Question

Which of these statements about enzymes is true? a. Most proteins are enzymes. b. Most enzymes are proteins. c. Enzymes are changed by the reactions they catalyze. d. The active sites of enzymes have little specificity for substrates.

Short answer

The correct statement about enzymes is (b) "Most enzymes are proteins," as the majority of enzymes are proteins, with only a small subset being RNA-based enzymes called ribozymes.

Step-by-step solution

Read and analyze all the statements about enzymes

Read each of the given statements carefully and try to understand what they are claiming about enzymes. a. Most proteins are enzymes. b. Most enzymes are proteins. c. Enzymes are changed by the reactions they catalyze. d. The active sites of enzymes have little specificity for substrates.

Evaluate statement a.

Statement a claims that "most proteins are enzymes." Although enzymes are proteins, not all proteins are enzymes. Proteins have various functions in an organism, and only a subset of proteins acts as enzymes. Therefore, statement a is false.

Evaluate statement b.

Statement b asserts that "most enzymes are proteins." This statement is true, as enzymes are indeed mostly proteins. Although there are some RNA-based enzymes (called ribozymes), the vast majority of enzymes are proteins. Since this statement is true, it's the correct answer.

Evaluate statement c for additional understanding.

Statement c suggests that "enzymes are changed by the reactions they catalyze." This statement is not accurate, as enzymes function as catalysts, speeding up reactions without being consumed or permanently changed in the process. Their structures may temporarily change during the reaction but will return to their original state, ready for another catalytic cycle. Hence, statement c is false.

Evaluate statement d for additional understanding.

Finally, statement d says, "The active sites of enzymes have little specificity for substrates." This statement is incorrect, as enzyme specificity is one of the essential properties of enzymes. The active sites of enzymes are highly specific for their substrates, allowing them to recognize and bind to the correct molecules and catalyze a particular reaction. Therefore, statement d is false.

Conclusion

After analyzing the statements, it is clear that statement (b) "Most enzymes are proteins" is the correct answer, as enzymes are mostly proteins, and this fact is well-established in biochemistry.