Answer:
Mutation is basically a process in which a damage or change occurs in the nucleotide sequence of DNA by some mistake.
Mutations can be lethal, cancer causing or even harmless depending on the area of DNA they have damaged.
The cancer causing mutations are those which do not let the cell to divide in a controllable fashion.
Mechanism of cancer causing mutation:
- Basically what happens during cancerous mutations in somatic cells, there are some genes which have the responsibility of proof reading the cell-division process or cell cycle.
- These genes are called proto-oncogenes but when a mutation occurs in these genes they are unable to regulate the cell cycle properly.
- Due to these mutations, the proto-oncogenes are changed into oncogenes or cancenrous genes and lead to the development of cancers.
- What happens after that, the cells divide in an uncontrollable fashion.The effect spreads and soon there is mass of rapidly growing and dividing cells called a tumor, or cancer, However, since they are somatic mutations, they are not transferred to next offspring.
Causes of Somatic mutations:
- Studies suggest that there can be several causes of mutations like smoking, ionizing radiations, physical or chemical mutagens etc. But here our focus will be UV rays as agents of mutations and cancers. Sitting for long hours under sunlight without using a sunscreen can enhance the risk of cancer. Let us see how:
- The UV rays have been associated to sometimes cause two adjacent pyrimidines (thymines, TT, or cytosines, CC) between bases of DNA in such a way that they become linked covalently. These bases form cyclic rings and create an intermediate that is normally nor present in our DNA.
- This type of mutation causes a gap in DNA and prevents normal and perfect replication of DNA and cell which can lead to even cancer. You can see attached figure for better understanding of the formation of thymine dimers.
Hope it help!