Question

Chemicals or radiation may alter a nucleotide base in one strand of DNA; this alteration may cause the altered base to pair with a nucleotide base other than its normal one. What effect would this accidental change in the base sequences of the DNA molecule have on DNA replication?

Answer 1

- Environmental exposures to radiations or certain chemicals leads to change in DNA and also damaged that DNA.

- These external agents which are responsible for the change are called mutagen and the process is called as mutation.

- These mutaions occur during DNA replication.

- Mutations are of various types and are harmful to the organisms.

- Ionising radiations causes two types of injuries- somatic injury and genetic injury.

- Many chemials such as cadmium, lead , mercury also cause the damage to the DNA molecule..

Types of mutation-

1) Base substitution-

- In this process Thymine nucleotide might be inserted in the place of Guanine nucleotide. As only single nucleotide is changed hence only one codon is affected.

2) Missense mutation-

- In this process insertion of incorrect amino acid in the protein molecule take place.

3) Non sense mutation-

- In this process an altered codon terminates the process of protein synthesis.

4) Silent mutation-

- In this codon gets altered but it codes for same amino acid.

5) Insertion mutation -

- During replication an extra nucleotide is addes to the strand.

6) Deletion mutation-

- Here one of the nucleotide is deleted from the DNA strand.