susiebe
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hi,

Ive just come across the following 2 mark question and feel a bit stupid to have been puzzling over it once I knew the answer!

Q.Galactose has a similar structure to part of the lactose molecule.
Explain how galactose inhibits lactase?

Is this a poorly worded question or should I have immediatly thought of galactose acting as a competitive inhibitor?
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Partypopcorn
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Could be worded a little better, but I think it’s just a case of practicing being able to spot what topic knowledge you need to apply 🙂
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susiebe
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Yes it mentioned the structure so i was thinking more about how its made up etc

Does galactose always inhibit lactase?
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susiebe
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(Original post by susiebe)
Yes it mentioned the structure so i was thinking more about how its made up etc

Does galactose always inhibit lactase?
Any further help appreciated.This q is still bugging me!
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susiebe
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Does anyone have an answer to this question?
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pineapple201
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(Original post by susiebe)
hi,

Ive just come across the following 2 mark question and feel a bit stupid to have been puzzling over it once I knew the answer!

Q.Galactose has a similar structure to part of the lactose molecule.
Explain how galactose inhibits lactase?

Is this a poorly worded question or should I have immediatly thought of galactose acting as a competitive inhibitor?
I don't have the mark scheme with me, but the answer will almost definitely involved it being a competitive inhibitor and forming an enzyme-substrate complex with the lactose molecule, blocking the lactase enzyme from binding. The galactose will bind because it's complementary to the specific active site.

I've seen this question come up MANY times in tests and it's important to mention 3 key phrases
1) Specific active site, complementary substrate shape
2) Enzyme substrate complexes
3) Where it binds (enzyme's active site or elsewhere)

Sorry for being extra, Biology is really annoying at times and you have to get all the little things right because once you get to A2, they expect you to mention a lot more for 1 mark!
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susiebe
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(Original post by pineapple201)
I don't have the mark scheme with me, but the answer will almost definitely involved it being a competitive inhibitor and forming an enzyme-substrate complex with the lactose molecule, blocking the lactase enzyme from binding. The galactose will bind because it's complementary to the specific active site.

I've seen this question come up MANY times in tests and it's important to mention 3 key phrases
1) Specific active site, complementary substrate shape
2) Enzyme substrate complexes
3) Where it binds (enzyme's active site or elsewhere)

Sorry for being extra, Biology is really annoying at times and you have to get all the little things right because once you get to A2, they expect you to mention a lot more for 1 mark!
Thank you!
I'm trying to learn those phrases and also fit them into my answers.

However the reason I'm finding this q tricky is because I know lactose and galactose are sugar molecules and lactase is an enzyme.
So how do lactose and galactose bind and form a ESC?
I wasn't aware that they had an active site.

My understanding is that the inhibitor binds to an enzyme which stops the substrate from being able to bind, either that its filling the active site (competitive) or its binding elsewhere on the enzyme and causing the active site to change shape (non-competitve)
Its thrown me by talking about lactose and galactose binding!

Any further explanation most welcome!
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pineapple201
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(Original post by susiebe)
Thank you!
I'm trying to learn those phrases and also fit them into my answers.

However the reason I'm finding this q tricky is because I know lactose and galactose are sugar molecules and lactase is an enzyme.
So how do lactose and galactose bind and form a ESC?
I wasn't aware that they had an active site.

My understanding is that the inhibitor binds to an enzyme which stops the substrate from being able to bind, either that its filling the active site (competitive) or its binding elsewhere on the enzyme and causing the active site to change shape (non-competitve)
Its thrown me by talking about lactose and galactose binding!

Any further explanation most welcome!
Sorry that's a mistake on my end! I meant to say that glactose binds to the lactase and stops the lactose from binding. You're understanding is perfect
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susiebe
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(Original post by pineapple201)
Sorry that's a mistake on my end! I meant to say that glactose binds to the lactase and stops the lactose from binding. You're understanding is perfect
Aaah thank you!!
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