Why do enzymes only work on their specific substrates?

• A. Because the active site of an enzyme has a unique shape that fits only its specific substrate, following the 'lock and key' model.
• B. Because enzymes randomly bind to any molecule present in the cell.
• C. Because enzymes require high temperatures to function, which only certain substrates can withstand.
• D. Because enzymes are consumed during the reaction and can only be used once.

Answer: (A)

Verified step by step guidance

1. Understand the role of enzymes: Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to occur. They are highly specific to the reactions they catalyze.
2. Learn about the 'lock and key' model: This model explains enzyme specificity. The active site of an enzyme has a unique three-dimensional shape that matches the shape of its specific substrate, similar to how a key fits into a specific lock.
3. Recognize the importance of the active site: The active site is the region of the enzyme where the substrate binds. The specific shape and chemical properties of the active site ensure that only the correct substrate can bind effectively.
4. Eliminate incorrect options: Enzymes do not randomly bind to any molecule; their specificity is due to the precise fit of the substrate in the active site. Enzymes are not consumed during the reaction—they are reusable. Additionally, enzymes do not require high temperatures to function; they work under physiological conditions.
5. Conclude with the correct explanation: Enzymes only work on their specific substrates because the active site of the enzyme has a unique shape that fits only its specific substrate, following the 'lock and key' model.