[4MANU4EVER4]

(Original post by Abbers)
Can someone explain the lock and key and induced fit model? And how they differ?

Yes...

The lock and key model is that the lock is analogous to the enzyme, and the key is analogous to the substrate. The substrate fits the enzyme in a complementary fashion but both are of a rigid shape.

The induced fit model is that the substrate induces a change in the conformation of the enzyme...(basically means that it alters its shape) and the enzyme is flexible to the substrate. (This is a more commonly accepted version.)

Hope this helped

[MediterraneanX]

Does anyone think a comparison of B-lymphocytes and T-lymphocytes might come up as one of the long questions at the end? They haven't really asked many questions about them in previous past papers other than talking about memory cells? I also think they're due a question on enzymes as a long question too (unless it came up in jan 2012 - can't remember) so maybe something to do with their protein structure?

[MediterraneanX]

(Original post by 4MANU4EVER4)
Yes...

The lock and key model is that the lock is analogous to the enzyme, and the key is analogous to the substrate. The substrate fits the enzyme in a complementary fashion but both are of a rigid shape.

The induced fit model is that the substrate induces a change in the conformation of the enzyme...(basically means that it alters its shape) and the enzyme is flexible to the substrate. (This is a more commonly accepted version.)

Hope this helped

I think you should look up the answer in one of the mark schemes as often they want you to say a specific word and though the answer above is correct, I'm not sure you'd get full marks with it as some of the key words aren't in it.

[4MANU4EVER4]

(Original post by MediterraneanX)
I think you should look up the answer in one of the mark schemes as often they want you to say a specific word and though the answer above is correct, I'm not sure you'd get full marks with it as some of the key words aren't in it.

Ok...this is from the jan 2011 biol 1 paper

2 (a) (i) Describe the induced fit model of enzyme action. (2 marks)

Mark Scheme Answer: (Any two from)

M1 Active site/enzyme not complementary
M2 Active site changes (shape)/is flexible (Allow binding site)
M3 (Change in enzyme allows) substrate to fit/ E-S complex to form

2 (a) (ii) Describe one way the lock and key model is different from the induced fit model. (1 mark)

Mark Scheme Answer: (Any one from)

M1 Active site does not change (shape)/is fixed (shape)/is rigid/does not wrap around the substrate/(already) fits the substrate/is complementary (before binding)


This is as accurate as it gets. First question requires "complementary" and second requires "active site".

Hope this helped.

[StudentAnon]

(Original post by 4MANU4EVER4)
Ok...this is from the jan 2011 biol 1 paper

2 (a) (i) Describe the induced fit model of enzyme action. (2 marks)

Mark Scheme Answer: (Any two from)

M1 Active site/enzyme not complementary
M2 Active site changes (shape)/is flexible (Allow binding site)
M3 (Change in enzyme allows) substrate to fit/ E-S complex to form

2 (a) (ii) Describe one way the lock and key model is different from the induced fit model. (1 mark)

Mark Scheme Answer: (Any one from)

M1 Active site does not change (shape)/is fixed (shape)/is rigid/does not wrap around the substrate/(already) fits the substrate/is complementary (before binding)


This is as accurate as it gets. First question requires "complementary" and second requires "active site".

Hope this helped.

Hold on.. so in the induced model the substrate is not complementary to the enzyme?

I thought it was, I know obviously it moulds its shape to fit the enzyme's active site but surely it is still complementary!

[MediterraneanX]

(Original post by StudentAnon)
Hold on.. so in the induced model the substrate is not complementary to the enzyme?

I thought it was, I know obviously it moulds its shape to fit the enzyme's active site but surely it is still complementary!

Careful - the enzyme changes its active site, the substrate doesn't change shape.

So no its not complimentary as the enzyme has to change its shape to become accommodate the substrate. In the lock and key model the substrate and active site perfectly compliment each other ie neither have to change shape to accommodate each other.

[thescientist17]

(Original post by YazB7)
Tbf I've given up on biology. I'd rather stick pins in my eyes than do a2. Unit 2 exam i'll be happy with an E, that's how bad it is

Oh no there is so much to learn though, so many little details. Well at least it'll all be over soon. What other subjects are you taking?

[StudentAnon]

(Original post by MediterraneanX)
Careful - the enzyme changes its active site, the substrate doesn't change shape.

So no its not complimentary as the enzyme has to change its shape to become accommodate the substrate. In the lock and key model the substrate and active site perfectly compliment each other ie neither have to change shape to accommodate each other.

Oops, I'll put that down to a temporary lapse haha.

And alright, never really thought about it but yeah I guess so, I'll be careful not to say they're complementary (in the induced fit model). The key thing is that the active site of the enzyme moulds to fit the shape of the substrate, and in doing so, lowers the activation energy of the substrate yes?

[MediterraneanX]

(Original post by StudentAnon)
Oops, I'll put that down to a temporary lapse haha.

