Unit 1 - Lecture 7

Proteins

Enzymes are usually __

Catalytic RNA (Ribozymes)

What enzymes are not proteins?

Catalysts

Enzymes are excellent __

Increase

Enzymes __ rates of reaction under very mild conditions in aqueous solution

Enzymes

Allow biomolecules and metabolites to be synthesized and degraded under physiological conditions, where otherwise the chemical reactions would not proceed at a meaningful rate

Cofactors

In many enzymes the catalysis is accomplished by the protein alone. In others the activity requires __

Do

Enzymes are classified according to what they __

Oxidoreductases

Type of enzymes that transfer electrons

Transferases

Type of enzymes that have group transfer

Hydrolases

Type of enzymes that are involved in hydrolysis reactions

Lyases

Type of enzymes that add groups to double bonds or form double bonds by removal of groups

Isomerases

Type of enzymes that transfer groups within molecules to yield isomeric forms

Ligases

Type of enzymes that catalyze the joining together of two molecules, coupled with the hydrolysis of ATP

Substrates

Enzymes are highly specific for their __

Substrate; S

In an enzyme-catalyzed reaction : __ (__) is a reactant

Product; P

In an enzyme-catalyzed reaction : __ (__) is a result of the reaction

Active Site

The portion of the enzyme to which the substrate binds and where the reaction takes place

Noncovalent

What type of force (bond) occurs at the active site between the enzyme and substrate?

Hydrogen Bonding

Electrostatic Attractions

Van Der Waals Attractions

What are three examples of noncovalent forces?

Speed; Alter

Enzymes can __ up reactions but cannot __ the equilibrium constant or the free energy change

Free Energy Change

ΔGo is the standard __ for reactants (R) → products (P) under standard conditions

Products; Reactants

An enzymes reaction favors __ since its free energy is lower than the __

Activation Energy

ΔGo‡ is the __ of the reaction

• Even though the reaction is favorable, it will not proceed due to this activation energy barrier

Uncatalyzed; Catalyzed

ΔGo‡ for an __ reaction is higher than that for a __ reaction

Activation Energy

ΔGo‡ represents what?

Lowering

Enzymes catalyze reactions by __ the activation energy (ΔGo‡) of the transition state

Don’t

Enzymes __ determine the direction of a reaction or change the equilibrium

Unchanged

Catalysts remain __ before and after the reaction

Complementary

All enzymes are __ to their transition states

1) By stressing, bending, or stretching critical chemical bonds

2) By directly participating in the reaction

3) By creating a microhabitat that is conducive to the reaction

4) By simply orienting substrate molecules in place so that they can be modified

An enzyme can reduce the activation energy in what four ways?

1) General acid-base catalysis

2) Covalent catalysis

3) Metal ion catalysis

What 3 common catalytic strategies do enzymes employ?

General acid-base catalysis

What type of catalysis : often the enzyme provides additional functional groups that aid in catalysis once the substrate is bound

• General acids and bases are some of the most important contributors

Covalent Catalysis

What type of catalysis : is characterized by the formation of a covalent bond between the enzyme and substrate at some point during catalysis and must be broken later in the catalytic cycle in order to release product and regenerate the free enzyme

Multiple

Enzymes can employ __ catalytic strategies

Metal Ion Catalysis

What type of catalysis : have __ with positive charges that stabilize negatively charged transition states

1/3

About __ of all enzymes use metal ions

Equilibrium Constants

Enzymes are controlled by __

Enzyme

Equation : E + S → ← ES → ← EP → ← E + P

E represents what?

Substrate

Equation : E + S → ← ES → ← EP → ← E + P

S represents what?

Products

Equation : E + S → ← ES → ← EP → ← E + P

P represents what?

Equilibrium

The equation E + S → ← ES → ← EP → ← E + P is for what?

Keq

Change in free energy is related to the equilibrium constant __

Right; Not Proceed

In the overall equilibrium S → ← P, if [S] is high, the reaction is driven to the __. If [S] is too low, the reaction will __

Substrate Concentration

Rate of a reaction with an enzyme is dependent on __

Low

At __ substrate concentration Vo increases almost linearly with increasing [S]

Initial Velocity

Vo represents what?

High

At __ substrate concentration the rate reaches a maximum, Vmax

Enzyme Substrate

ES represets what?

Slow; Rate-Limiting

The breakdown of ES to form E + P is the __ step and hence __

Michaelis Menton Equation

This is a simple algebraic relationship between the substrate concentrations and initial rate (Vo)

1. The concentration of the k-2 product is negligible and can be ignored

2. [ES] is constant

What are the two assumptions are associated with the Michaelis Menton Equation

Steady State

ES is constant and is considered to be the __

Rate Constants

k1, k-1, k2 and k-2 in the Michaelis Menton Equation are __ for individual steps

ES

In the Michaelis Menton Equation, the Vo is determined by the rate of breakdown of __ to form product

Hyperbolic

The Michaelis Menton Equation equation describes a __ function

1/2

When [S] = Km, Vo = __ Vmax

Km

__ is equal to the concentration of substrate at 1/2 Vmax

Km

__ is an indication of how tightly an enzyme binds substrate

Lower; Higher

The __ the Km, the tighter binding (higher affinity) while a __ Km suggests weaker binding (lower affinity)

Rate Limiting

Initial velocity is controlled by a __ step

Kcat

What is used to reference the generic rate limiting step

Turnover Number

kcat is a rate constant (time-1) that is often called the __

Diffusion

Very efficient enzymes are limited by the rate of __

pH; Temperature

Enzymes activities are dependent upon __ and __

Kcat/Km

The catalytic efficiency equation is written as what?

Michaelis Menton Equation

What is being shown?

Michaelis Menton Equation with a rate-limiting step

What is being shown?

Reactants

1

Transition State

2

Free Energy of Activation (ΔGo‡)

3

Free Energy Change (ΔGo)

4

Products

5

B

A or B?

Vmax

1

1/2 Vmax

2

Km

3

C

A, B or C?

Ligands

Cofactors are usually __

The Same Molecule

Isomerases move groups to __

Another Molecule

Transferases move groups to __

Acid/Base Reactions; Redox

What type of reactions are oxidoreductases involved in?

Enzyme

-ase means what?

Conformational Change

The active site undergoes a __ when the substrate and enzyme are close to other another

Yes

Can enzymes change during a reaction?

Weak Acids and Bases

General acid base catalysis uses what?

Acid/Base and Covalent

Chymotrypsin undergoes what type of catalysis?

Stable

Metal ion catalysis works because in order for an enzyme to be effective, the transition state needs to be __. Therefore the metal iron needs to bind to the enzyme to do so.

Protease

Chymotrypsin is a type of __

Smaller Fragments

Proteases chop up proteins into what?

Does Not

A large (high) Km means that the enzyme __ work well on the substrate

Diffusion

E+S →← ES is __ controlled

Faster

A lower Km means the reaction proceeds __

High

Low Km = __ binding affinty

Higher

A high Kcat means the turnover rate is __

Rate-Limiting Step

Kcat is a __

Vmax

Enzymes are limited by the __. (Diffusion)