Double helix

Definition

The double helix is the structure of DNA, consisting of two long strands that coil around each other, resembling a twisted ladder. This unique shape is essential for DNA's function in storing and transmitting genetic information, as it allows for the complementary base pairing that underlies the mechanisms of replication and transcription.

5 Must Know Facts For Your Next Test

1. The double helix model was first proposed by James Watson and Francis Crick in 1953, based on X-ray diffraction data provided by Rosalind Franklin.
2. Each turn of the double helix contains about 10 base pairs, and the helical structure is stabilized by hydrogen bonds between base pairs and hydrophobic interactions among bases.
3. The specific pairing of adenine with thymine and guanine with cytosine ensures accurate replication during cell division, minimizing mutations.
4. The double helix structure is crucial for DNA's ability to unwind and separate during replication and transcription processes.
5. In addition to its role in encoding genetic information, the double helix allows for the packaging of DNA into chromosomes, facilitating gene regulation and expression.

Review Questions

• How does the structure of the double helix facilitate DNA replication?
  • The double helix's structure allows it to unzip or unwind easily at specific regions during replication. The two strands separate, exposing the bases that serve as templates for new complementary strands. As each strand serves as a template, nucleotides pair according to the base pairing rules, ensuring accurate duplication of genetic information. This process is crucial for cellular division, allowing genetic continuity across generations.
• Discuss how the concept of complementary base pairing contributes to the stability of the double helix structure.
  • Complementary base pairing enhances the stability of the double helix by ensuring that adenine pairs specifically with thymine and guanine pairs with cytosine through hydrogen bonds. This specificity allows for a consistent width along the entire length of the helix. The repeated pairing not only strengthens the overall structure but also provides a mechanism for error-checking during DNA replication, reducing the likelihood of mutations.
• Evaluate the implications of mutations in the double helix structure on genetic diversity and evolution.
  • Mutations in the double helix can lead to changes in genetic sequences, which may introduce new traits within a population. While some mutations can be harmful or lead to diseases, others may confer advantages that enhance survival or reproduction. Over time, these mutations contribute to genetic diversity, providing raw material for natural selection. Thus, understanding how alterations in the double helix affect genetic information is critical for studying evolutionary processes and species adaptation.

Related terms

Nucleotide: The basic building block of DNA, composed of a sugar, a phosphate group, and a nitrogenous base.

Base Pairing: The specific hydrogen bonding between nitrogenous bases in DNA, where adenine pairs with thymine and guanine pairs with cytosine.

Antiparallel Strands: The orientation of the two strands in a double helix where one strand runs in the 5' to 3' direction and the other runs in the opposite 3' to 5' direction.