Enzymes

Enzymes are…

• Proteins that act as catalysts (accelerate reactions) by creating a new reaction pathway

• Are specific for what they catalyze and do not permanently change during reactions

• End in the word -ase

Function of Enzymes• Enzymes work by lowering the activation

energy (the amount of energy needed to start a reaction).

Check for Understanding

With your partner, label the products, reactants, activation energy, progress of reaction, and free energy on the image below. Question: Using this image, what is one thing that the enzyme does in this reaction?

Enzyme-Substrate Complex

• Substrate is the substance an enzyme acts on and is specific for each enzyme

• Active site is the region of the enzyme that binds to the substrate

EnzymeSubstrate

Active Site

Lock-and-Keys Model

Enzyme may be used again

Enzyme-substrate complex

E

S

P

E

E

P

Reaction coordinate

Lock-and-Keys Model

• Keys = Substrates (multiple can bind to each enzyme)

• Lock = Active Site on the Enzyme• As a result of the reaction, the products

change shape• After the reaction is complete, the substrates

are released, freeing up the enzymes to bind with more substrate

Check for Understanding

With your partner, using what we just discussed, fill in the boxes on the diagram below. Include the name of the part of the enzyme or substrate, and the events that are taking place for the boxes labeled #1-4.

Active Site

Enzyme

Substrate matching the enzyme approaches the active site

The substrate bonds to the active site forming the enzyme-substrate complex

Product Product

The products formed are released and the enzyme is free to bind to a new substrate

The enzyme speeds up the reaction, changing the shape of the substrate

Induced Fit

10

• A change in the configuration of an enzyme’s active site (H+ and ionic bonds are involved).

• Induced by the substrate.

Enzyme

Active Sitesubstrate

induced fit

Factors that Impact Enzyme Function

• Temperature• pH• Substrate Concentration • Inhibitors

Temperature

• Enzymes move faster as temperature increases

• Above optimum temperature, the enzyme denatures – preventing it from binding with the substrate

Temperature / °C

Enzyme activity

0 10

20

30

40

50

Denaturation

pH

• Extreme pH will result in denaturation

• Enzyme structure changes

• Substrate will no longer fit

• pH levels different for different enzymes

Optimum pH values

Enzyme activity Trypsin

Pepsin

pH1 3 5 7 9 11

Substrate Concentration

• More substrate causes the substrate to use up the available enzyme faster

• Once all of the enzyme is bound, the reaction will slow and move at a constant state

Competitive Inhibitors

• Chemicals that resemble an enzyme’s normal substrate and compete with it for the active site

EnzymeSubstrate

Noncompetitive Inhibitors

• Chemicals that bind to part of the enzyme (not the active site), resulting in changing the shape of the active site prevents the substrate from binding

Enzymeactive site altered

NoncompetitiveInhibitor

Substrate