Lys & Arg have four ionisations zones

1. 1--------pK1 – charge +2

2. pK1---------pK2 charge +1

3. pK2---------pKr charge 0

4. pKr---------14 charge -1

TLS Online TPP Program

#Id: 3333

#Unit 3. Fundamental Processes

Humans can exhibit a genetic disorder called xeroderma pigmentosum (XP), an autosomal-recessive disease that renders afflicted individuals highly sensitive to sunlight and results in skin lesions, including skin cancer.

TLS Online TPP Program

#Id: 3335

#Unit 3. Fundamental Processes

Seven genes have been identified in which mutations give rise to XP, these genes specify proteins (such as XPA, XPC, XPD, XPF, and XPG;)

TLS Online TPP Program

#Id: 3337

#Unit 3. Fundamental Processes

In addition to proteins involved in NER, a variant form of XP called XP-V is caused by a defect in the translesion DNA polymerase, Pol h. The gene encoding Pol h is sometimes called XPV. Individuals with XP-V have a milder form of XP.

TLS Online TPP Program

#Id: 3339

#Unit 3. Fundamental Processes

Cells possessing a mutant Pol h are hindered in their ability to bypass thymine dimers during replication and must resort to using another translesion polymerase for bypass to avoid a block in replication. 

TLS Online TPP Program

#Id: 3346

#Unit 3. Fundamental Processes

Pol h (but not other translesion polymerases) correctly inserts As across from a thymine dimer, the use of other translesion polymerases may increase the frequency of mutagenesis

TLS Online TPP Program

#Id: 3348

#Unit 3. Fundamental Processes

Direct repair of alkylated bases by AlkB