TLS Online TPP Program

#Id: 3243

#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.

TLS Online TPP Program

#Id: 3244

#Unit 3. Fundamental Processes

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.

TLS Online TPP Program

#Id: 3245

#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

TLS Online TPP Program

#Id: 3246

#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.

TLS Online TPP Program

#Id: 3247

#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. 

TLS Online TPP Program

#Id: 3248

#Unit 3. Fundamental Processes

One of the most mutagenic base analogs is 5-bromouracil, an analog of thymine.