Double helix

Definition

The double helix is the structure formed by double-stranded molecules of nucleic acids such as DNA. It consists of two complementary strands that coil around each other to form a helical shape.

5 Must Know Facts For Your Next Test

1. The double helix structure was discovered by James Watson and Francis Crick in 1953.
2. Each strand of the double helix is composed of nucleotide subunits that include a phosphate group, a deoxyribose sugar, and a nitrogenous base.
3. The two strands are held together by hydrogen bonds between complementary bases: adenine pairs with thymine, and guanine pairs with cytosine.
4. The antiparallel nature of the strands means they run in opposite directions, one from 5' to 3' and the other from 3' to 5'.
5. DNA replication relies on the unwinding of the double helix to allow each strand to serve as a template for creating new complementary strands.

Review Questions

• Who are credited with discovering the double helix structure of DNA?
• What type of bonds hold the two strands of the DNA double helix together?
• Explain what is meant by the antiparallel nature of DNA strands.

Related terms

Nucleotide:

The basic building block of nucleic acids, consisting of a phosphate group, a sugar molecule, and a nitrogenous base.

Complementary Base Pairing:

A principle stating that in DNA, adenine pairs with thymine and guanine pairs with cytosine.

Antiparallel:

Refers to the opposite orientation of the two strands in a DNA molecule.