how enzymes function
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HOW ENZYMES FUNCTION. 5.14 Activation Energy. Activation energy ( E A ): Energy available to break bonds and form new ones Although there is a lot of potential energy in biological molecules, such as carbohydrates, it is not released spontaneously. Reaction without enzyme. E A without - PowerPoint PPT PresentationTRANSCRIPT
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HOW ENZYMES FUNCTION
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5.14 Activation Energy
• Activation energy (EA): Energy available to break bonds and form new ones
• Although there is a lot of potential energy in biological molecules, such as carbohydrates, it is not released spontaneously
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Reactionwithoutenzyme
EA with enzyme
Ener
gy Reactants
Reaction withenzyme
EA withoutenzyme
Netchangein energy(the same)
ProductsProgress of the reaction
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• Purpose: to lower the Energy of Activation Ea
• Enzymes are proteins and specific in shape
• If shape changes the enzyme will not function b/c substrate is specific for active site
5.14 Enzymes- Purpose
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5.15 Enzymes- Specific Structure
• Enzymes have unique three-dimensional shapes
– As a result of its shape, the enzyme has an active site where the enzyme interacts with the enzyme’s substrate
– Consequently, the substrate’s chemistry is altered to form the product of the enzyme reaction
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Substrate
Active site
Enzyme Enzyme-substratecomplex
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Enzyme availablewith empty activesite
Active site
1
Enzyme(sucrase)
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Enzyme availablewith empty activesite
Active site
1
Enzyme(sucrase)
Substrate bindsto enzyme withinduced fit
2
Substrate(sucrose)
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Enzyme availablewith empty activesite
Active site
1
Enzyme(sucrase)
Substrate bindsto enzyme withinduced fit
2
Substrate(sucrose)
Substrate isconverted toproducts
3
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Enzyme availablewith empty activesite
Active site
1
Enzyme(sucrase)
Substrate bindsto enzyme withinduced fit
2
Substrate(sucrose)
Substrate isconverted toproducts
3Products arereleased
4
Fructose
Glucose
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5.15 Enzymes- Environmental Conditions
• Enzymes require certain environmental conditions
– Temperature is very important– human enzymes function best at 37ºC, or body temperature– High temperature will denature (change the shape of)
human enzymes
– Enzymes also require a pH – around neutral for best results
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5.15 Enzymes- Environmental Conditions
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5.15 Enzymes- Cofactors
• Some enzymes require non-protein helpers
– Cofactors are inorganic, such as zinc, iron, or copper
– Coenzymes are organic molecules and are often vitamins
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5.16 Enzymes- Inhibitors
• Competitive inhibitors bind to the active site of an enzyme, competing with the substrate
• Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective
• Examples of inhibitors include toxins, poisons, pesticides, and antibiotics
• BOTH type inhibit enzyme activity!
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Substrate
Enzyme
Active site
Normal binding of substrate
Competitiveinhibitor
Enzyme inhibition
Noncompetitiveinhibitor
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5.16 Enzyme Inhibitors
• Is inhibition reversible?
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Covalent bonds form between Enzyme and Inhibitor!
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5.16 Enzyme Inhibitors
• Enzyme inhibitors are important in regulating cell metabolism
• Feedback inhibition: when the product of a reaction can serve as an inhibitor of one enzyme in the same reaction
– The more product formed, the greater the inhibition = regulation of the reaction
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5.16 Enzyme Inhibitors
• What would happen if they did not produce feedback inhibitors??
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5.16 Enzyme Inhibitors
• There would be chaos in the cell!
• Too many chemical reactions!