DNA Supercoiling

Since the amount of DNA contained by a cell is often much longer than the cell itself, the genetic material must be packaged such that it can fit into a compact space. The process of supercoiling allows very long DNA molecules to be contained within the relatively small area of a cell by twisting the double helix into a more tightly coiled and compact structure. Enzymes called gyrases are responsible for compressing DNA in this way and wind the double helix about its own axis much like a twisted rubber band, as shown in this animation. In some cases, DNA supercoils may wrap around proteins such as histones, which are then said to be constricted. Alternatively, supercoiling can occur as displayed here, when no protein is constrained by the DNA.

Question 1: How does DNA gyrase allow DNA molecules to be wound into a tightly coiled and compact structure?
  1. Ligation
  2. Replication
  3. Recombination
  4. Supercoiling

Answer 1

Answer (d) - Supercoiling

Question 2: DNA may wrap around ________ to form supercoils.
  1. histones
  2. ribosomes
  3. proteomes
  4. chromosomes

Answer 2

Answer (a) - histones