1. Chapter 6 Enzymes and Feedback Inhibition

2. Enzyme-substrate complex Enzyme Substrate Active site Induced fit

3. The active site of the enzyme can lower an E A barrier by – Orienting substrates correctly – Straining substrate bonds – Providing a favorable microenvironment – Covalently bonding to the substrate © 2014 Pearson Education, Inc.

4. Figure 6.15-1 Substrates Enzyme-substrate complex Substrates are held in active site by weak interactions. Substrates enter active site. 2 1

5. Figure 6.15-2 Substrates Substrates are converted to products. Enzyme-substrate complex Substrates are held in active site by weak interactions. Substrates enter active site. 3 2 1

6. Figure 6.15-3 Substrates Substrates are converted to products. Products are released. Products Enzyme-substrate complex Substrates are held in active site by weak interactions. Substrates enter active site. 4 3 2 1

7. Figure 6.15-4 Substrates Enzyme Substrates are converted to products. Products are released. Products Enzyme-substrate complex Substrates are held in active site by weak interactions. Substrates enter active site. Active site is available for new substrates. 5 4 3 2 1

8. Figure 6.16 Temperature (  C) Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77  C) Optimal temperature for typical human enzyme (37  C) (a) Optimal temperature for two enzymes 120 100 80 60 40 20 0 Rate of reaction Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) (b) Optimal pH for two enzymes pH 9 10 86 4 2 0 7 5 3 1 Rate of reaction

9. Cofactors: Nonprotein enzyme helpers © 2014 Pearson Education, Inc.

10. Figure 6.17 (a) Normal binding Substrate Enzyme Active site (b) Competitive inhibition Competitive inhibitor (c) Noncompetitive inhibition Noncompetitive inhibitor

11. 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. © 2014 Pearson Education, Inc.

13. Active site available Intermediate A End product (isoleucine) Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 Feedback inhibition Isoleucine binds to allosteric site. Isoleucine used up by cell Enzyme 1 (threonine deaminase) Threonine in active site Feedback Inhibition