chapter 6 enzymes and feedback inhibition. enzyme-substrate complex enzyme substrate active site...
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Enzyme-substratecomplex
Enzyme
Substrate
Active site
Induced fit
• The active site of the enzyme can lower an EA barrier by– Orienting substrates correctly– Straining substrate bonds– Providing a favorable microenvironment– Covalently bonding to the substrate
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Figure 6.15-1
SubstratesEnzyme-substratecomplex
Substrates areheld in active site byweak interactions.
Substrates enteractive site.
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Figure 6.15-2
Substrates
Substrates areconverted toproducts.
Enzyme-substratecomplex
Substrates areheld in active site byweak interactions.
Substrates enteractive site.
3
21
Figure 6.15-3
Substrates
Substrates areconverted toproducts.
Products arereleased.
Products
Enzyme-substratecomplex
Substrates areheld in active site byweak interactions.
Substrates enteractive site.
4
3
21
Figure 6.15-4
Substrates
Enzyme
Substrates areconverted toproducts.
Products arereleased.
Products
Enzyme-substratecomplex
Substrates areheld in active site byweak interactions.
Substrates enteractive site.
Activesite is
availablefor new
substrates.
5
4
3
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Figure 6.16
Temperature (C)
Optimal temperature forenzyme of thermophilic
(heat-tolerant) bacteria (77C)
Optimal temperature fortypical human enzyme(37C)
(a) Optimal temperature for two enzymes
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Optimal pH for pepsin(stomach enzyme)
Optimal pH for trypsin(intestinalenzyme)
(b) Optimal pH for two enzymespH
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Cofactors: Nonprotein enzyme helpers
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Figure 6.17
(a) Normal binding
Substrate
Enzyme
Active site
(b) Competitive inhibition
Competitiveinhibitor
(c) Noncompetitive inhibition
Noncompetitiveinhibitor
Concept 6.5: Regulation of enzyme activity helps control metabolism
• Chemical chaos would result if a cell’s metabolic pathways were not tightly regulated.
• A cell does this by switching on or off the genes that encode specific enzymes or by regulating the activity of enzymes.
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Active site available
Intermediate A
End product(isoleucine)
Intermediate B
Intermediate C
Intermediate D
Enzyme 2
Enzyme 3
Enzyme 4
Enzyme 5
Feedbackinhibition
Isoleucinebinds toallostericsite.
Isoleucineused up bycell
Enzyme 1(threoninedeaminase)
Threoninein active site
Feedback Inhibition