Double helix

Double Helix

The double helix is the description of the structure of a deoxyribonucleic acid (DNA) molecule. DNA is the molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses.

Discovery

The double helix structure of DNA was first discovered by James Watson and Francis Crick in 1953, with significant contributions from Rosalind Franklin and Maurice Wilkins. Their discovery was based on X-ray crystallography data, which provided critical insights into the three-dimensional structure of DNA.

Structure

The DNA double helix consists of two long strands of nucleotides twisted around each other. Each nucleotide is composed of a sugar molecule, a phosphate group, and a nitrogenous base. The backbone of each strand is formed by the sugar and phosphate groups, while the nitrogenous bases extend inward.

Base Pairing

The nitrogenous bases pair specifically: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). These pairs are held together by hydrogen bonds, with A-T pairs forming two hydrogen bonds and C-G pairs forming three hydrogen bonds. This specific pairing is known as complementary base pairing.

Antiparallel Strands

The two strands of the double helix run in opposite directions, a feature known as antiparallel orientation. One strand runs in a 5' to 3' direction, while the other runs 3' to 5'. This orientation is crucial for the replication and transcription processes.

Function

The double helix structure of DNA allows it to perform its essential functions:

• Replication: The double helix can be "unzipped" to allow each strand to serve as a template for the creation of a new complementary strand. This is the basis for DNA replication.
• Encoding Information: The sequence of bases along a DNA strand encodes genetic information, which is used to synthesize proteins through the processes of transcription and translation.

Significance

The discovery of the double helix was a pivotal moment in the field of molecular biology. It provided a clear mechanism for genetic inheritance and laid the foundation for modern genetics. The understanding of DNA's structure has led to numerous advances in biotechnology, medicine, and forensic science.

Further Reading

• Molecular Biology of the Cell
• The Double Helix: A Personal Account of the Discovery of the Structure of DNA by James D. Watson

References

• Watson, J. D., & Crick, F. H. C. (1953). "Molecular structure of nucleic acids: A structure for deoxyribose nucleic acid." Nature, 171(4356), 737-738.
• Franklin, R. E., & Gosling, R. G. (1953). "Molecular configuration in sodium thymonucleate." Nature, 171(4356), 740-741.