upgrade

🔬general biology i review

Five-carbon sugar

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

Definition

A five-carbon sugar, also known as pentose, is a type of carbohydrate that contains five carbon atoms in its molecular structure. These sugars play a crucial role in the formation of nucleotides, which are the building blocks of nucleic acids like DNA and RNA. The two main types of five-carbon sugars are ribose and deoxyribose, each differing slightly in their structure and function within nucleic acids.

5 Must Know Facts For Your Next Test

  1. Five-carbon sugars can exist in linear and cyclic forms, with the cyclic form being more common in biological systems.
  2. Ribose is used to make RNA, while deoxyribose is found in DNA; this small difference is crucial for the distinct roles these nucleic acids play in cells.
  3. In addition to their roles in nucleic acids, five-carbon sugars can be involved in various metabolic pathways and are important for energy production.
  4. The presence of hydroxyl (–OH) groups on ribose makes it more reactive compared to deoxyribose, influencing the stability and function of RNA.
  5. Five-carbon sugars are synthesized from glucose through various metabolic pathways, showing the interconnectedness of carbohydrate metabolism.

Review Questions

  • How do the structures of ribose and deoxyribose differ, and why is this difference significant for their functions in nucleic acids?
    • Ribose and deoxyribose differ by one oxygen atom; ribose has an –OH group on the second carbon, while deoxyribose has only a hydrogen atom at that position. This difference is significant because it impacts the stability and reactivity of RNA compared to DNA. The presence of the hydroxyl group in ribose makes RNA more reactive and less stable than DNA, which is more suited for long-term information storage.
  • Discuss how five-carbon sugars contribute to the structure and function of nucleotides in DNA and RNA.
    • Five-carbon sugars are integral components of nucleotides, which consist of a nitrogenous base, a phosphate group, and a five-carbon sugar. In DNA, deoxyribose connects to adenine, thymine, cytosine, or guanine to form the nucleotide structure necessary for genetic information storage. In RNA, ribose connects to adenine, uracil, cytosine, or guanine, enabling protein synthesis and other cellular functions. The structural differences between these sugars directly influence the roles that DNA and RNA play within cells.
  • Evaluate the role of five-carbon sugars in cellular metabolism and how they connect with larger metabolic pathways.
    • Five-carbon sugars are not only essential for nucleic acid structure but also play a key role in cellular metabolism. They can be produced from glucose through pathways like the pentose phosphate pathway, which generates ribose-5-phosphate necessary for nucleotide synthesis. Furthermore, five-carbon sugars can participate in the synthesis of various biomolecules and energy metabolism. Their ability to connect with larger metabolic pathways underscores their importance beyond just being structural components of nucleotides.