Question

A suitable cloning vector must have following features
A. Multiple cloning site
B. Unique restriction site for several restriction enzymes
C. One or few selectable markers
D. Very large size
E. An origin or replication
Choose the correct answer from the options given below:

• A. A, B, C, D and E
• B. A, B, C and E only
• C. A, C, D and E only
• D. B, C, D and E

Hint:

Cloning Vector Requirements:
1. Ori (The Motor)
2. Marker (The Filter)
3. MCS (The Door)
4. Small Size (The Portability)
If a vector is too big, it becomes a "Unstable Giant" in the cell!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to evaluate the essential structural requirements for an ideal DNA molecule (vector) used to carry and replicate foreign DNA in a host cell.

Step 2: Detailed Explanation:

• Origin of Replication (E): This is the most critical feature. It allows the vector to replicate independently within the host cell (autonomy).

• Selectable Markers (C): These are genes (like antibiotic resistance) that allow scientists to distinguish between cells that have taken up the vector and those that have not.

• MCS and Unique Sites (A & B): A Multiple Cloning Site (MCS or Polylinker) is a short region containing many unique restriction sites. "Unique" means the enzyme cuts only at that one spot in the entire vector, ensuring the foreign DNA is inserted precisely without chopping the vector into pieces.

• The Size Factor (D): Unlike the statement suggests, a small size is generally preferred for a cloning vector. Large plasmids are difficult to handle, tend to break during purification, and are very inefficient at transforming host cells. Small vectors also have a lower risk of containing unwanted extra restriction sites.

Step 3: Final Answer:
An ideal cloning vector requires an Ori, selectable markers, and a polylinker with unique sites, but it should be small rather than "very large" for stability and ease of use.