Lecture 21 Flashcards
What does Oligomeric mean?
Multi subunit
Can enzyme activity be cooperative?
Enzyme activity may be cooperative
What does the graph of a relationship between a substrate and reaction velocity look like if the enzyme activity is cooperative?
There is a sigmoidal relationship between substrate and reaction velocity
What is the activity like with allosteric enzymes?
The activity is cooperative
What is the sigmoidal relationship in allosteric enzymes a consequence of?
The equilibrium that exists between the low activity and high activity state of the enzyme
What compounds may affect the equilibrium between the T and R states with enzymes?
Compounds besides the substrate can affect equilibrium between the T and R states
What is an activator of an enzyme?
Something that binds to and stabilizes the R state/high activity state
What does something that stabilizes the R state do?
It makes the enzyme better at taking the substrate and turning it into product
What does something that stabilizes the T state do?
It makes the enzyme less able to convert the substrate into product
What does an inhibitor do?
It binds to an enzyme and stabilizes the T state making it less able to convert the substrate into product
What do the graphs of allosteric enzymes look like on reaction velocity substrate concentration curve?
The show a sigmoidal relationship
What does the binding curve of a non-allosteric enzyme look like?
It will have a hyperbolic binding curve
What does the sigmoidal curve of allosteric enzyme reflect?
- Increasing substrate results in increasing production of product
- substrate is a homoallosteric activator
What is an allosteric enzyme’s catalytic activity is modulated by?
The noncovalent binding of specific molecules at a site other than the active site
What does a negative heteroallosteric inhibitor do?
Binds to a regulatory site and changes the shape at the 4º and 3º level
What levels of structure do both homoallostery and heteroallostery change proteins?
3º and 4º structure
How does binding of an inhibitor affect an enzyme?
It changes the binding site of the enzyme making it unable to effectively bind the substrate
What are the two states of allosteric enzymes?
T (tense, low activity)
R (relaxed, high activity)
What state do allosteric activators favor?
They favor the R state
What state do allosteric inhibitors favor?
They favor the T state
What determines how much of the protein is in the T state and how much of the protein is in the R state at any given moment?
The balance of the substrate, any activators, any inhibitors and the protein
What does a sigmoidal relationship on a reaction velocity vs substrate concentration graph indicate?
That a substrate is a positive homoallosteric activator
What direction will a substance that decreases binding affinity shift the curve?
To the right
What will shift a reaction velocity vs substrate concentration curve to the left?
A positive heteroallosteric activator
