Double helix

Definition

The double helix is the molecular structure of DNA, consisting of two long strands that spiral around each other, resembling a twisted ladder. This unique shape is crucial for the stability and function of DNA, allowing it to store genetic information and facilitate processes such as replication and transcription.

5 Must Know Facts For Your Next Test

1. The double helix was first described by James Watson and Francis Crick in 1953, based on X-ray diffraction data from Rosalind Franklin.
2. The two strands of the double helix are held together by hydrogen bonds between the nitrogenous bases, which provide stability to the structure.
3. The antiparallel nature of the strands is essential for DNA replication and transcription, allowing enzymes to read the genetic code correctly.
4. The major and minor grooves formed by the twisting of the double helix are important sites for protein binding, playing a role in gene regulation.
5. Mutations in the DNA structure can occur if there are errors during replication or environmental damage, affecting genetic stability.

Review Questions

• How does the structure of the double helix contribute to its function in storing genetic information?
  • The double helix's structure allows for efficient storage of genetic information due to its compact form. The sequence of nitrogenous bases along the strands encodes genetic instructions, while the complementary base pairing ensures that this information can be accurately replicated during cell division. Additionally, the helical shape protects the genetic material from damage and allows for accessibility by enzymes that need to read or copy the DNA.
• What role does base pairing play in maintaining the integrity of the double helix during DNA replication?
  • Base pairing is fundamental to maintaining the integrity of the double helix during DNA replication. As DNA unwinds, each strand serves as a template for synthesizing a new complementary strand. The specific pairing—adenine with thymine and guanine with cytosine—ensures that the correct bases are added, preserving the original sequence. This accuracy is vital for passing on genetic information to daughter cells.
• Evaluate how structural features of the double helix influence interactions with proteins involved in gene regulation.
  • Structural features of the double helix, such as the major and minor grooves, create specific binding sites for regulatory proteins. These grooves provide access to the nitrogenous bases without needing to unwind the entire DNA molecule. Proteins that bind to these sites can either promote or inhibit gene expression by influencing transcription factors' access to necessary regions of DNA. Thus, the shape and configuration of the double helix are essential for regulating gene activity in response to cellular signals.

Related terms

Nucleotide: The basic building block of DNA and RNA, consisting 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, ensuring accurate replication and information transfer.

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