Infectious diseases are disorders caused by organisms — such as bacteria, viruses, fungi or parasites

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#Unit 3. Fundamental Processes

The most frequent and important kind of hydrolytic damage is deamination of the base cytosine.

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#Unit 3. Fundamental Processes

Adenine and guanine are also subject to spontaneous deamination. Deamination converts adenine to hypoxanthine, which hydrogen-bonds to cytosine rather than to thymine; guanine is converted to xanthine,

which continues to pair with cytosine, although with only two hydrogen bonds.

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DNA also undergoes depurination by spontaneous hydrolysis of the N-glycosyl linkage, and this produces an abasic site (i.e., deoxyribose lacking a base) in the DNA.

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#Unit 3. Fundamental Processes

Common types of hydrolytic DNA damage.

Deamination of cytosine creates uracil

Depurination of guanine by hydrolysis creates apurinic deoxyribose

Deamination of 5-methylcytosine generates a natural base in DNA, thymine

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#Unit 3. Fundamental Processes

G modification. The figure shows specific sites on guanine that are vulnerable to damage by chemical treatment, such as alkylation or oxidation, and by radiation.

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#Unit 3. Fundamental Processes

Mutations are also caused by compounds that substitute for normal bases (base analogs) or slip between the bases (intercalating agents) to cause errors in replication.