Key Questions

  • Answer:

    XP skin tumors have detected several (N-ras, c-myc, Ha-ras) altered oncogenes. These modifications primarily due to the presence of unrepaired UV Radiation adducts(these adducts are pyrimidine dimers, in which two adjacent pyrimidines mostly thymine are joined by a cyclobutane ring).


    UV Radiation damages cause large distortion in DNA helical structure.This kind of DNA distortion is repaired by nucleotide excision repair system,which is very crucial for the all living organisms.If this damage does not repair, it will cause severe dieases such as xeroderma pigmentosum and Cockayne syndrome.Affected Individuals have extreme sensitivity to the sunlight and develop skin cancers due to the thymine dimer passing on generation to generation.The DNA damage cause by the UV rays is remarkably linked at the transcriptional level(when mRNA is formed from the template DNA) .In the normal individuals,during transcription RNA Polymersase becomes stalled at a region of damaged template DNA, The transcription factor II H recognises the stalled RNA polymerase and repair the damage region of the DNA with the aid of other proteins.Individuals with the mutant form of the transcription factor II H cause unrepaired damage of the DNA and develop severe skin cancers mentioned as xeroderma pigmentosum.

  • Mitosis is the process of cells growing and dividing, hence replicating themselves. Cancer is simply uncontrolled cell division.

    In the cell, mitosis is always tightly regulated. If the cell has errors in it (faulty DNA, for example), the regulator proteins will not allow it to divide.

    In addition, there are several processes that stimulate cell growth. For example, if cells receive certain signals, then they begin to divide.

    Now if either of these two processes was faulty, it would lead to uncontrolled mitosis, and cancer. For example, if the stimulant kept stimulating even when it isn't supposed to, or the regulator proteins do not regulate properly, then the cell can become cancerous.