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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