UV irradiation causes damage to bacterial DNA. What kind of damage is frequently caused and how does photolyase repair the damage?

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1. span>UV irradiation frequently causes the formation of pyrimidine dimers, particularly thymine dimers, in bacterial DNA. These dimers result from covalent bonding between adjacent thymine bases on the same DNA strand, disrupting normal base pairing and DNA replication.
2. span>Photolyase is an enzyme that specifically recognizes and binds to these pyrimidine dimers in the DNA.
3. span>Once bound, photolyase absorbs light, typically in the blue or near-UV spectrum, which provides the energy needed for the repair process.
4. span>The absorbed light energy is used by photolyase to break the covalent bonds between the thymine bases, effectively reversing the dimerization and restoring the normal base pairing.
5. span>This repair mechanism is known as photoreactivation, and it is a direct reversal of the DNA damage caused by UV irradiation.

Key Concepts

UV-Induced DNA Damage

Ultraviolet (UV) irradiation can cause various types of damage to DNA, with the most common being the formation of pyrimidine dimers, particularly thymine dimers. These dimers occur when adjacent thymine bases bond together, disrupting the normal base pairing and leading to replication errors if not repaired.

Photolyase Enzyme

Photolyase is a light-dependent enzyme that repairs UV-induced DNA damage, specifically pyrimidine dimers. It utilizes energy from visible light to cleave the bonds between the dimerized bases, restoring the DNA to its original state and allowing normal replication and transcription to occur.

DNA Repair Mechanisms

DNA repair mechanisms are essential cellular processes that correct damage to DNA. In addition to photolyase, other repair systems like nucleotide excision repair (NER) and base excision repair (BER) exist, which recognize and remove damaged sections of DNA, followed by synthesis of new DNA to fill the gaps.