Question

Which of the following are the properties of a good cloning vector
(A). Ideally should be less than 10 kb
(B). Isolation and purification should be easy
(C). Should contain a unique target site
(D). Able to replicate autonomously
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A), (B) and (C) only.
• C. (A), (C) and (D) only.
• D. (B), (C) and (D) only.

Hint:

When evaluating properties of a biological tool like a vector, distinguish between fundamental requirements (like replication and insertion sites) and desirable features for convenience (like small size or high copy number). The fundamental requirements are always the most important.

Answer 1

The Correct Option is D

Step 1: Cloning Vector Basics:
A cloning vector is a small DNA segment that can stably exist within an organism and accept a foreign DNA fragment for cloning. Key features are essential for a cloning vector to be effective in molecular biology.
Step 2: Property Breakdown:
Let's examine each property:
(A) Size: ideally less than 10 kb: Smaller plasmid vectors are easier to handle, manipulate, and transform efficiently. However, this isn't universal. For large DNA fragments, larger vectors like Bacterial Artificial Chromosomes (BACs, 100-300 kb) or Yeast Artificial Chromosomes (YACs, >300 kb) are used. Thus, this is helpful, but not always required.
(B) Easy Isolation: This is crucial. A vector must be easily separated from the host cell's DNA in high quantity and purity.
(C) Unique Target Site: This is essential. Vectors need at least one, and preferably many, unique restriction enzyme recognition sites, usually in a Multiple Cloning Site (MCS). This ensures the enzyme cuts the vector in only one place, allowing insertion of the foreign DNA.
(D) Autonomous Replication: This is a defining trait. Vectors must have an origin of replication (ori) that lets the host cell's machinery replicate it independently of the host's chromosome. This ensures the vector and inserted DNA are copied and passed on to daughter cells.
Step 3: Conclusion:
Properties (B), (C), and (D) are fundamental to nearly all cloning vectors. Property (A) is helpful for efficiency, especially for plasmids, but is not a defining characteristic for all vector types. Thus, the most accurate combination of essential properties is (B), (C), and (D).