Control METABOLISM Metabolic reactions can be

controlled and sped up by enzymes metabolic reactions would be

too slow to occur if no enzymes were present!

End in “ase”

Properties of Enzymes1.Proteins2.Catalysts3.Reusable 4.Substrate

specific5.Sensitive to

temperature6.Sensitive to

pH

Enzymes Remain Unchanged! Enzymes are not

used up; Reaction ends when there is NO MORE SUBSTRATE!!

Synthesis or Decomposition reactions

substrate

enzyme

active site

substrate

Mechanism of Enzyme ActionMechanism of Enzyme Action• Each enzyme has an ACTIVE SITE!!• Active site is the place where the

substrate binds with the enzyme

enzyme

Action of Enzyme in Action of Enzyme in SynthesisSynthesis

substrate

substrate

enzyme-substrate complex

Product and

enzyme

Action of Enzyme in Action of Enzyme in DecompositionDecomposition

substrate

enzyme-substrate complex

product

Lock and Key Hypothesis

Enzyme

Substrate

Lock and Key Hypothesis

SHAPES

DON’T

MATCH

Lock & Key Model ONE enzyme for every substrate

Unique fit

Enzyme

Substrate

Enzymes are Temperature Dependent…...

Most work BEST at body temperature

37oC DENATURE at high

temperatures

Inactive at LOW temperature

Effect of pH on Enzyme Activity

Optimum pH : the pH value at which the enzyme has the highest activity (fastest rate of reaction)

--Different enzymes may have different optimum pH’sDifferent enzymes may have different optimum pH’s

-If pH is higher or lower than optimum pH, -If pH is higher or lower than optimum pH, denaturation happens; enzyme becomes ineffective.denaturation happens; enzyme becomes ineffective.

What pH does pepsin work best?

What pH does pancreatic lipase work?

Enzyme Lab Enzyme: catalase Source: liver, potato,

apple etc Substate:H2O2(Hydrogen

Peroxide)

Hydrogen peroxide is toxic in cells

2H2O2 +catalase 2 H2O + O2