ENZYME ACTION

Question 1

*What is an enzyme ? Provide an example of an important reaction that requires an enzyme (CO2)

Answer 1

Enzyme- protein catalyst that speeds up a reaction
When water reacts with CO2, the enzyme carbonic anhydrase (one of fastest enzymes) allow reaction to occur and produce carbonic acid in red blood cells. (OH-O=C-OH).

Question 2

What are substrates?

Answer 2

the reactants in an enzyme catalyzed reaction.

Question 3

What is the function of Proteolytic enzymes? Provide examples of these proteolytic enzymes and discuss their specificity.

Answer 3

Proteolytic enzymes- catalyze hydrolysis of peptide bonds (break peptide bond by adding H2O and form Carboxyl and amino groups)
Ex: Trypsin and Papain have different degrees of specificity.
Trypsin- specific to catalyze hydrolysis on Lysine or Arginine residues
Papain- not as specific. will cleave any peptide bond (papaya plant)
Thrombin- more specific than trypsin; ONLY catalyze on ARG-GLY bonds. used in blood clotting.

Question 4

What are the six major classes of enzymes?

Answer 4

1. Oxidoreducatase- oxid-reduc reactions (transfer e-)
2. Transferases -move fcn groups between molecules
3. Hydrolases- cleave bonds with adding H2O
4. Lyases- remove atoms to form double bonds/add to db.
5. Isomerases- move fcn groups within molecule
6. Ligases- join two molecules using ATP

Question 5

What are cofactors? what are the two types? What are prosthetic groups?

Answer 5

Cofactors- small molecules that some enzymes require for activity. Can be coenzymes (derived from Vitamins) and metals Ex: FAD, NAD+; Zn, K+
Prosthetic groups- tightly bound coenzymes.

Question 6

Distinguish between holoenzyme and apoenzyme

Answer 6

Holoenzyme- enzyme with cofactor

Apoenzyme- enzyme without a cofactor (inactive)

Question 7

What are the thermodynamic properties of a reaction

Answer 7

1. free energy difference (delta G) between reactants and products determines whether reactions occur spontaneously.
2. energy required to initiate conversion of reactant to products determines the rate of reaction (how enzymes involve)

Question 8

*What is Free energy (G)? How does delta G apply to enzymes?

Answer 8

measure of energy that is capable of doing work. enzymes do not alter change in free energy (delta G)

Question 9

distinguish between exergonic and endergonic reactions. which is spontaneous? What is the sign of delta G?

Answer 9

Exergonic reactions- reaction that will occur spontaneously (w/out input of energy), Delta G is negative.
Endergonic reactions- reaction will NOT occur spontaneous (need an input of energy to drive reaction) Delta G is positive

Question 10

Describe what occurs when Delta G= 0

Answer 10

when Delta G=0, the reaction is at equilibrium. There is not net change in concentrations of reactants and products. Reaction has stopped.

Question 11

What kind of info does delta G depend on? What does it not depend on?

Answer 11

Delta G depends only on free energy difference between reactants and products.
Does NOT have info on how reaction occurs, or rate of reaction

Question 12

What happens when the pka is less than pH?

Answer 12

the compound will be protonated and there will be more of reactant present.

Question 13

What does the pka tell you? What other info does this provide?

Answer 13

tells you pH that the chemical group needs to be to accept or donate an proton. Hence it lets you know how acidic or basic a group is.

Question 14

Describe the relationship between acidity and pka.

Answer 14

the lower the pka, the stronger the acid and greater the ability to donate protons (vice versa)

Question 15

What is Delta G ?

Answer 15

The change in free energy when a reaction occurs.

Question 16

*What is Delta G^o? What does it tell you?

Answer 16

The standard free energy change of reaction (change in energy of reaction under standard conditoins). The special conditions for reaction when concentrations of reactants and products are each 1 molar, pH of 7.

Question 17

*What is the free energy change equation? what do the symbols represent?

