Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

21. Aldehydes and Ketones: Nucleophilic Addition

Nucleophilic Addition

Organic Chemistry

21. Aldehydes and Ketones: Nucleophilic Addition

Nucleophilic Addition

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Problem 39

Textbook Question

Carbonic anhydrase is an enzyme that catalyzes the conversion of carbon dioxide to bicarbonate ion. It is a metalloenzyme, with Zn²⁺ coordinated at the active site by three histidine side chains. Propose a mechanism for the reaction.

Verified step by step guidance

Step 1: Recognize that carbonic anhydrase is a metalloenzyme with Zn²⁺ at its active site. The Zn²⁺ ion is coordinated by three histidine residues, which stabilize the enzyme's active site and facilitate the reaction.

Step 2: Understand the role of Zn²⁺ in activating water (H₂O). The Zn²⁺ polarizes the water molecule, making it more acidic and facilitating the loss of a proton (H⁺) to generate a hydroxide ion (OH⁻). This hydroxide ion is a strong nucleophile.

Step 3: The hydroxide ion attacks the carbon dioxide (CO₂) molecule, which is electrophilic due to the partial positive charge on the carbon atom. This nucleophilic attack forms a transient intermediate, likely a zinc-bound bicarbonate species.

Step 4: The intermediate rearranges to release the bicarbonate ion (HCO₃⁻) from the active site. The Zn²⁺ remains coordinated with water, ready to repeat the catalytic cycle.

Step 5: The proton (H⁺) released during the activation of water is transferred to the surrounding environment, completing the reaction and maintaining charge balance.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enzyme Catalysis

Enzyme catalysis refers to the process by which enzymes accelerate chemical reactions. Enzymes lower the activation energy required for a reaction to occur, allowing it to proceed more quickly and efficiently. In the case of carbonic anhydrase, it facilitates the conversion of carbon dioxide and water into bicarbonate and hydrogen ions, demonstrating how enzymes can enhance reaction rates in biological systems.

Metalloenzymes

Metalloenzymes are enzymes that contain metal ions as essential components for their activity. These metal ions, such as zinc in carbonic anhydrase, play crucial roles in stabilizing enzyme structure and participating in the catalytic process. The coordination of zinc with histidine side chains at the active site is vital for the enzyme's function, influencing substrate binding and the overall reaction mechanism.

Acid-Base Chemistry

Acid-base chemistry involves the transfer of protons (H+) between molecules, which is fundamental to many biochemical reactions. In the reaction catalyzed by carbonic anhydrase, water acts as a base, accepting a proton to form hydroxide, while carbon dioxide is converted into bicarbonate. Understanding the acid-base dynamics is essential for grasping how the enzyme facilitates the conversion and maintains pH balance in biological systems.

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