And alright, never really thought about it but yeah I guess so, I'll be careful not to say they're complementary (in the induced fit model). The key thing is that the active site of the enzyme moulds to fit the shape of the substrate, and in doing so, lowers the activation energy of the substrate yes?

Yeah basically - what the other person posted (the mark scheme answer) will get you all the marks you need. I find with the enzyme questions they tend not to expect you to write it lowers the activation energy of the reaction. Just mention the enzymes active site must change its shape to compliment and bind with the substrate in order to form enzyme-substrate reactions. The bold words are the keywords they pretty much love you to use.

[thescientist17]

Guys this thread is looking dead! We need to encourage each other only 2 days to go!

[Monster Mnch]

Was hoping to get in a good weekend of top-up revision before the exam on Monday, but now I found out I got a family party to go to today, and then football tomorrow

[Jack_Smith]

(Original post by thescientist17)
Guys this thread is looking dead! We need to encourage each other only 2 days to go!

There more hatred of biology going on this thread than actually encouraging and asking questions! :/ (Im not fond of biology myself but still!)

[thescientist17]

(Original post by Jack_Smith)
There more hatred of biology going on this thread than actually encouraging and asking questions! :/ (Im not fond of biology myself but still!)

Exactly! I may have made a comment about how there is so much to learn and it can be a pain (not sure if it was in this thread or BIO2) but we can't change the fact that we have an exam in 2 days. So come on everyone, lets get asking questions, it could change our grade! Think positively!

[thescientist17]

Also explaining things to other people really helps me remember them in my opinion.

[thescientist17]

If anyone would like to explain co transport to me, they'd be a star! Or summarise the functions of the different cell organelles!

[Xiomara]

OK then, let's try and revive this thread :P

How can atheroma lead to aneurysm? (6 marks)

[shybrowngirl]

hey everyone, i know i made a thread about this. but i always get stuck on how to revise biology. like i went through so much past papers and most questions comes up again in different forms. so i made condensed notes using the specification from only mark schemes.... is this a good way to learn biology or not?

[hamzah190]

What are all the tests -
reducing sugars
non reducing sugars
lipid
etc?

[DavidH20]

(Original post by thescientist17)
If anyone would like to explain co transport to me, they'd be a star! Or summarise the functions of the different cell organelles!

Thescientist17,

Sodium Glucose cotransport is a form of active transport - essentially the carrier protein will not change its shape (allowing the substances across the membrane) unless both sodium and glucose bind. This kind of protein is called a symport (the protein for sodium-glucose cotransport is called SGLT-1 but I don't think you need to know that)

The opposite of a symport is an antiport - this is used in the sodium-potassium pump: sodium is transported one way whilst potassium is transported the other.

As for cell organelles, very briefly:

Nucleus: Control centre of cell, contains genetic information. Surrounded by the nuclear membrane.
Endoplasmic reticulum: site of chemical reactions such as protein synthesis or lipid metabolism. Can be rough (i.e. with attached ribosomes) or smooth.
Ribosomes: Site of protein synthesis
Golgi Apparatus: sorts and packages proteins into vesicles for secretion outside the cell.
Cell membrane: binds the cell and controls the substances entering and exiting
Mitochondria: site of respiration; produces ATP, the hydrolysis of which releases energy.
Microvilli: Provide a large surface area for diffusion/osmosis
Cytoplasm: matrix in which all metabolic activity of the cell occurs.
Lysosomes: Vesicles containing enzymes which can be used to digest unwanted organelles or pathogens.

Hope that helps, apologies if I've missed anything out.

[DavidH20]

(Original post by hamzah190)
What are all the tests -
reducing sugars
non reducing sugars
lipid
etc?

Hamzah190,

Test for reducing sugars is a benedict's test: add benedict's reagent and heat - if a reducing sugar is present it will turn brick-red.

The reason for this is that benedict's reagent contains aqueous Cu2+ ions in sodium hydroxide; if the anomeric carbon (i.e. the carbon in the sugar which is part of a double bond in chain form) is free to react, it donates an electron, making the Cu2+ ions into Cu+ ions, which react with the sodium hydroxide to form the brick-red precipitate of copper hydroxide.

Test for non-reducing sugars is the same; there will however be no precipitate. To check that it is a non-reducing sugar and not another molecule, you can heat with hydrochloric acid - this will hydrolise the glycosidic bonds and break up the non-reducing sugar into reducing sugars; the benedict's test will be positive if retested.

Test for proteins is a biuret test: very similar to benedict's test but with a different reagent. Add biuret's reagent and heat; if a protein is present a purple precipitate will form.

Lipid test is the emulsion test: The lipid should dissolve in ethanol, but when water is added, as fats and water are immiscible, the lipid will fall out of the solution and form a cloudy white emulsion which will be clearly visible.

Hope that all is accurate and helpful