Answer 17

Delta G= Delta G^o + RT ln [ C ] [ D ]/ [ A ] [B ]

R- gas constant, T- Kelvins.

Question 18

How does standard free energy change relate to equilibrium constant (K’eq)

Answer 18

At equilibrium, delta G= 0, making energy equation 0= delta G^o + RT ln [ C ] [ D ]/ [ A ] [B ] which = Delta G^o = -RT ln [ C ] [ D ]/ [ A ] [B ].
k equilibrium constant for reaction under standard conditions:
K’eq= [ C ] [ D ]/ [ A ] [B ] and can be substituted for concentration of products and reactants in free energy change equation.
So K’eq= e^-delta G/RT (RT = 2.47)

Question 19

How do exergonic and endergonic reactions relate to equilibrium?

Answer 19

The more exergonic a reaction, the LARGER the keq.

The more endergonic a reaction, smaller the keq.

Question 20

What determines the differences between Delta G and Delta G^o?

Answer 20

Delta G can be larger than, smaller or equal to delta G^o depending on concentrations of reactions.

Question 21

*How does standard free energy change (Delta G^o) relate to keq? in terms of products vs substrate?

Answer 21

The larger the standard free energy change, the smaller the keq, and you will have more substrate than products.

smaller the G^o, larger keq and more products than substrate.

Question 22

What Factor from free energy change equation is criteria for spontaneity of reaction?

Answer 22

Delta G only (not standard free energy)

Question 23

*What is equilibrium? What determines this reaction equilibrium?

Answer 23

Equilibrium- when there is no net change in concentration of products and reactants, delta G =0.
only determined by the free energy difference between the products and reactants.
enzymes do not change equilibrium.

Question 24

*What is the transition state in a reaction? What facilitates forming of transition state?

Answer 24

The point in the middle of reaction that is after the substrate but has not yet become product.
transition state X^$- has double dagger sign.
Enzymes facilitates this.

Question 25

*What is the activation energy?

Answer 25

Energy required to form the transition state from substrate (delta G$) (delta G$= Gx^$ - Gs)

Question 26

How do enzymes affect the transition state?

Answer 26

Enzymes will reduce the energy needed to form transition state (Activation energy) and allow the reaction to go faster.

Question 27

*What is the first step of Enzyme catalysis?

Answer 27

forming the enzyme- substrate complex

Question 28

What promotes the transition state?

Answer 28

the interaction of the enzyme and substrates at the active site. (enzyme and S come together to form ES complex at active site)

Question 29

Describe features of the active site on enzymes.

Answer 29

1. 3D cleft or crevice created by amino acids from different parts of primary structure
2. constitutes a small portion of enzyme volume
3. sites create microenvironments.
4. multiple weak interactions (noncovalent) between enzyme and substrate interactions
5. enzyme specificity depends on molecular architecture (shape) of active site.

Question 30

How do enzymes interact with their substrates? What is this type of interaction called.

Answer 30

Enzyme will change shape upon substrate binding to active site on enzyme.
INDUCED FIT
(enzyme and substrate, NOT lock and key)

Question 31

*What is the binding energy in a reaction? When is binding energy highest?

Answer 31

The free energy released from interaction between enzyme and substrate.
binding energy highest when enzyme interacts with transition state, and will thus facilitate formation of transition state.

Question 32

What is the stability of istate and why?

Answer 32

least stable because it has the highest free energy in reaction compared to substrate and products.

Question 33

What is the essence of catalysis?

Answer 33

to stabilize the transition state?

Question 34

What happens to reaction when activation energy is lower?

Answer 34

Activation energy lower, more molecules have enough energy to reach transition state, and you’ll make products faster.

Question 35

*What are transition state analogs? How are they useful?

Answer 35

compounds that resemble transition state of reaction but are not actually acted upon by enzyme. They serve as inhibitors for enzyme catalyzed reactions since they can bind so tightly to an enzyme even more than substrate.

Question 36

What are abyzymes?

Answer 36

Antibodies that serves as enzymes and recognize transition states.