Topoisomer

Illustration of different DNA topoisomers.

A topoisomer is one of a set of molecules that have the same chemical formula and stereochemistry but differ in the topology of their molecular structure. Topoisomers are particularly important in the study of DNA, where they refer to different forms of DNA that differ in their supercoiling or linking number.

DNA Topoisomers

In the context of DNA, topoisomers are DNA molecules that have the same sequence but differ in their topological properties. DNA can exist in various topological forms, such as relaxed, supercoiled, or knotted. These forms are interconvertible through the action of topoisomerase enzymes, which can cut and rejoin the DNA strands to change the linking number.

Supercoiling

Supercoiling refers to the over- or under-winding of a DNA strand, and is an important aspect of DNA topology. Supercoiling is a natural state of DNA in cells and is crucial for DNA compaction and regulation of gene expression. DNA topoisomers with different degrees of supercoiling can be separated by gel electrophoresis, as they migrate differently due to their distinct shapes and sizes.

Topoisomerases

Topoisomerases are enzymes that play a critical role in managing DNA topology. They can introduce or remove supercoils by transiently breaking one or both strands of the DNA, allowing the DNA to be untwisted or untangled, and then resealing the breaks. There are two main types of topoisomerases: Type I, which cut one strand of DNA, and Type II, which cut both strands.

Applications and Importance

Understanding DNA topoisomers is essential in molecular biology and genetics. The study of DNA topology is important for understanding processes such as DNA replication, transcription, and chromosome segregation. Topoisomerases are also targets for certain antibiotics and anticancer drugs, making them significant in medicine.

Related pages

• DNA topology
• Topoisomerase
• Supercoiling
• Molecular biology

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