upgrade

🔬general biology i review

Purine-pyrimidine pairing

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Purine-pyrimidine pairing refers to the specific hydrogen bonding interactions between purine and pyrimidine bases in nucleic acids, particularly DNA. In DNA, adenine (A) and guanine (G) are purines, while cytosine (C) and thymine (T) are pyrimidines. This pairing is essential for the stability of the DNA double helix structure, as it allows for complementary base pairing that ensures accurate replication and transmission of genetic information.

5 Must Know Facts For Your Next Test

  1. Purines form two hydrogen bonds with pyrimidines in DNA: adenine pairs with thymine, and guanine pairs with cytosine.
  2. The specific pairing of purines and pyrimidines maintains the uniform width of the DNA double helix, which is crucial for its stability.
  3. During DNA replication, purine-pyrimidine pairing ensures that genetic information is accurately copied and passed on to daughter cells.
  4. Errors in purine-pyrimidine pairing can lead to mutations, which may have significant consequences for an organism's traits and health.
  5. The energy required for the formation of these hydrogen bonds contributes to the overall stability of the DNA molecule.

Review Questions

  • How does purine-pyrimidine pairing contribute to the stability of the DNA double helix?
    • Purine-pyrimidine pairing enhances the stability of the DNA double helix through specific hydrogen bonding interactions that occur between complementary bases. Adenine pairs with thymine through two hydrogen bonds, while guanine pairs with cytosine through three hydrogen bonds. This consistent pairing keeps the two strands aligned at a uniform width, providing structural integrity and resilience against environmental factors that could damage the DNA.
  • Discuss the implications of incorrect purine-pyrimidine pairing during DNA replication.
    • Incorrect purine-pyrimidine pairing during DNA replication can result in mutations that alter the genetic sequence. For example, if adenine pairs with cytosine instead of thymine, this mispairing can lead to errors in the genetic code. Such mutations may have varying consequences, ranging from neutral effects to significant changes in phenotype or disease susceptibility. The cell's repair mechanisms must address these mismatches to maintain genomic integrity.
  • Evaluate how purine-pyrimidine pairing is integral to understanding genetic inheritance and variation.
    • Purine-pyrimidine pairing is fundamental to genetic inheritance because it ensures accurate replication and transmission of genetic information from one generation to the next. The fidelity of this pairing influences how traits are inherited and how variations arise through mutations. Understanding this mechanism allows researchers to explore genetic diversity within populations and how certain alleles can confer advantages or disadvantages based on their base sequences, ultimately impacting evolution and natural selection.