Which of these is false about enzymes?

Options

A. Nucleic acid which behave as enzymes are called ribozymes
B. Enzymes only catalyse the reaction and do not initiate it.
C. All enzymes are subjected to degradation at a temperature of more than `40^@C`
D. A reaction producing 200 molecules of `H_2CO_3` increases to 600,000 molecule in the presence of carbonic anhydrase.

Answer

To determine which statement about enzymes is false, we will analyze each option provided in the question step by step.

### Step 1: Understand what enzymes are
Enzymes are biological catalysts that speed up chemical reactions without being consumed in the process. They are typically proteins, but some RNA molecules can also act as enzymes (these are called ribozymes).

**Hint:** Remember that enzymes facilitate reactions and are not permanently altered by the reactions they catalyze.

### Step 2: Analyze Option 1
Option 1 states: "Nucleic acids which behave as enzymes are called riboenzymes."
- This statement is true. Riboenzymes are RNA molecules that have catalytic activity, meaning they can catalyze biochemical reactions.

**Hint:** Consider the role of RNA in catalysis and its distinction from proteins.

### Step 3: Analyze Option 2
Option 2 states: "Enzymes not only catalyze the reaction but do not initiate it."
- This statement is somewhat misleading. While enzymes do catalyze reactions, they can also lower the activation energy required for a reaction to occur, effectively allowing the reaction to proceed. However, they do not initiate reactions independently; they require substrates to act upon.

**Hint:** Think about the role of enzymes in lowering activation energy and how they interact with substrates.

### Step 4: Analyze Option 3
Option 3 states: "All enzymes are subject to degradation at a temperature of more than 40°C."
- This statement is false. While many enzymes denature (lose their functional shape) at high temperatures, not all enzymes degrade at 40°C. Some enzymes are adapted to function at higher temperatures, such as those found in thermophilic organisms.

**Hint:** Consider the diversity of enzymes and their temperature stability.

### Step 5: Analyze Option 4
Option 4 states: "A reaction producing 200 molecules of H2CO3 increases to 6 lakh molecules in the presence of carbonic anhydrase."
- This statement is true. Carbonic anhydrase is an enzyme that catalyzes the conversion of carbon dioxide and water to carbonic acid, significantly increasing the amount of H2CO3 produced.

**Hint:** Recall the specific function of carbonic anhydrase in biochemical reactions.

### Conclusion
After analyzing all the options, we conclude that **Option 3** is the false statement about enzymes. It incorrectly claims that all enzymes degrade at temperatures above 40°C.

**Final Answer:** Option 3 is false.