[boxxy27]

hey well im new to this forum, and i got like 2 days to finish this project of mine. The only thing is that i am really bad at finding stuff about chemistry online which lead me to a forum. Anyway, i know you guys are like pros at this stuff but i need help on explaining what;

Heterogeneous/Homogeneous Diagrams Are for the catalyst Palladium.....cause i cant find it anywhere
and
What a Lock + Key / Induced Fit Diagrams Are? and this is for the enzyme Amylase

I'm completely stuck when it comes to this so if anyone could help out it would be great thanks

[Sam (NG)]

Do you understand the terms heterogeneous and homogeneous catalysis?  I've never heard of "Heterogeneous and Homogeneous Diagrams"  unless i've just never heard them named like that before.

The lock and key principle and induced fit principles are to do with the shape of the active site of enzymes.  Lock and key suggests that there is a specific shape of each substrate and the active site of a catalyst (amylase) is fixed, with only one substrate molecule fitting that active site (like a key in a lock).  The induced fit system is more accurate and suggests that upon binding of the substrate to form the enzyme substrate complex, the shape of the active site changes to fit the shape of the substrate, although the substrate has to be roughly the same shape to begin with.

That's how i was taught those hypotheses in High School Biology, other people may offer better explanations.

[edit] I've found a  diagram of heterogeneous catalysis, but i don't think i've ever seen a similar diagram for the homogeneous case:

[boxxy27]

Um thanks man for the quick reply...

Even though im still a little confused of your explanation of the lock and key/induced fit description i just have to research a little more on that. Anyhow, what do you think is the best link/site to go for, for this information?

[Yggdrasil]

I'll try to provide an explanation:

Biological catalysts (enzymes) have a very high specificities.  Enzymes will bind to and very specific molecules and are able to recognize very subtle differences.  For example, the cellular machinery will only recognize L-amino acids, but not D-amino acids, which are just the mirror images of the L-amino acids. 

To explain the extraordinary selectivity of enzymes, Emil Fischer proposed a "lock and key" model to describe enzymes.  The substrates of an enzyme are like keys and the enzyme is like a lock.  Only a certain key with a specific sets of grooves and knotches is able to fit into the lock, turn, and open the door.  Similarly, Fischer proposed that only a specific substrate with its unique arrangement of functional groups would be able to fit into the enzyme active site and undergo catalysis.

While a lot of research on enzymes did support this model, some evidence began to arise that the model was incomplete.  For example, the lock and key model suggests a static picture, that the enzyme is an unmoving object.  About half a century after Fischer proposed the lock and key model, Daniel Koshland proposed a modification to the lock and key model.  By then it was apparent that enzymes were not unmoving objects, but rather that enzymes could undergo conformational change (change in shape).  So, he proposed that after recognizing its substrate, the binding of the substrate to the enzyme would trigger a conformational change which would move key parts of the enzyme around the substrate.  This conformational change would both strengthen binding and position functional groups on a protein for catalysis.  Koshland called this model the "induced fit" model.

I like to think of the induced fit model in analogy to baseball (sorry if you are not American).  Think of the substrate as the baseball and the enzyme as the glove.  When the baseball hits the glove, the player closes the glove around the ball as he catches it.  Similarly, when the substrate binds to the enzyme, the enzyme clamps on to the substrate and primes it for catalysis. 

There are many examples of enzymes which fit into the induced fit model.  For example, hemoglobin undergoes conformational change when it binds oxygen.  Another really cool example is ATP synthase, where the conformation change is linked to a rotating "axel" driven by proton transport.