Identify the statement which is not true for restriction enzymes ?

Options

A. Some 900 restriction enzymes have been isolated till date
B. They cut each of the two strands of DNA at spe- cific points through their sugar phosphate back- bone
C. The naming of restriction enzymes follows the se- quence strain name follow ed by species name fol- lowed by genus name
D. The restriction enzymes can be both exonucleases as well as endonucleases

Answer

To identify the statement that is not true for restriction enzymes, we will analyze each statement provided in the question step by step.

### Step 1: Analyze the first statement
The first statement claims that "some 900 restriction enzymes have been isolated till date."
- This statement is **true**. In reality, over 900 restriction enzymes have been identified from various strains of bacteria.

### Step 2: Analyze the second statement
The second statement states that "they cut each at the two strands of DNA at specific points through their sugar phosphate backbone."
- This statement is also **true**. Restriction enzymes cut the DNA at specific sites, which are usually palindromic sequences, breaking the sugar-phosphate backbone.

### Step 3: Analyze the third statement
The third statement mentions that "the naming of restriction enzymes follows the sequence strain name followed by species name followed by genus name."
- This statement is **false**. The correct naming convention for restriction enzymes is that the first letter comes from the genus name, the next two letters come from the species name, followed by a letter indicating the strain, and then a Roman numeral indicating the order of discovery.

### Step 4: Analyze the fourth statement
The fourth statement asserts that "the restriction enzymes can be both exonuclease as well as endonuclease."
- This statement is **true**. Restriction enzymes can function as both exonucleases (which cut at the ends of DNA) and endonucleases (which cut within the DNA strand).

### Conclusion
After analyzing all the statements, we find that the **third statement** is the one that is not true regarding restriction enzymes.

### Final Answer
The statement which is not true for restriction enzymes is: "The naming of restriction enzymes follows the sequence strain name followed by species name followed by genus name."

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