Chapter 8 - Enzyme Kinetics

What does a catalyst do?

speeds up reaction, lowers activation energy

What are the six classes of enzymes?

oxidoreductase, transferase, hydrolase, lyase, isomerase, ligase

What is inhibition?

When a molecule other than the substrates binds to and inactivates the enzyme

What is a regulatory protein?

Reversibly bind to the enzyme to inhibit activity

Define covalent modification

The enzyme may be synthesized in an inactive form (a zymogen) and activated when needed

True/false. Enzymes alter equilibria

False

Equation for Gibbs Free Energy

ΔG = ΔH - TΔS

equation for Gibbs free energy in relation to equilibrium

ΔG = ΔG° + RT ln([products]/[reactants]) = ΔG° + RT ln Keq

When is a reaction spontaneous?

When ΔG is negative

free energy and equilibrium constant

∆G = ∆G° + RTlnQ

At equilibrium ∆G = 0

0 = ∆G° + RTlnKeq

∆G° = - RTlnKeq

Keq= e^-ΔG°/RT (kJ)

Conversion of kJ to kcal is 4.184kJ=1kcal

General reaction of enzyme:substrate complex

E + S

What is the active site?

The active site is the region on the enzyme where the substrate binds, it is a small pocket or crevice

lock and key mechanism

A model suggesting that the shape of a substrate molecules is an exact fit to the shape of an enzyme's active site

induced fit mechanism

binding of substrate to enzyme causes a small shape change that reduces energy of activation

Michaelis-Menten equation

v = (vmax [S])/(Km + [S])

What is Km (Michaelis constant)?

(K-1+K2)/ K1

What happens in the Michaelis Menton plot when [S] is small?

V= S So V is directly proportional to [S] when [S] is low

What happens when [S] is high?

V=Vmax

What happens when [S] = Km

Vo = Vmax/2 The rate is 1/2 the max value

line weaver burk equation

1/V = (Km/Vmax)(1/[S]) + 1/Vmax y=mx+b

What is the x-intercept of the Lineweaver-Burk plot?

-1/Km

What is the y-intercept of the Lineweaver-Burk plot?

1/Vmax

What is the turnover number?

number of substrate molecules an enzyme converts to a product when the enzyme is saturated.

Kcat=K2

Rate of reaction using turnover number

V0 = (Kcat/Km)[E]total[S]

What is competitive inhibition?

An inhibitor competes with the substrate for binding to the active site.

How can we identify competitive inhibition on the line weaver burk plot?

The lines will cross at the Y intercept… the competitive line is higher

Competitive inhibition equation

1/V = 1/Vmax + (1 + [I]/Ki)(1/[S])

What is noncompetitive inhibition?

The inhibitor binds to a site on the enzyme, not the active site, and changes the conformation of the enzyme so that it is no longer active

How can we identify non competitive inhibition on a graph?

It intersects at the X-intercept

Noncompetitive inhibition equation

1/V = 1/Vmax + (Km/Vmax)(1 + [I]/Ki)(1/[S])

What is uncompetitive inhibition?

binds only to the enzyme-substrate complex, essentially locking the substrate in the enzyme, preventing its release

Uncompetitive inhibition equation

1/V = 1/Vmax (1 + [I]/Ki)+(1/[S]) (Km/Vmax)

How can we identify uncompetitive inhibition on a graph?

The lines will be parallel

What is irreversible inhibition?

Irreversible inhibition refers to the prolonged or permanent inactivation of an enzyme, such that it cannot be easily renatured to gain function.