Peanut247
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Why does an increase in substrate not affect the rate of reaction when a non-competitive is present?

As surely as substrate increases, it would take longer for the inhibitors to "find" and collide with the enzyme even if it doesn't compete with the substrate Almost like the idea of decreasing the concentration of something?

Can someone please explain?:confused::confused:
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MarkProbio
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Well first of all, non-competetive inhibitors change the shape of the active site by binding to the enzyme away from the main active site. If the shape of the active site is changed too much then rate will stop altogether - I guess it depends on the example you are given.

Secondly, if you increase concentration of the substrate too much then there are so many substrates trying to "find" the active site that the active site is blocked regardless, so the rate of reaction would actually decrease after a certain point.

Does that help?
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Peanut247
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(Original post by MarkProbio)
Well first of all, non-competetive inhibitors change the shape of the active site by binding to the enzyme away from the main active site. If the shape of the active site is changed too much then rate will stop altogether - I guess it depends on the example you are given.

Secondly, if you increase concentration of the substrate too much then there are so many substrates trying to "find" the active site that the active site is blocked regardless, so the rate of reaction would actually decrease after a certain point.

Does that help?
Non competitive inhibitors change the shape of the active site I know, but they are reversible.
So when it comes out if the enzyme, if there is a high substrate concentration then wouldn't he likelihood of a substrate colliding with the enzyme be greater than a non competitive inhibitor colliding with the enzymes others site as there are a fewer number of them? They would mostly likely bump into a substrate instead so the inhibitor would take longer to find the enzyme to inhibit in a sea of substrate?
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MarkProbio
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(Original post by Peanut247)
Non competitive inhibitors change the shape of the active site I know, but they are reversible.
So when it comes out if the enzyme, if there is a high substrate concentration then wouldn't he likelihood of a substrate colliding with the enzyme be greater than a non competitive inhibitor colliding with the enzymes others site as there are a fewer number of them? They would mostly likely bump into a substrate instead so the inhibitor would take longer to find the enzyme to inhibit in a sea of substrate?
They aren't always reversible. So it depends on the example. I'm not sure of the exact biochemistry (I'm only A2 level) but I imagine the enzyme may stay that shape following the removal of the inhibitor.

It is true increased substrate increases rate, but remember there's always a point where all the enzymes' active sites are full, so it will no longer decrease. But inhibitors will change this somewhat.
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Peanut247
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(Original post by MarkProbio)
They aren't always reversible. So it depends on the example. I'm not sure of the exact biochemistry (I'm only A2 level) but I imagine the enzyme may stay that shape following the removal of the inhibitor.

It is true increased substrate increases rate, but remember there's always a point where all the enzymes' active sites are full, so it will no longer decrease. But inhibitors will change this somewhat.
If the enzyme active site stays th same shape then wouldn't eventually all the enzymes become inhibited? On a graph of substrate conc and rate, the graph levels off so that can't be the case?


I'm AS and they only expect us to know reversible
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MarkProbio
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(Original post by Peanut247)
If the enzyme active site stays th same shape then wouldn't eventually all the enzymes become inhibited? On a graph of substrate conc and rate, the graph levels off so that can't be the case?


I'm AS and they only expect us to know reversible
Are you on OCR? In my AS text book it says you need to know both and that irreversible non-competetive inhibitors practically denature the enzyme.
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Revenged
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Non competitive inhibitors are not affected by the amount of substrate.

Competitive inhibitors are affected by the amount of substrate.

It is the definition.
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Revenged
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(Original post by Peanut247)
Non competitive inhibitors change the shape of the active site I know, but they are reversible.
So when it comes out if the enzyme, if there is a high substrate concentration then wouldn't he likelihood of a substrate colliding with the enzyme be greater than a non competitive inhibitor colliding with the enzymes others site as there are a fewer number of them? They would mostly likely bump into a substrate instead so the inhibitor would take longer to find the enzyme to inhibit in a sea of substrate?
That would be a reversible competitive inhibitor.

A non-competitive, reversible or irreversible, is not affected by the agonist / substrate.
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