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Enzyme function also depends on __.

pH. Important for enzyme conformation


The enzyme that functions in your stomach has an optimum pH of __.

2. That's where it's most active


Why does the stomach become acidic during digestion?

It's all about the digestion of protein. The stomach is for the digestion of protein. Which is typically in a globular form. A globular form is hard to digest. So you change the pH drastically so the enzyme denatures...and now the hydrolyses can now cut the protein because it's vulnerable.


The situation when a molecule is blocking the active site is called _________ _________.

competitive inhibition


If a molecule binds to an allosteric site, it changes the shape of the enzyme, which...

turns the enzyme off. It changed the shaped. Structure determines function.


Competitive inhibition involves an _______ site.



Noncompetitive inhibition involves an _________ site.

allosteric, means "other shape"


Allosteric regulation can either work _______ OR _______.

positively or negatively


If it's negative, we call that __________ __________.

noncompetitive inhibition


Which one may be countered by increasing substrate concentration? Competitive inhibition or noncompetitive inhibition?

Competitive inhibition. If the inhibition is working this way...**adding more substrate can outcompete the inhibitor.**


In biology, when we say "two molecules bind,"...they also _____ _____. Remember, weak interactions are ________. Bind, come apart, bind, come apart. Yes, the inhibitor is binding and blocking the active site, but a moment later it will come off. And if there's more substrate, guess who's going to bind next? Substate and not the inhibitor. It is possible to outcompete the inhibitor by adding more substrate.

come apart, reversible


Do all enzymes have active sites?

Every enzyme has an active site, it's not an enzyme without an active site


Do all enzymes have allosteric sites?

NO, that's going to depend on the enzyme.


What is the regulatory molecule?

You get a snake bite and the poison might be the inhibitor.
The inhibitor might be something that's already in your body that's blocking the active site.


Is it necessary to regulate all the enzymes of a pathway?
Lets say we have a pathway with 5 enzymes...if we want to shut this pathway off, must we inactivate all 5 enzymes? How could we do this in a more efficient way?

There's a mechanism to shut off a pathway. An entire pathway...using the final product of the pathway. Shut off a pathway using the final product. This is referred to as *FEEDBACK INHIBITION.*


Isoleucine is made from threonine in __ steps.



It takes 5 steps to make isoleucine.
Enzyme #1 has an ________ site. The allosteric site is complementary to the shape of isoleucine. So isoleucine can bind to that enzyme, and inhibit it. What's the effect on that binding inhibition?

allosteric. You turn off the enzyme.


What happens if you shut off enzyme one?

You no longer make your product.


So we've shut off an entire pathway through the _______ of that pathway, which ______ back either the first enzyme or a very early enzyme in the pathway. This is called _______ inhibition.

product, feeds, feedback


By turning off key enzymes, you can shut down entire _______.



Where an enzyme is ________ can affect the rate of an enzyme catalyzed reaction



Describe three ways that cells localize their enzymes for more efficient functioning in metabolic pathways

1) In organelles
2) As membrane proteins
3) In multi-enzyme complexes


ATP hydrolysis can be COUPLED to an endergonic reaction to make that reaction happen. For example, an unfavorable reaction with a delta G of ____ could be driven (or fueled) by a mole of ATP.
a) +5.5 kcal/mole
b) +8.0 kcal/mole
c) -14.6kcal/mole
d) -7.3 kcal/mole
e) 0 kcal/mole

+5.5 kcal/mole. The delta g of ATP hydrolysis - an exergonic reaction - is -7.3 kcal/mole. ATP hydrolysis can be used to fuel an endergonic reaction - one with a positive delta G - that requires LESS THAN 7.3 kcal/mole


During coupling, HOW is ATP actually used to make a reaction happen?

A phosphate is transferred from ATP to a reactant.


_________ is the basic mechanism by which ATP is used to do work.



Either a _______ or a ______ may be phosphorylated.

reactant or a protein


In steps _ and _ of glycolysis, phosphorylation is used to boost the energy of metabolic intermediates.

1 and 3


How exactly does ATP drive the sodium-potassium pump?

A phosphate is transferred from ATP to the pump


Does allosteric regulation STIUMULATE or INHIBIT an enzyme's activity?

Either stimulates or inhibits


Isoleucine biosynthesis is regulated by FEEDBACK INHIBITION; an early step of its metabolic pathway is blocked at high concentrations of _________.