The principal ECM adhesion receptor in epithelial hemidesmosomes is integrin α6β4.

TLS Online TPP Program

#Id: 3238

#Unit 3. Fundamental Processes

transversions, which are pyrimidine-to-purine and purine-to-pyrimidine substitutions, such as T to G or A and A to C or T.

TLS Online TPP Program

#Id: 3240

#Unit 3. Fundamental Processes

Mutations that alter a single nucleotide are called point mutations.

TLS Online TPP Program

#Id: 3241

#Unit 3. Fundamental Processes

Chemical mutagens can be divided into two groups:

those that are mutagenic to both replicating and nonreplicating DNA, such as the alkylating agents and nitrous acid; and 

those that are mutagenic only to replicating DNA, such as base analogs— purines and pyrimidines with structures similar to the normal bases in DNA.

TLS Online TPP Program

#Id: 3242

#Unit 3. Fundamental Processes

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

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.