If each of the following amino acid side chains is present in the active site of an enzyme, indicate whether it would (a) serve a catalytic function, (b) serve to hold the substrate, or (c) both.
a. aspartate

Verified step by step guidance

1. Understand the problem: The question asks us to determine the role of the amino acid side chain (aspartate) in the active site of an enzyme. The options are (a) catalytic function, (b) holding the substrate, or (c) both.
2. Recall the structure and properties of aspartate: Aspartate is a negatively charged amino acid at physiological pH due to its carboxylate (-COO⁻) group in the side chain. This charge makes it capable of interacting with positively charged groups or participating in acid-base catalysis.
3. Consider catalytic function: Aspartate can serve a catalytic function because its negatively charged side chain can act as a nucleophile or participate in proton transfer during enzymatic reactions.
4. Consider substrate binding: The negative charge on aspartate's side chain can also interact with positively charged regions of the substrate, helping to hold the substrate in place within the active site.
5. Conclude the role: Based on its ability to participate in both catalytic activity and substrate binding, aspartate can serve both functions (c).

Key Concepts

Amino Acid Side Chains

Amino acid side chains, or R groups, determine the chemical properties and functions of amino acids in proteins. They can be polar, nonpolar, acidic, or basic, influencing how they interact with substrates and other molecules. Understanding the nature of these side chains is crucial for predicting their roles in enzyme activity, including catalysis and substrate binding.

Enzyme Active Site

The active site of an enzyme is a specific region where substrate molecules bind and undergo a chemical reaction. The structure and chemical environment of the active site are tailored to facilitate the conversion of substrates into products. The presence of specific amino acid side chains in this region can enhance catalytic efficiency or stabilize substrate binding.

Catalytic Function vs. Substrate Binding

Catalytic function refers to the ability of an enzyme to accelerate a chemical reaction, often involving the formation of transient intermediates. In contrast, substrate binding involves the non-covalent interactions that hold the substrate in place within the active site. Some amino acids can perform both roles, while others may specialize in one, impacting the overall enzymatic activity.