Lecture 10: Control of Enzyme action Flashcards
Describe the graph for enzyme reaction rate vs temperature
As temperature increases, enyzme reaction rate increases up to an optimum which afterward the enzyme becomes unstable and denatures and this causes reaction rate to drop off rapidly
How does the presence of a single ionising amino acid vs two (a positive and negative) affects a proteins sensitivity to pH and what do the graphs look like
In order for the active site of a protein to work properly an enzyme might need a certain charged groups. Therefore as the pH increases over the pKa of the group the reaction rate can increase depending on whether the acid or base form is required for the enzyme to be functional. This graph is a single half of a bell whereas for 2 ionisable acids the optimum pH is more central on the side of the pKas so it makes a bell shape
Define the homotropic effect
This is when the binding of substrate to one active site on the enzyme changes the affinity of other active sites for substrate (Km) through triggering conformational change in the subunits from high Km to low Km of the enzyme leading to faster reaction rate.
How does subunit interaction lead to sigmoidal concentration dependence in the rate of reaction (v) of a multi unit enzyme
Cooperativity in the system means that with the increase in substrate concentration, the rate can suddenly increase dramatically like a switch
What is the hill plot and what do you find from it
A straight line graph using log of the rate of reaction. The slope of the line is h, the hill coefficient. The x intercept is log K/ h
How do you find the Vmax, K, and h from a V vs [S] graph
The last portion of the graph at the top of the S where it levels out is Vmax. The slope of the line is h and the [S] at half of Vmax is K
What is h
Hills constant, which shows the degree of cooperativity in this system
What is heterotropic effect
Allosteric enzymes are sensitive to modulation by non substrate molecules that act as heterotropic effectors such as inhibitors (negative) or activators (positive). These cause changes in he affinity of the other subunits for substrate
How is heterotropic effect used in metabolic pathways
The first enzyme in the pathway is often allosterically regulated. The end product of the metabolic pathway is often a negative heterotropic effector for the first enzyme in the pathway.
What is the biological importance of Allosteric enzymes
They can act as switches as the rate of reaction is very sensitive to [S]
What is the rate of reaction for a homotropically regulated enzyme
v= Vmax + [S]^ hills constant / K + [S]^ hills constant
Does Homotropic allostery increase the Km or decrease it (positive effect)
it decreases the Km of the other subunits
