Supercoiling

Definition

Supercoiling is the over-winding or under-winding of a DNA strand, and is an expression of the strain on that strand. It helps compact DNA to fit within cellular structures and plays a role in regulating gene expression.

5 Must Know Facts For Your Next Test

1. Supercoiling occurs when the DNA helix twists on itself due to enzymatic activities such as those by topoisomerases.
2. Positive supercoiling overwinds the DNA, making it tighter, whereas negative supercoiling underwinds it, making it looser.
3. Topoisomerases are enzymes that manage DNA supercoiling by cutting and rejoining DNA strands.
4. Supercoiled DNA can be more easily packed into the limited space of a cell nucleus or bacterial nucleoid.
5. The degree of supercoiling can affect processes like transcription and replication by influencing the accessibility of DNA to various enzymes.

Review Questions

• What are the two types of supercoiling and how do they differ?
• Which enzyme is primarily responsible for altering the supercoiled state of DNA?
• How does supercoiling affect gene expression?

Related terms

Topoisomerase:

Enzymes that regulate the overwinding or underwinding of DNA.

Nucleoid:

The irregularly-shaped section within prokaryotic cells where genetic material is located.

Transcription:

The process by which a segment of DNA is copied into RNA by RNA polymerase.