Question

There are literally thousands of enzymes at work in complex living systems such as human beings. What properties of the enzymes give rise to their ability to distinguish one substrate from another?

Short answer

In summary, the ability of enzymes to distinguish one substrate from another arises from their unique 3D structure and active site. The 3D structure is determined by the folding patterns of polypeptide chains, which in turn depends on the amino acid sequence. The active site is a pocket-like structure formed by specific amino acid residues, and its shape and chemical properties play a crucial role in determining substrate specificity. The enzyme selectively interacts with a suitable substrate through noncovalent interactions, as explained by the "lock and key" and "induced fit" models. These properties ensure that enzymes maintain proper cellular function in complex living systems by catalyzing specific reactions.

Step-by-step solution

1. Fundamental Understanding of Enzymes

Enzymes are biological molecules that function as catalysts, increasing the rate of chemical reactions occurring in a living organism. They are typically proteins, with some exceptions like ribozymes (RNA molecules with catalytic properties). It is essential to understand the reasons why enzymes can differentiate between substrates, as their specificity is crucial for the proper functioning of various cellular processes.

2. Three-dimensional Structure of Enzymes

One of the crucial properties that allow enzymes to distinguish between different substrates is their unique 3D structure. The 3D structure is determined by folding patterns of the polypeptide chains of the enzymes. This structure, in turn, is dependent on the amino acid sequence, which is encoded in the genes. Due to variations in primary structure (amino acid sequence), enzymes have diverse folding patterns leading to different 3D structures, eventually influencing their substrate specificity.

3. Active Site of the Enzyme

The region where substrates bind to the enzyme and undergo catalysis is known as the active site. Active sites are typically formed by specific amino acid residues that create a unique pocket or groove-like structure. The shape and chemical properties of the active site play a crucial role in determining the substrate specificity of enzymes.

4. Active Site-Substrate Interaction

The active site specifically interacts with the substrate through noncovalent interactions, such as hydrogen bonding, ionic interactions, and hydrophobic contacts. An essential concept in enzyme specificity is the "lock and key" model, which proposes that the enzyme's active site (lock) matches the substrate's shape and chemical properties (key). Another model called the "induced fit" theory suggests that the enzyme and substrate undergo conformational changes upon interaction for better complementarity. Both models emphasize the enzyme's selective interaction with a suitable substrate.

Conclusion

In summary, the properties that give rise to enzymes' ability to distinguish one substrate from another are the 3D structure and active site. The unique folding pattern of an enzyme results in an active site that selectively binds to the substrate with a specific shape and chemical properties. This specificity ensures that enzymes catalyze specific reactions in complex living systems, maintaining proper cellular function.