Enzymes Flashcards
What is the Michalis-Menten Model?
E + S ES –> E + P
V0 = Vmax [S]o / Km + [S]o
Km = [S] where vi = 1/2 Vmax
Why does Hexokinase have a low Km?
It will always work at Vmax, ensuring the RBC always has enough energy.
What do enzymes do?
They lower the activation energy to make the forward/backward reaction happen faster.
What are Irreversible Inhibitors?
The enzyme inhibitor binds so tightly, or covalently, the interaction is irreversible.
What happens to the graph in uncompetitive inhibition?
Shifts left. Km goes down and takes less substrate to reach Vmax (also decreases)
Which way will a negative allosteric effector shift the curve?
To the right
What does Vmax mean?
describes the maximal rate at which substrate can be converted to product when the enzyme is saturated
How can competitive inhibitors be reversed?
by increasing the substrate concentration.
What does a homoallosteric curve look like? Why?
Sigmoidal because molecules become more attracted to enzyme as they bind. (Positive homotropic)
What are heteroallosteric enzymes?
activator binds to the allosteric site to bring in the substrate for that enzyme
What happens to the graph in uncompetitive inhibition?
Shifts left. Km goes down and takes less substrate to reach Vmax.
What are allosteric enzymes? Allosteric = ?
these enzymes adopt different conformations in response to binding their substrates and allosteric modulators (effectors) = other shapes
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.
Do enzymes work without cofactors?
No, without cofactors they are called apoenzymes
What do protein kinases do? Are they specific or non-specific?
Phosphorylate and activate or inactivate regulatory proteins. Could be either.
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 are enzyme inhibitors?
Substances that interact with an enzyme and reduce the rate of the enzyme-catalyzed reaction.
Where is hexokinase found?
Present in all tissues except the liver and B cells of the pancreas
What is competitive inhibition?
Inhibitors compete for the binding site of the substrate.
Reversible Covalent Modification. Example?
allows for the coordinated response of several enzymes to a single signal. Phosphorylation of target proteins.
Irreversible inhibitors
bind extremely tightly to the enzyme or form covalent bonds and cannot be removed.
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 is uncompetitive inhibition?
Inhibitors bind the ES complex and inhibit catalysis. (Leo bound to orange and mitten)
What are homoallosteric enzymes?
exhibit cooperative substrate binding like Hb. (binds O2 to bring in MORE O2)
What are isozymes?
Different forms of enzymes
What does the rate of glucokinase depend on?
serum glucose once it reaches 5-8mM, Km is reached at 5mM
Where is glucokinase found?
Hepatocytes and B cells of the pancreas
Inactive precursors of some enzymes that are activated through hydrolysis reactions are called
zymogens
What is proteolytic cleavage reffering to?
Allows for the synthesis of proteins in a n inactive (proprotein, proenzyme, or zymogen) form. When the protein activity is physiologically needed, the zymogen undergoes proteolytic cleavage and is activated.
