Double helix

Definition

The double helix is a molecular structure of DNA consisting of two long strands that coil around each other, resembling a twisted ladder. This unique shape is essential for the stability of the DNA molecule and plays a critical role in genetic replication and expression. The two strands are held together by base pairs formed between nucleotides, which provide the genetic instructions necessary for all living organisms.

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 data from Rosalind Franklin's X-ray diffraction images.
2. The two strands of the double helix run in opposite directions, referred to as antiparallel orientation, which is crucial for replication and enzyme binding.
3. Each complete turn of the double helix spans approximately 10 base pairs, giving it a consistent width and allowing for efficient packing within the cell nucleus.
4. The hydrogen bonds between base pairs are relatively weak, allowing the strands to separate easily during DNA replication and transcription.
5. Mutations in the DNA sequence can disrupt the double helix structure, leading to potential consequences for cellular function and organism development.

Review Questions

• How does the structure of the double helix facilitate DNA replication?
  • The structure of the double helix allows for easy separation of the two strands during DNA replication. The weak hydrogen bonds between the base pairs enable the strands to unwind without breaking, providing access to the nucleotide sequences. This unwinding allows enzymes like DNA polymerase to synthesize new complementary strands by matching nucleotides with the original template strands.
• In what ways do base pairing rules support the stability and function of the double helix structure?
  • Base pairing rules ensure that adenine always pairs with thymine and guanine always pairs with cytosine, forming stable hydrogen bonds that hold the two strands together. This specificity not only contributes to the stability of the double helix but also plays a vital role in accurate DNA replication and transcription processes. Errors in base pairing can lead to mutations, impacting genetic information transmission.
• Evaluate the implications of double helix structural changes on gene expression and cellular processes.
  • Changes in the double helix structure, such as those caused by mutations or chemical modifications, can have profound effects on gene expression. If the double helix is distorted or damaged, it may hinder the ability of transcription factors and RNA polymerase to bind effectively, reducing or completely stopping gene expression. Such alterations can disrupt normal cellular processes and lead to diseases like cancer, highlighting the importance of maintaining structural integrity for proper cellular function.

Related terms

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

Base Pairing: The specific pairing of nitrogenous bases in DNA, where adenine pairs with thymine and guanine pairs with cytosine.

DNA Replication: The biological process of copying a double-stranded DNA molecule to produce two identical DNA molecules.