Enzymes Flashcards
What do enzymes do?
They lower the activation energy to make the forward/backward reaction happen faster.
Do enzymes work without cofactors?
No
What is the Michalis-Menten Model?
E + S ES –> E + P
What does Vmax mean?
describes the maximal rate at which substrate can be converted to product
What is Km? Low Km? High Km?
It refers to the affinity of the sub to the enzyme. Low Km = high affinity. High Km = low affinity.
Where is glucokinase found?
Hepatocytes and B cells of the pancreas
Where is hexokinase found?
Present in all tissues except the liver and B cells of the pancreas
Why does Hexokinase have a low Km?
It will always work at Vmax, ensuring the RBC always has enough energy.
What does the rate of glucokinase depend on?
serum glucose
What are enzyme inhibitors?
Substances that interact with an enzyme and reduce the rate of the enzyme-catalyzed reaction.
Irreversible inhibitors
bind extremely tightly to the enzyme or form covalent bonds and cannot be removed.
How can competitive inhibitors be reversed?
by increasing the substrate concentration.
In competitive inhibition, When we add more substrate will Km increase or decrease? What about Vmax?
Increase, as more sub is added, graph shifts to the right. Vmax stays the same.
What is competitive inhibition?
Inhibitors compete for the binding site of the substrate.
What is uncompetitive inhibition?
Inhibitors bind the ES complex and inhibit catalysis. (Leo bound to orange and mitten)
What happens to the graph in uncompetitive inhibition?
Shifts left. Km goes down and takes less substrate to reach Vmax.
What happens to the graph in uncompetitive inhibition?
Shifts left. Km goes down and takes less substrate to reach Vmax (also decreases)
What is mixed (Noncompetitive) Inhibition? What will happen to Vmax/Km?
Inhibitor can bind to enzyme or ES complex. Vmax will decrease and effects on Km will vary.
What are Irreversible Inhibitors?
The enzyme inhibitor binds so tightly, or covalently, the interaction is irreversible.
What are allosteric enzymes?
Allosteric = ?
these enzymes adopt different conformations in response to binding their substrates and allosteric modulators (effectors)
= other shapes
What are homoallosteric enzymes?
exhibit cooperative substrate binding like Hb. (binds O2 to bring in MORE O2)
What are heteroallosteric enzymes?
activator binds to the allosteric site to bring in the substrate for that enzyme
What does a homoallosteric curve look like? Why?
Sigmoidal because molecules become more attracted to enzyme as they bind. (Positive homotropic)
Which way will a negative allosteric effector shift the curve?
To the right
