Enzymes

Front 1

Classes of enzymes

Back 1

oxidoreductases

transferases

hydrolases

lysases

isomerases

ligases

Front 2

Enzyme activity and temperature

Back 2

- at low temperatures rate increase with temperature b/c increased kinetic activity and substrate molecules

-further temp increase results in enzyme denaturation and loss of enzyme activity

Front 3

Optimal Temperature

Back 3

The temperature range over which an enzyme denatures varies among enzymes and organisms

rxn rate of human enzymes is max at 37 C normal body temperature

enzymes of homeotherms are inactivated by temps above 50-55 C

Front 4

Ranges of heat sensitivity

Back 4

some enzymes will denature at temps < 40 C

some retain activity at high temps eg. Archeae

Cryophilic (cold loving) function at low temperatures such as Listeria bacteria

Front 5

Sensitivity to pH

Back 5

enzymes active in pH of 3-4 units

pH change affects the charge of residues and can disrupt ionic and hydrogen bonds

pH dependence- due to presence of charged amino acids at active site or on substrate

Front 6

Sensitivity to other factors

Back 6

sensitive to molecules and ions that act as inhibitors or activators

ionic strength of environment

this affects hydrogen bonding and ionic interactions needed to maintain tertiary conformation

Front 7

Why does the substrate binding, activation, and catalysis occur at active site

Back 7

the precise chemical fit between the active site of the enzyme and its substrate, enzymes are highly specific

Front 8

Substrate binding

Back 8

involves hydrogen bonds, ionic bonds, or both

is readily reversible

Front 9

Induced fit model

Back 9

substrate binding at the active site induces a conformational change in the shape of the enzyme

Front 10

conformational change

Back 10

brings needed amino acid side chains into the active site

sometimes not nearby if substrate is bound to the active site

Front 11

Substrate activation

Back 11

to recognize and bind the best fit substrate and activate it by providing the right catalysis

Front 12

Mechanism of substrate activation

Back 12

bond distortion- making it more susceptible to catalytic attack

proton transfer- increases reactivity of substrate

electron transfer- resulting in temporary covalent bonds between enzyme substrate

Front 13

The catalytic event

Back 13

1. random collision of a substrate molecule w/ active site results in it binding there

2. substrate binding induces a conformational change that tightens the fit, facilitation the conversion of substrate into products

3. products then released from active site

4. enzyme molecule returns

Front 14

enzyme kinetics

Back 14

describes quantitative aspects of enzymes catalysts and rate of substrate conversion into products

rxn rates influenced by factors such as concentrations and substrates, products and inhibitors

Front 15

initial rxn rates

Back 15

measured over a brief time which the substrate concentration has not yet decreased enough to affect the rate of rxn

Front 16

Michaelis- menten kinetics

Back 16

intitial rxn velocity (v) - the rate change in product concentration per unit time depends on substrate concentration (S)

At low S doubling S will double v

As S increases each increase = smaller increase in v

when S is large v reaches maximum

Front 17

V max and saturation

Back 17

As S moves toward infinity v approaches an upper limiting value (maximum velocity)

Vmax can be increased by adding more enzyme

inability of increasingly higher substrate conc. to increase the rxn velocity beyond finite upper value (saturation)

Front 18

Michaelis- menton equation

Back 18

S----P-----ES----E + P