Double helix

Definition

The double helix is the twisted ladder-like structure of DNA, formed by two long strands of nucleotides running in opposite directions, coiled around each other. This unique shape allows for the compact storage of genetic information while providing stability and the ability for the molecule to replicate accurately during cell division. The arrangement of complementary base pairs within the double helix is crucial for processes such as DNA replication and transcription.

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 from Rosalind Franklin.
2. Each complete turn of the double helix consists of about 10 base pairs, providing structural stability.
3. The sugar-phosphate backbone of each strand forms the outer part of the helix, while the nitrogenous bases face inward, forming the rungs of the ladder.
4. The double helix is stabilized by hydrogen bonds between complementary base pairs and hydrophobic interactions between the bases.
5. The replication of DNA occurs when the double helix unwinds, allowing each strand to serve as a template for synthesizing new complementary strands.

Review Questions

• How does the structure of the double helix contribute to its function in storing genetic information?
  • The double helix structure efficiently organizes and compacts genetic information within a small space. The specific pairing of nitrogenous bases ensures that the genetic code is preserved during replication, as each strand serves as a template for creating a new complementary strand. This design not only protects the information but also facilitates accurate copying during cell division.
• Discuss how the antiparallel nature of DNA strands impacts DNA replication.
  • The antiparallel orientation of DNA strands means that they run in opposite directions, which is essential for replication. DNA polymerases can only synthesize new DNA in a 5' to 3' direction. As a result, one strand, known as the leading strand, is synthesized continuously, while the other strand, called the lagging strand, is synthesized in short fragments called Okazaki fragments. This organization ensures that both strands are replicated accurately despite their opposing orientations.
• Evaluate the importance of base pairing within the double helix in relation to mutations and genetic variability.
  • Base pairing is fundamental for maintaining genetic fidelity during DNA replication. However, errors can occur during this process, leading to mutations. These mutations can alter base pair sequences, which may introduce genetic variability within populations. While many mutations are neutral or harmful, some can provide advantageous traits that contribute to evolution. Thus, base pairing not only ensures accurate information storage but also plays a key role in genetic diversity and adaptation.

Related terms

Nucleotide: The building blocks of DNA and RNA, 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 cytosine pairs with guanine.

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