key term - Cytosine Dimers

Definition

Cytosine dimers are a type of DNA damage that occurs when two adjacent cytosine bases in a DNA strand become covalently linked due to exposure to ultraviolet (UV) light. This abnormal bonding distorts the DNA structure, leading to replication errors and potentially harmful mutations if not repaired. The formation of cytosine dimers is a significant concern for cellular integrity and is a focus of various DNA repair mechanisms.

5 Must Know Facts For Your Next Test

1. Cytosine dimers primarily form due to exposure to UV radiation, which can occur from sunlight or artificial sources like tanning beds.
2. If not repaired, cytosine dimers can lead to mutations during DNA replication, contributing to issues like skin cancer and other genetic disorders.
3. The human body has evolved several repair mechanisms specifically targeting cytosine dimers, highlighting their potential threat to genomic stability.
4. Cytosine dimers are often detected using specialized techniques in molecular biology, allowing researchers to study the extent of UV damage in cells.
5. The presence of cytosine dimers can serve as a marker for environmental exposure to UV light, making them relevant in studies of skin health and cancer risk.

Review Questions

• What causes the formation of cytosine dimers and how do they affect the structure of DNA?
  • Cytosine dimers are formed primarily due to exposure to ultraviolet (UV) light, which causes two adjacent cytosine bases in the DNA strand to bond covalently. This abnormal linkage distorts the double helix structure of DNA, potentially leading to mispairing during replication. If left unrepaired, these distortions can result in mutations and contribute to various genetic disorders.
• Discuss the role of nucleotide excision repair in fixing cytosine dimers and the implications if this repair mechanism fails.
  • Nucleotide excision repair plays a crucial role in repairing cytosine dimers by detecting and removing the damaged segment of DNA. The process involves cutting out the dimerized nucleotides and synthesizing new nucleotides to fill the gap. If this repair mechanism fails, it can lead to persistent mutations that disrupt normal cellular function and increase the risk of diseases such as cancer.
• Evaluate the significance of photoreactivation as a mechanism for repairing cytosine dimers in comparison to other repair methods.
  • Photoreactivation is significant because it directly reverses the formation of pyrimidine dimers like cytosine dimers using visible light. This method is efficient and restores the original DNA structure without removing any nucleotides. In comparison to nucleotide excision repair, which involves a more complex process of cutting out damaged sections and resynthesizing DNA, photoreactivation provides a quicker solution for cells exposed to UV light. Understanding these mechanisms highlights how organisms have adapted to environmental stressors that can cause DNA damage.

Related terms

Thymine Dimers: Thymine dimers are similar to cytosine dimers, where two adjacent thymine bases bond together, causing distortions in the DNA that can lead to replication errors.

Nucleotide Excision Repair: A DNA repair mechanism that removes damaged nucleotides, including cytosine dimers, by cutting out a segment of the DNA strand and filling it in with correct nucleotides.

Photoreactivation: A repair process that uses light energy to directly reverse the formation of pyrimidine dimers, including cytosine dimers, restoring the DNA to its original state.