would occur and you would still have the same amount of product (which was the substrate). It would also follow, then (question 9), that if you added only more substrate after 100 seconds, then the reaction would resume (as the one enzyme you had in the beginning would work again) and there would be more and more product until that reaction, too, was finished and then the product would remain the same.

Now, having explained my reasoning, can someone please explain to me why my reasoning was faulty???????????????? I'm not sure about this, but I have a hunch - I think that my reasoning fell apart, as after this step, my reasoning from there looks pretty good - I think that I assumed the wrong definition of product. So, if I was indeed wrong in my definition of product in this context, could someone please give me the correct definition of product in this case?

-thewax-

Sorry, but I had to leave the word (space) there because the reply mechanism completely messed up my formatting.

-thewax-

7. Why is there no increase in product after 100 seconds?

"7. There is no increase in product after 100 seconds because all the enzymes are saturated and are already catalyzing reactions as fast as they can.

[/quote]

Maybe this will help to correct the answers.
When the reaction was going on there would be an increase in the product, but because this not the case it means that there is no substrate anymore.

-Gerard-

Thanks a lot, Gerard!!!!!!!!

So just to clarify things up a bit...
So are you saying that the solution key was wrong and that I was right????
So are you saying that the previous possible explanation that perhaps the enzyme was performing catalytic and anabolic pathways at the same time is not right???????
Can anyone confirm (or offer a different explanation or support a previously stated hypothesis) Gerard's conclusions???????????????

Any help on this issue would greatly be appreciated.
Thanks!

-thewax-

QUOTE (thewax @ Dec 23 2008, 01:28 PM)
Questions are excerpted from Deborah Goldberg AP Biology:

"Questions 5-11
. The product is measured in micrograms at 20-second intervals and recorded on the data table below.

Time(s) 0 (space) 20 (space) 40 (space) 60 (space) 80 (space)100 (space) 120
Product 0.0 (space)0.25 (space) 0.50 (space) 0.70 (space) 0.80 (space)0.85 (space) 0.85
(micrograms)

7. Why is there no increase in product after 100 seconds?

8. What would happen if you added only more enzyme after 100 seconds?

9. What would happen if you added only more substrate after 100 seconds?"

I know that this might seem like a homework question, when in fact this is NOT a homework question - I am trying to study for a big test soon by practicing on practice questions.

I will leave a bunch of space here so that your answers will not be influenced by the actual answers that I will type out below.

"7. There is no increase in product after 100 seconds because all the enzymes are saturated and are already catalyzing reactions as fast as they can.

8. Assuming there is excess substrate that enzyme is not colliding with, an addition of enzyme after 100 seconds would increase the rate of reaction until the enzyme, once again, became saturated.

9. If you add more substrate after 100 seconds, there would be no change because the enzyme is saturated and reacting with as much substrate as it can. The enzyme cannot handle any more substrate. If you added both substrate and enzyme after 100 seconds, the reaction rate would increase temporarily until the enzyme became saturated once again."

The work I did for this problem (as I did spend much time on this set of questions) is shown below.
I reasoned as follows: - Well the product is what was made, right? So if you look at times 100 and 120, you can clearly see that there was no increase in product (as question 7 pointed out). But that would mean that from 100 to 120, nothing was made, right (because once again the product is what you end up with, or, in other words, what you make)?????????? So it follows that (and this was my answer to question 7) there was no increase in product because, well, the reaction had finished, right????? So if you added more enzymes (question eight), no reaction would occur and you would still have the same amount of product (which was the substrate). It would also follow, then (question 9), that if you added only more substrate after 100 seconds, then the reaction would resume (as the one enzyme you had in the beginning would work again) and there would be more and more product until that reaction, too, was finished and then the product would remain the same.

Now, having explained my reasoning, can someone please explain to me why my reasoning was faulty???????????????? I'm not sure about this, but I have a hunch - I think that my reasoning fell apart, as after this step, my reasoning from there looks pretty good - I think that I assumed the wrong definition of product. So, if I was indeed wrong in my definition of product in this context, could someone please give me the correct definition of product in this case?

Why would you say the enzyme was saturated? For question 7, there is possiblity that all the substrates have been converted to product. If the measurement using colorimetic method, the product formation is cumulative. At the time 100, all subtrates converted to product, thus at 120 the amount of product will remain the same 0.85 ug because there are no more subtrates to be converted.

for question 8, since the subtrates are exhausted, the addition of enzyme would not increase the produt formation, it will remain 0.85 ug

for question 9, the addition of subtrates will show more formation of product, > 0.85 ug after time 100

For my opinion, the question should be like this 'In a lab experiment, one enzyme is combined with EXCESS substrate at time 0...........' in order to answer the way u answered.

I think I have gave plausible explaination. Correct me if I'm wrong

TQ

-kent19-