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1

Enzymes are _____ specific for reactants (substrate)

highly

2

What is a holoenzyme?

An enzyme WITH a cofactor; active

3

What is an apoenzyme?

An enzyme WITHOUT a cofactor; inactive

4

What are inorganic cofactors?

Metal ions
e.g. Zn2+, Mg2+, K+, etc.

5

What are organic cofactors?

Aka coenzymes

Loosely bound, changed by reaction, derived from vitamins

6

What are the two types of organic cofactors aka conezymes?

Co-substrate

Prosthetic group

7

Describe co-substrates.

Loosely bound
Changed by reaction

8

Describe prosthetic groups

Tightly or covalently bound
Not changed by reaction

9

Can enzymes differ in their degree of specificity?

Yes

10

What is deltaG/ Gibbs free energy?

Energy of reactants - energy of products

11

Does deltaG give you any information about the rate of reaction?

No!

12

What does deltaG tell you?

If a reaction is spontaneous (G less than 0) or non-spontaneous (G greater than 0)

13

How do you calculate deltaG?

deltaG = deltaG' + RT ln ([pdts]/[reactants])

or... [C]^c[D]^d / [A}^a[B]^b

14

What is deltaG'?

Standard free energy change

15

At equilibrium, deltaG = ?

zero

16

At equilibrium, deltaG = 0, thus deltaG' = ______

deltaG' = -RT ln Keq

17

When Keq is greater than 1, _______ are favored and deltaG is ______ than zero

products, less than zero

18

When Keq is less than 1, _______ are favored and deltaG is ______ than zero

reactants, greater than zero

19

How do coupling reactions work?

They change the concentrations to make deltaG negative

20

How do enzymes lower the Ea?

Stabilizing the transition state

21

What does the transition state theory say?

The substrate and the transition species are in equilibrium

22

Keq = ?

Keq = e^(-Ea/RT)

Note, Ea also is deltaG of transition state

23

Relatively small changes in activation energy can lead to relatively ______ changes in overall reaction rate.

Large!

Because it is an exponent!

24

Once the fraction goes lower than the equilibrium fraction, free energy becomes _____ .

Negative.

e.g. if [pdt]/[reactant] = 0.5 at equilibrium, a new ratio of 0.18 is LOWER and thus deltaG is NEGATIVE

25

What are common associations/non-covalent interactions in the active site of an enzyme?

Hydrogen bonds, Van der Waals interactions

26

What is the role of reversible non-covalent bonds in enzymes?

They can be used to release free energy (bind energy)

27

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)

28

How do you achieve maximum binding energy between enzymes and substrates?

Multiple short range interactions

29

Which binding model is supported by data?

Induced fit

30

How is free energy (binding energy) released?

By the formation of weak interactions from the induced fit of enzyme and substrate