Enzymes

Characteristics

• All Enzymes are Proteins• Catalysts – i.e. control the rate of a

chemical reaction

How Enzymes work

• Enzymes bind and hold substrates (aka reactants) in a certain orientation to speed the chemical reaction along

• Enzymes change shape as they bind the substrates

the binding

+

substrates

active site enzyme-substrate complex

the reaction, the release

enzyme-substrate complex

product

What about the other way?

enzyme-substrate complexsubstrate

enzyme

product

Lactase

• 1926 aa’s long• cell membranes - small intestines

Lactase

Beano - alpha galactosidase

• breaks down trisaccharides•raffinose – in beans, cabbage

• enzyme • not in humans• in bacteria in large intestines

+

another example – glyceraldehyde-3-dehydrogenase

re-introducing activation energy

net energy change

acti

vati

on

en

erg

y

–activation energy is the energy required to get a reaction going

How do Enzymes work?• They lower the “activation energy” of the reaction

net energy change

–activation energy is the energy required to get a reaction going

activation energy

How do they do it?• They lower the “activation energy” of the reaction

net energy change

Enzyme performance is affected by:

– amount of substrate present– temperature– pH– Inhibitors– Poisons

Enzymes and Amount of Reactants [ reactants ] reaction rate

because increased chance of finding molecules

[reactants] reaction rate because decreased chance of finding molecules

Experiment with amount and rate

1. Measure [S] or [P] 2. Combine and Plot

Enzymes and Temperature

temperature reaction rate because increased kinetic energy breaks H-bonds

temperature reaction rate because decreased kinetic energy does not break H-bonds

pH

• Acids – excess Hydrogen ions• Bases – excess hydroxyl ions• Neutral – equal numbers of H+

and OH-

Enzymes and pH

pH changes reaction rate becauseH-bonds are altered

pH changes reaction rate because H-bonds are altered

Experiment with pH and rate

Enzymes and pH each enzyme has an optimal pH; some work best in acidic conditions (<4) (pepsin) while others work best closer to a neutral pH (7)

pH for Optimum Activity Enzyme pH Optimum

Lipase (pancreas) 8.0Lipase (stomach) 4.0 - 5.0Lipase (castor oil) 4.7Pepsin 1.5 - 1.6Trypsin 7.8 - 8.7Urease 7.0Invertase 4.5Maltase 6.1 - 6.8Amylase (pancreas) 6.7 - 7.0Amylase (malt) 4.6 - 5.2Catalase 7.0

Enzymes and Inhibitors

Enzymes and Inhibitors bind to specific enzymes and decrease the reaction rate

Normal substrate enzyme binding

Competitive inhibitor binds to the active site

Noncompetitive inhibitor binds to the enzyme and changes its shape

Competitive Inhibitors

Noncompetitive Inhibitors

Poisons - KCN

• Specific Irreversible Inhibitor of Cytochrome C Oxidase,

• ATP cannot be made

• Anaerobic respiration only

• Fatal build up - Lactic Acid

Poisons - Arsenic• Nonspecific Inhibitor of cellular respiration enzymes

• Inhibits glucose break down

• Cell death results