Question

Statement 1: Plasmid DNA is circular
Statement 2: Plasmid possess single stranded DNA without polarity

• A. Statement 1 is true and statement 2 is false.
• B. Statement 2 is true and statement 1 is false.
• C. Both statements are false.
• D. Both statements are true.

Hint:

Plasmids are usually circular, double-stranded DNA molecules used as vectors in genetic engineering.

Answer 1

The Correct Option is A

This pair tests two basic facts about plasmid structure, its shape and whether it is single or double stranded.

1. Statement 1, plasmid DNA is circular: A plasmid is a small, self replicating piece of DNA found in bacteria, separate from the main chromosome, and it is almost always closed into a circular loop. This statement is accurate.
2. Statement 2, plasmid possess single stranded DNA without polarity: Plasmids are double stranded, just like the main bacterial chromosome, not single stranded. On top of that, every DNA strand has a direction built into its backbone, running from a 5 prime end to a 3 prime end, so no DNA molecule is ever without polarity. This statement fails on both counts.

Since plasmids really are circular but are double stranded with clear 5 prime to 3 prime polarity, statement 1 is true and statement 2 is false.

Let's summarize:

• Plasmids: small, circular, double stranded, extra chromosomal DNA.
• All DNA, plasmid or otherwise, carries 5 prime to 3 prime polarity, so without polarity is wrong.

So statement 1 is true and statement 2 is false.