Double helix

Definition

A double helix is the structural configuration of DNA, consisting of two intertwined strands that coil around each other, resembling a twisted ladder. This unique shape is crucial for DNA's ability to store genetic information and replicate itself accurately, as the complementary base pairing allows for precise copying during cell division.

5 Must Know Facts For Your Next Test

1. The double helix structure was first described by James Watson and Francis Crick in 1953, based on X-ray diffraction data produced by Rosalind Franklin.
2. The two strands of the double helix are held together by hydrogen bonds between the nitrogenous bases, which allows for easy separation during replication.
3. Each complete turn of the double helix spans about 10 base pairs and has a diameter of approximately 2 nanometers.
4. The arrangement of the sugar-phosphate backbone on the outside and the nitrogenous bases on the inside provides protection to the genetic information stored within.
5. The double helix is not static; it can undergo supercoiling or unwinding depending on cellular processes such as replication and transcription.

Review Questions

• How does the structure of the double helix contribute to its function in genetic information storage?
  • The double helix structure supports genetic information storage by allowing specific base pairing between adenine-thymine and guanine-cytosine, ensuring that sequences can be precisely replicated. This arrangement not only protects the genetic material but also facilitates easy access to these sequences for transcription and replication. The coiled nature of the double helix also optimally packages long strands of DNA within a confined space in cells.
• What role does base pairing play in maintaining the stability of the double helix structure?
  • Base pairing is critical for maintaining the stability of the double helix because it ensures that only complementary bases pair together through hydrogen bonds. This specific pairing creates a consistent width throughout the helix and provides structural integrity. Additionally, it allows for accurate copying of genetic information during DNA replication, as each strand serves as a template for synthesizing a new complementary strand.
• Evaluate the implications of alterations in the double helix structure on genetic function and cell processes.
  • Alterations in the double helix structure can have significant implications for genetic function and cellular processes. For instance, mutations that change the sequence or structure can lead to malfunctioning proteins or diseases like cancer. Furthermore, changes in supercoiling or unwinding can affect replication and transcription efficiency, leading to incomplete or erroneous gene expression. Understanding these alterations helps in identifying genetic disorders and developing therapeutic strategies.

Related terms

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

Base Pairing: The specific hydrogen bonding between complementary nitrogenous bases (adenine with thymine and guanine with cytosine) that stabilizes the double helix structure.

Antiparallel Strands: The orientation of the two strands of the DNA double helix running in opposite directions, which is essential for replication and transcription.