Table of contents

1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

6. Enzymes and Enzyme Kinetics

Enzyme-Substrate Complex

Biochemistry

6. Enzymes and Enzyme Kinetics

Enzyme-Substrate Complex

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Multiple Choice

For what mechanistic reason does Glu-1 (G1) of lactase first act as a Brønsted acid during catalysis?

To form a covalent intermediate with the substrate.

To coordinate a metal ion required for catalysis.

To stabilize the transition state by accepting a proton from the substrate.

To donate a proton to the glycosidic oxygen, facilitating cleavage of the glycosidic bond.

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Verified step by step guidance

Step 1: Understand the role of Glu-1 (G1) in the lactase enzyme. Glu-1 is a glutamate residue, which has a carboxylic acid functional group capable of donating a proton (acting as a Brønsted acid). This property is essential for its catalytic function.

Step 2: Recall the mechanism of glycosidic bond cleavage. Glycosidic bonds connect sugar molecules, and their cleavage often requires protonation of the glycosidic oxygen to destabilize the bond and facilitate its breakdown.

Step 3: Analyze the options provided. The correct mechanistic reason involves Glu-1 donating a proton to the glycosidic oxygen, which weakens the bond and allows for cleavage. This aligns with the role of Glu-1 as a Brønsted acid.

Step 4: Eliminate incorrect options. For example, forming a covalent intermediate or coordinating a metal ion are not relevant to the specific role of Glu-1 in this reaction. Similarly, stabilizing the transition state by accepting a proton does not describe the proton donation process.

Step 5: Conclude that the correct answer is: 'To donate a proton to the glycosidic oxygen, facilitating cleavage of the glycosidic bond.' This step highlights the importance of proton donation in enzymatic catalysis and the specific function of Glu-1 in lactase.