Answer:
- This process is caused by spontaneous hydrolysis of a glycosidic bond: depurination and deamination
- This process is induced by ultraviolet light: pyrimidine dimer formation
- This can happen to guanine but not to cytosine: depurination
- This can happen to thymine but not to adenine: pyrimidine dimer formation
- This can happen to thymine but not to cytosine: none
- Repair involves a DNA glycosylase: deamination
- Repair involves an endonuclease: depurination, deamination and pyrimidine dimer formation
- Repair involves DNA ligase: depurination, deamination and pyrimidine dimer formation
- Repair depends on the existence of separate copies of the genetic information in the two strands of the double helix: depurination, deamination and pyrimidine dimer formation
- Repair depends on cleavage of both strands of the double helix: none
Explanation:
Depurination is the loss of purine bases (either adenine or guanine), while deamination refers to the removal of an amino group. During depurination, a β-N-glycosidic bond is cleaved by hydrolysis and a nucleic base is released (either adenine or guanine). All DNA bases may undergo deamination, except thymine (since thymine does not have an amino group). The ultraviolet (UV) radiation can cause thymine or cytosine to form dimers (e.g., pyrimidine dimers), being thymine dimers the most common lesion when DNA is exposed to UV light. Pyrimidine dimers may be repaired by different excision mechanisms, e.g., nucleotide excision repair, where the recognition of the DNA damage leads to the removal of the DNA fragment containing the lesion. DNA glycosylases are enzymes involved in the mechanism of base excision, these enzymes recognize and remove damaged bases by hydrolysis of the glycosidic bond, producing an abasic (apurinic and apyrimidinic) site. A DNA ligase enzyme covalently joins two DNA molecules by forming a phosphodiester bond, which is required during these processes.
