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

At which nucleophilic site is serine most likely to be acylated by penicillin in the enzyme-substrate complex?

The carboxyl group of the side chain (–COOH)

The amino group of the backbone (–NH$_2$)

The hydroxyl group of the side chain (–OH) at the $eta$-carbon

The hydrogen atom of the $eta$-carbon

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Verified step by step guidance

Step 1: Understand the context of the problem. Penicillin acts as an irreversible inhibitor by acylating specific nucleophilic sites in enzymes, particularly those involved in bacterial cell wall synthesis. The nucleophilic site must be reactive enough to interact with penicillin's β-lactam ring.

Step 2: Identify the functional groups in serine. Serine contains a hydroxyl group (–OH) on its side chain, a carboxyl group (–COOH), and an amino group (–NH$_2$) in its backbone. Additionally, the hydrogen atom on the β-carbon is present but is not nucleophilic.

Step 3: Evaluate the nucleophilicity of each functional group. The hydroxyl group (–OH) is highly nucleophilic due to the lone pairs of electrons on the oxygen atom, making it a prime candidate for acylation. The carboxyl group (–COOH) and amino group (–NH$_2$) are less likely to be acylated in this context because they are not positioned for direct interaction with penicillin's β-lactam ring.

Step 4: Consider the steric and chemical accessibility of the hydroxyl group. The hydroxyl group on the side chain of serine is located at the β-carbon, making it accessible for interaction with penicillin. This accessibility is crucial for the acylation reaction to occur.

Step 5: Conclude that the hydroxyl group (–OH) at the β-carbon of serine is the most likely nucleophilic site to be acylated by penicillin in the enzyme-substrate complex. This aligns with the mechanism of action of penicillin as an inhibitor.