Allosteric Enzymes Flashcards
What are allosteric enzymes
Enzymes that regulate the flow of biochemicals through stepwise metabolic pathways
They catalyze committed steps (ex. Biochemical A to B is a commited step and enzyme 1 catalyzes this step)
Have more than 1 subunit (quaternary structure)
More than 1 active site
What do the intermediates in the biochemical reaction do
Only move to eventual make F the final product
No other actual functions in the cell
What can allosteric enzymes bind to
Both stimulatory molecules and inhibitory molecules at its own regulatory sites (sites on the enzyme other than the active site)
What are inhibitory molecules
The final product in the pathway (F)
They bind to the regulatory site on the allosteric enzyme to DECREASE the activity
This signals that there’s enough product formed and turns off the biochemical pathway
What is feed forward activation for stimulatory molecules
The metabolite early on in the pathway binds to a regulatory site on an enzyme further down the pathway to signal an increase in substrate and increase the enzyme activity
Enhances production so the intermediate doesn’t build up
What type of kinetics do allosteric enzymes display
What are the two models that explain these kinetics
Sigmoidal (s shaped)
Concerted model
Sequential model
What is the concerted model for allosteric enzymes
The enzyme has many active site on the polypeptide chains
Has two forms: The relaxed (active) form catalyzes the reactions, the tense form is less active but more stable and common
The R and T forms are in equilibrium with each other
What is the allosteric constant for the concentred model
L0 = T/R
Typically in the hundreds
What is the symmetry rule for the concentred model
All active site of the enzyme must be in the same state (either all R or all T, no hybrids)
for the concentred model which form of the enzymes active site does the substrate bind more readily to
The r form not the t form
What is cooperativity for the concentred model
When the binding of substrate shifts the T and R form equilibrium in favour of R
When [s] is low what happens to the enzyme for the concentred model
The enzyme is in the stable tense T form
10:1 or T to R
When [s] increases what happens to the enzyme for the concentred model
The enzymes active site that were T get trapped in R form because the enzyme binds to an R form on the enzyme
Than as more energies become in are form more substrates bind and more enzymes go to R form
What is the threshold effect
The allosteric enzymes are more sensitive to changes in [S] near the Km value than michealis menten enzymes with the same Vmax
The menten enzyme needs more [s] increase to reach Vmax than the allosteric one
How does regulatory molecules regulate the activity of allosteric enzymes
Can be negative or positive regulators that bind to the regulatory site of the enzyme
Postive increase activity (ex. ATP)
Negative decreases activity (ex.CTP)
The regulators can shift the enzyme to the t state and make it more stable
