Flashcards in Enzymes pt. 1 Deck (53)
Enzymes are _____ specific for reactants (substrate)
What is a holoenzyme?
An enzyme WITH a cofactor; active
What is an apoenzyme?
An enzyme WITHOUT a cofactor; inactive
What are inorganic cofactors?
e.g. Zn2+, Mg2+, K+, etc.
What are organic cofactors?
Loosely bound, changed by reaction, derived from vitamins
What are the two types of organic cofactors aka conezymes?
Changed by reaction
Describe prosthetic groups
Tightly or covalently bound
Not changed by reaction
Can enzymes differ in their degree of specificity?
What is deltaG/ Gibbs free energy?
Energy of reactants - energy of products
Does deltaG give you any information about the rate of reaction?
What does deltaG tell you?
If a reaction is spontaneous (G less than 0) or non-spontaneous (G greater than 0)
How do you calculate deltaG?
deltaG = deltaG' + RT ln ([pdts]/[reactants])
or... [C]^c[D]^d / [A}^a[B]^b
What is deltaG'?
Standard free energy change
At equilibrium, deltaG = ?
At equilibrium, deltaG = 0, thus deltaG' = ______
deltaG' = -RT ln Keq
When Keq is greater than 1, _______ are favored and deltaG is ______ than zero
products, less than zero
When Keq is less than 1, _______ are favored and deltaG is ______ than zero
reactants, greater than zero
How do coupling reactions work?
They change the concentrations to make deltaG negative
How do enzymes lower the Ea?
Stabilizing the transition state
What does the transition state theory say?
The substrate and the transition species are in equilibrium
Keq = ?
Keq = e^(-Ea/RT)
Note, Ea also is deltaG of transition state
Relatively small changes in activation energy can lead to relatively ______ changes in overall reaction rate.
Because it is an exponent!
Once the fraction goes lower than the equilibrium fraction, free energy becomes _____ .
e.g. if [pdt]/[reactant] = 0.5 at equilibrium, a new ratio of 0.18 is LOWER and thus deltaG is NEGATIVE
What are common associations/non-covalent interactions in the active site of an enzyme?
Hydrogen bonds, Van der Waals interactions
What is the role of reversible non-covalent bonds in enzymes?
They can be used to release free energy (bind energy)
What are the 2 enzyme-substrate binding models?
1. Lock and key (highly specific and rigid)
2. Induced fit (enzyme changes shape and becomes complementary to substrate)
How do you achieve maximum binding energy between enzymes and substrates?
Multiple short range interactions
Which binding model is supported by data?