Enzymes Flashcards
What is the transition state?
High energy intermediate that lies between S and P
What is the activation energy?
Minimum energy S must have to allow reaction
What is the active site?
The place where substrates bind and where the chemical reaction occurs. Formed by amino acids from different parts of the primary sequence. They are clefts or crevices that have a complementary shape to the substrate
What is Vmax?
Maximal rate when all enzyme active sites are saturated with substrate
What is Km?
Substrate concentration that gives half the maximal velocity (units of concentration)
What does low km give rise to?
High affinity for substrate
What does high km give rise to?
Low affinity for substrate
What are Vmax values measured in?
Measured In amounts per unit time
1 unit is the amount of enzyme that converts one micromole of product per minute under standard conditions
What are competitive inhibitors?
These bind to the active site of an enzyme
Competes with substrate
Affects Km not Vmax
What are non competitive inhibitors?
Binds at another site on the enzyme, not active site
Affects Vmax not Km
How does temperature increase the rate of reaction?
Increases number of molecules with activation energy
How does concentration increase the rate of reaction?
Increases chance of molecular collisions
Other than lowering activation energy, how else do enzymes increase the rate of reaction?
Provides a platform for molecules to react so increases the chance of collisions.
What are some important features of enzymes?
Highly specific, unchanged after reaction, do not affect equilibrium, increase rate of reaction
What is the induced fit hypothesis?
Binding of substrates to an enzyme can induce changes in the conformation - the active site only forms a complementary shape after binding of the substrate
How are substrates bound to active sites?
By multiple weak bonds
When reaction rate is shown as a function of substrate concentration, what is usually the shape of the graph?
Rectangular hyperbola (the reaction reaches a maximum velocity)
What is the Mchaelis-Menten equation and what does it predict?
V0 = Vmax[S] / Km + [S]
V0 - initial velocity
Predicts that a plot of V0 vs substrate concentration will be a rectangular hyperbola
For example, if Hexokinase has a Km of 0.1 mM and Glucokinase has a Km of 5 mM, which has a higher affinity for it’s substrate (glucose) ?
Hexokinase - hence why HK is always active whereas GK only becomes active when glucose levels peak after feeding
What are reversible inhibitors?
Non-covalent, can freely dissociate (competitive and non competitive)
What is one unit in enzyme kinetics?
1 unit = the amount of enzyme that converts 1 micro mol of product per minute under standard conditions
The Michaelis-Menten equation can be rearranged to give a linear plot in the from y = mx + c. What is this?
y = mx + c
1/V0 = (Km/Vmax * 1/[S]) + 1/Vmax
Therefore intercept = 1/V0
Gradient = Km/Vmax
What are irreversible inhibitors?
Bind very tightly, generally form covalent bonds
What is an example of an irreversible inhibitor?
Nerve gases such as sarin (interferes with degradation of acetylcholine at neuromuscular junctions - inhibitor of acetylcholinesterase)
Which type of inhibitor affects Km?
Competitive
Which type of inhibitor affects Vmax?
Non-competitive
What overcomes the effect of competitive inhibitors?
Adding enough substrate
Why does Km increase with competitive inhibition
Because the inhibitor competes with the substrate for the active site so Km increases
Assuming the Km values of ethanol and methanol are 1 mm and 10 mM respectively, explain why giving ethanol to a patient with methanol poisoning would be beneficial.
Ethanol has a lower Km value than methanol so the enzyme has a higher affinity to ethanol than to methanol. Therefore, more ethanol will bind to the enzyme than methanol.
What are zymogens?
Inactive precursors of enzymes
