Which of the following statements about supercoiling of DNA are true?
(1) Supercoiled DNA differs in linking number from relaxed DNA.
(2) Supercoiled DNA can be relaxed through the action of topoisomerases.
(3) All DNA in the cell is positively supercoiled.
(4) A negatively supercoiled DNA is more difficult to unwind.
A) Only 2, 3 and 4 are true
B) Only 1, 2 and 3 are true
C) Only 1 and 3 are true
D) Only 1 and 2 are true
E) All are true

Question

Quizplus · Accepted Answer

(1) Supercoiled DNA differs in linking number from relaxed DNA. This is true. Supercoiled DNA has a different linking number than relaxed DNA due to the winding and twisting that occurs.
(2) Supercoiled DNA can be relaxed through the action of topoisomerases. This is true. Topoisomerases are enzymes that can break, swivel, and rejoin DNA strands, allowing for the relaxation of supercoiled DNA.
(3) All DNA in the cell is positively supercoiled. This statement is false. Some DNA can be positively supercoiled, while other DNA can be negatively supercoiled or relaxed.
(4) A negatively supercoiled DNA is more difficult to unwind. This statement is true. Negatively supercoiled DNA has a higher torsional strain and is therefore more difficult to unwind than positively supercoiled or relaxed DNA.

Which of the Following Statements About Supercoiling of DNA Are